The objection Darwin knew would be hardest to answer was not about bones or fossils. It was about conscience. As long as the moral sense could be held apart from animal life, the distance between human beings and other creatures remained intact. Rev. Leonard Jenyns made exactly this argument in a letter to Darwin in January 1860, writing that he could not bring himself to accept that “man’s reasoning faculties and above all his moral sense could ever have been obtained from irrational progenitors, by mere natural selection.” Take the moral sense out of nature and you preserve, as Jenyns put it, “the Divine Image that forms the insurmountable distinction between man and brutes.”

Darwin’s response, worked out across Chapters 3 and 5 of The Descent of Man (1871), was not to deny that the moral sense was special. It was to explain where it came from without appealing to anything outside the natural world. The argument is more specific, and stranger, than it is usually remembered.

The hypothesis Darwin actually made

Darwin’s central claim was a conjecture he stated plainly near the opening of Chapter 4: “any animal whatever, endowed with well-marked social instincts, the parental and filial affections being here included, would inevitably acquire a moral sense or conscience, as soon as its intellectual powers had become as well, or nearly as well developed, as in man.”

This is worth reading carefully. Darwin was not saying that morality evolved because it was useful to individuals. He was not saying that conscience is simply clever self-interest. He was saying that if you take social instincts, which already exist in many species, and combine them with sufficient intelligence, memory, and language, something like a conscience is the outcome. Not a chosen outcome. An inevitable one.

The social instincts Darwin had in mind were real biological tendencies: propensities to take pleasure in the company of others, to feel something like sympathy with them, and to perform services for them. These tendencies, he argued, are persistent. They do not disappear when they are overridden. Other impulses, hunger, desire, self-preservation, can suppress social instincts in a given moment, but the social instincts persist as a background disposition, always present, always able to reassert themselves once the pressing impulse has passed.

Where memory enters the argument

The mechanism Darwin proposed for the emergence of conscience depends on memory. An animal with strong social instincts but no memory of its past actions cannot experience the conflict between what it did and what its social nature would have preferred. It acts, it satisfies an appetite, and it moves on. The social instinct, frustrated but not forgotten, leaves no trace.

Add memory, and the calculation changes entirely. After an act that violated social instinct, that persistent social feeling reasserts itself in memory and produces a disagreeable feeling that Darwin described with precision: “He will then feel remorse, repentance, regret, or shame.” This is conscience, in his account. Not a divine faculty. Not a special human endowment. It is the collision, remembered, between what was done and what the social nature would have preferred. “Conscience looks backwards,” he wrote, “and serves as a guide for the future.”

Memory alone is not enough. Darwin added language as the mechanism by which communities build explicit shared norms, what he called “public opinion” as to how members should act for the common benefit. These norms are conventional, not instinctive. Their content varies across cultures and times. But their binding force, Darwin argued, depends on something that is instinctive: sympathy. “Our regard for the approbation and disapprobation of our fellows depends on sympathy, which forms an essential part of the social instinct, and is indeed its foundation-stone.”

The consequence of how we understand civilisation

If this argument is substantially right, a particular way of thinking about manners, conscience, and moral restraint becomes harder to hold. The traditional view treats these things as the victory of something higher over something lower: reason over appetite, culture over nature, the civilised over the animal. Darwin’s account does not work that way. Manners are not the suppression of instinct. They are one set of instincts, the social ones, as they have been elaborated and made explicit through memory, language, and the accumulated judgments of people living together.

Restraint is not the opposite of instinct. It is what instinct looks like after it has been complicated by the awareness that others are watching and will remember.

This is unsettling in a specific way. It means that the moral progress of a society cannot be understood as a movement away from biology toward something purely rational or conventional. It means that the social instincts, those old biological tendencies toward sympathy and mutual regard, are doing continuous work underneath the surface of any functioning moral culture. When those instincts weaken, when the conditions that maintain sympathy erode, there is no backup system of pure reason to fill the gap.

What Darwin acknowledged the argument could not do

Darwin was a careful enough thinker to register the difficulty his own account ran into. He wanted to say that the social instincts, including sympathy, were themselves products of natural selection. But natural selection works on individuals, and sympathy is a propensity that benefits others, sometimes at the individual’s expense. He gestures toward what would later be called group selection, the idea that tribes with more cooperative members outcompete those without, and toward something close to kin selection. He did not resolve it. The mechanisms that actually account for the evolution of altruistic behaviour were worked out in the twentieth century by W. D. Hamilton and Robert Trivers, building on foundations Darwin laid.

There is a further limitation worth naming. Darwin’s account of conscience as social-instinct-plus-memory is a psychological and evolutionary account. It describes how the moral sense likely arose and what it is composed of. It does not, by itself, tell us what we ought to do. Darwin was explicit about this. He was more cautious than Herbert Spencer and others who tried to derive ethical prescriptions directly from evolutionary facts. What evolution explains is the origin of our moral faculties, including their biases, their reach, their limitations. It is not a replacement for moral reasoning.

The reading that travels farthest

What we keep coming back to in Darwin’s account is how little of it requires the human animal to be exceptional in the ways that traditional moral philosophy assumed. The components he identifies, social instinct, memory, language, the sensitivity to others’ approval and disapproval, are not inventions unique to our species. They are elaborations, remarkable ones, of tendencies that appear in recognisable forms across many social animals.

This does not diminish the moral achievements of human cultures. It relocates them. What seems to belong to a separate, higher domain turns out to be built from materials that were already present, already working, long before anything we would call civilisation. The notebooks Darwin kept in 1838, more than thirty years before The Descent of Man was published, already contain the essential idea, written in his characteristic shorthand: “Society could not go on except for the moral sense, any more as a hive of Bees without their instincts.”

The comparison to bees was not meant as a reduction. It was meant as an observation about what holds any social life together. The moral sense, in Darwin’s reading, is not a ceiling above our animal nature. It is something that grew from within it, shaped by the fact that we live together, remember our actions, care what others think of us, and inherit the social tendencies of creatures far older than ourselves.

The post Charles Darwin argued that the roots of human morality were not separate from animal life, and the surprise is what that does to civilization — manners, conscience, and restraint become not the opposite of instinct, but instinct complicated by memory, language, and the judgment of others appeared first on Space Daily.

The World Health Statistics 2026 report, published by the World Health Organization on 13 May, carries a paradox on almost every page. The gains it documents are genuine. A 40 percent reduction in new HIV infections between 2010 and 2024. A 36 percent drop in the number of people requiring interventions for neglected tropical diseases over the same period. The WHO’s African Region achieved faster reductions in new HIV infections than the global average — down 70 percent since 2010 compared with 40 percent globally — and also outpaced the global rate on tuberculosis. These are not small movements. They represent millions of lives in different conditions than they would otherwise have been.

The report also states that the world is “off track to achieve any of the health-related Sustainable Development Goals by 2030,” that progress in many areas has slowed, and that in some it has reversed. The HIV and NTD figures are cited as among the bright points. But the infrastructure that produced them, the funding systems, the programmes, and the health systems they flow through, is now under significant and specific pressure.

What the HIV figure represents

A 40 percent reduction in new infections across fourteen years is a result of sustained investment in prevention, testing, antiretroviral treatment access, and targeted behavioural programmes. No single intervention produced it. The figure reflects the cumulative effect of programmes that operated at scale, consistently, over a long period.

The United States has historically been the largest single contributor to international HIV funding, providing around 73 percent of all donor funding for HIV programmes in low- and middle-income countries in 2023, primarily through the President’s Emergency Plan for AIDS Relief, known as PEPFAR. Early in 2025, USAID grant holders were instructed to stop work. Testing counsellors and clinic staff were laid off in the same period. Studies from Mozambique and South Africa documented immediate drops in HIV testing and new treatment initiations in the first quarter of 2025. Modelling work published by UNAIDS in 2025 projected that if US-supported programmes were halted without equivalent replacement, there could be more than 6 million additional new HIV infections by 2030 — potentially returning infection levels to those not seen since the early 2000s.

Neglected tropical diseases and what the 36% figure includes

Neglected tropical diseases, or NTDs, are a group of conditions, including lymphatic filariasis, trachoma, schistosomiasis, and several others, that predominantly affect people living in poverty in tropical and subtropical regions. The 36 percent reduction in the number of people requiring interventions between 2010 and 2024 reflects a combination of mass drug administration programmes, improved sanitation, and sustained public health campaigns that, like the HIV work, required consistent funding and logistical infrastructure over many years.

The gains in this area are concentrated in specific regions and specific diseases. They are not uniformly distributed. And because NTD programmes depend on donated medicines, coordinated delivery, and community health infrastructure that is itself dependent on external funding, they are vulnerable to the same financing pressures that now affect HIV programmes.

Where the broader picture is worse

The HIV and NTD improvements are among the few areas where the World Health Statistics 2026 report can present an unambiguously positive trajectory. Much of the rest of the data is more difficult.

Progress toward universal health coverage has slowed sharply. The WHO’s service coverage index rose only from 68 to 71 between 2015 and 2023. One quarter of the global population faced financial hardship from health costs. Around 1.6 billion people were living in or pushed into poverty from out-of-pocket health spending in 2022. Malaria incidence increased by 8.5 percent since 2015. Anaemia affects 30.7 percent of women of reproductive age, with no improvement over the past decade. Childhood vaccination coverage remains below target.

The COVID-19 pandemic’s shadow runs through the report. Between 2020 and 2023, it is linked to an estimated 22.1 million excess deaths, including indirect deaths. That figure is more than three times the number of officially reported COVID-19 deaths. The WHO states that this reversed a decade of gains in life expectancy, and that recovery remains incomplete and uneven.

The data gap underneath all of this

There is a further problem the report names directly. As of the end of 2025, only 18 percent of countries were reporting mortality data to WHO within one year. Nearly one third have never reported cause-of-death data. Of the estimated 61 million deaths globally in 2023, only around one third were reported with cause-of-death information, and roughly one fifth had usable coded data.

This matters for how to read all the figures above, including the gains. The 40 percent reduction in HIV infections and the 36 percent drop in NTD burden are derived from the best available data. Where data collection is poor, those estimates carry more uncertainty. The WHO notes this not to undercut its own figures but because the data gap affects the ability to monitor whether progress is holding, slipping, or reversing in real time. Progress built on incomplete reporting is harder to protect.

What the WHO is asking for

Dr Tedros Adhanom Ghebreyesus, the WHO Director-General, said in the report’s accompanying statement that “investing in stronger, more equitable health systems, including resilient health data systems is essential to target action, close gaps and ensure accountability.” Dr Yukiko Nakatani, the WHO Assistant Director-General for Health Systems, named “a worsening health financing crisis” as one of the conditions requiring urgent response, alongside rising environmental risks and ongoing health emergencies.

The language is institutional and measured. The situation it describes is not. A decade of measurable progress in two of the most intractable areas of global health is now contingent on decisions about funding that are being made in contexts entirely external to the public health systems that produced the gains. The WHO’s report is, among other things, a record of what was built and a description of how fragile the conditions for maintaining it have become.

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The popular framing of emotional pain treats it as something metaphorical. The broken heart of unrequited love, the sting of rejection, the ache of grief, the cutting remark, the wound that will not heal: the language of physical injury used to describe emotional injury is so widespread across cultures and languages that it has been treated, until quite recently, as a poetic convention rather than a scientific claim. People who use the language to describe their suffering are usually understood to be reaching for a metaphor that captures something about the intensity of what they feel.

The peer-reviewed neuroscience of the past two decades has substantially complicated this picture.

What the brain imaging evidence has shown, across multiple research teams, multiple methodologies, and multiple populations, is that emotional pain is not metaphorically similar to physical pain. The two states activate substantially overlapping neural systems, produce substantially similar behavioural and physiological responses, and respond to substantially the same pharmacological interventions. The language of broken hearts and stinging rejection is, on the strongest current reading of the evidence, more literally accurate than the popular framing has assumed.

The 2003 Cyberball study

The foundational peer-reviewed study of the neuroscience of social pain was published in October 2003 by Naomi Eisenberger, Matthew Lieberman, and Kipling Williams in the journal Science. The team designed an experiment to induce social rejection in a controlled laboratory setting while participants were inside a functional magnetic resonance imaging scanner. They used a computer game called Cyberball, in which the participant played a virtual ball-tossing game with what they believed were two other human players. After a brief inclusion phase in which all three players passed the ball to each other, the two other players began passing the ball only to each other, excluding the participant for the remainder of the game.

The two other players were not, in fact, human. They were computer-controlled. The exclusion was a designed feature of the experiment. From the participant’s subjective experience, however, they had just been deliberately excluded from a social activity by two people they had been interacting with moments earlier.

The brain activation pattern during the exclusion phase was the most significant finding of the study. The dorsal anterior cingulate cortex, a region of the brain that processes the affective component of physical pain, was significantly more active during exclusion than during inclusion. The level of activation correlated positively with the participant’s self-reported distress at being excluded. The same region of the brain that becomes active when a person is burned, cut, or struck became active when the same person was ignored in a virtual ball-tossing game.

The Eisenberger team’s interpretation, supported by the subsequent literature, was that the human brain treats social exclusion as a form of injury. The neural alarm system that evolved to alert humans to physical damage to their bodies is, on the available evidence, the same alarm system that alerts humans to damage to their social bonds.

The 2010 Tylenol study

The strongest follow-up evidence for the Eisenberger thesis came from a different direction. In 2010, a team led by Nathan DeWall at the University of Kentucky, with colleagues at Toronto, Florida, UCLA, Florida State, and Georgia College, published a study in Psychological Science that asked a simple question. If social pain and physical pain activate the same neural systems, then a pharmacological intervention that reduces physical pain should also reduce social pain. The team tested this prediction directly.

Participants in the first experiment took either 1,000 milligrams of acetaminophen, the active ingredient in Tylenol and Panadol, or a placebo, every day for three weeks. They reported their daily experience of social pain (feelings of rejection, exclusion, hurt feelings) on a standardised scale throughout the study period. The participants who took acetaminophen reported significantly lower social pain than those who took placebo, with the difference emerging gradually over the three weeks and becoming statistically significant by the end of the study.

The second experiment, also with three weeks of acetaminophen or placebo, used functional magnetic resonance imaging at the conclusion of the dosing period. Participants played the same Cyberball exclusion game while being scanned. The acetaminophen group showed significantly reduced neural activation in the dorsal anterior cingulate cortex and the anterior insula during the exclusion condition, compared with the placebo group. The pharmacological intervention designed to reduce physical pain had reduced both the felt experience and the brain activation associated with social pain.

The finding was substantial. Acetaminophen is one of the most widely used pain relievers in the world, taken by hundreds of millions of people for headaches, muscle aches, fever, and other physical conditions. Its mechanism of action involves central nervous system effects rather than purely peripheral pain blocking, which is the reason it can affect the brain regions that process social pain in addition to the brain regions that process physical pain. The DeWall team noted that this finding has implications for the treatment of social rejection, chronic loneliness, and the social aspects of grief, although they emphasised that acetaminophen is not a recommended long-term treatment for any of these conditions.

The 2011 somatosensory finding

A third major piece of evidence came from a 2011 study by Ethan Kross, Marc Berman, Walter Mischel, Edward Smith, and Tor Wager, published in the Proceedings of the National Academy of Sciences. The Kross team designed the most powerful induction of social pain that had been attempted in a brain imaging study. They recruited 40 participants who had experienced an unwanted romantic break-up within the previous six months and who reported that thinking about their ex-partner still produced significant emotional distress. The participants were placed in an fMRI scanner and shown alternating photographs of their ex-partner and of a familiar but emotionally neutral acquaintance. In a separate task, the same participants experienced a moderate physical pain stimulus, applied as heat to the forearm.

The Kross team found that thinking about the rejecting ex-partner activated not only the affective regions of the brain associated with physical pain, as the Eisenberger team had shown, but also the somatosensory regions, including the secondary somatosensory cortex and the dorsal posterior insula. These are the brain regions that process the felt sensory quality of physical pain, not merely the emotional response to it. The activation pattern in these regions during the romantic rejection condition was 88 per cent predictive of physical pain when compared with a database of more than 500 published pain studies.

The finding moved the science forward in an important way. Until 2011, the strongest interpretation of the Eisenberger data was that social and physical pain shared the affective components but probably not the sensory components. The Kross data suggested that, at sufficient intensity, social pain activates the sensory components as well. The brain of a person looking at a photograph of an ex-partner who has recently rejected them is, on the available evidence, doing something substantially similar to the brain of a person who has been physically burned.

Our team came across an interesting short video that explains the psychology behind what happens when someone has been through too much in life. If this article resonates, it’s worth a watch – click here to view it. 

Why the brain works this way

The current best evolutionary explanation for these findings is that the social attachment system in the human brain piggybacked on the existing physical pain system rather than developing a separate alarm mechanism of its own. Mammalian young, including human infants, require an unusually long period of caregiving to survive. An infant separated from its caregivers will die. The evolutionary pressure to keep infants attached to caregivers, and caregivers attached to infants, has been one of the strongest selection pressures shaping the human brain over the past several hundred thousand years.

The existing physical pain system, which had evolved to register damage to body tissue and motivate behaviour that reduces such damage, was already capable of producing a sufficiently intense aversive signal. The most parsimonious evolutionary solution was to extend this signal to social loss, so that the threat of being separated from social bonds would feel as urgent and unbearable as the threat of physical injury. The result is that the human brain treats damage to relationships, exclusion from social groups, and the loss of attachment figures as variants of the same general category of threat that includes physical wounds.

This explanation, sometimes called the social attachment piggyback hypothesis, has been articulated in detail by Eisenberger in subsequent papers and is the standard evolutionary interpretation of the imaging findings. It is also consistent with the cross-cultural ubiquity of physical pain language in descriptions of social loss. Speakers of unrelated languages, in unrelated cultures, with no shared history of metaphor formation, describe rejection and grief in substantially the same terms. The convergence on physical pain vocabulary appears to be driven by the underlying neural reality rather than by any cultural transmission.

The honest limitations

The social-pain-physical-pain overlap thesis is not, despite the strength of the evidence above, fully settled in the peer-reviewed literature.

A 2014 study by Choong-Wan Woo, Tor Wager, and colleagues, published in Nature Communications, applied a more sophisticated form of brain imaging analysis called multivariate pattern analysis to data on both social rejection and physical pain. The Woo team found that while the same anatomical brain regions are activated by both kinds of pain, the precise neural patterns within those regions are distinct. The brain appears to be using the same general neighbourhood for both kinds of pain, but it is doing different things within that neighbourhood.

The Woo finding does not negate the Eisenberger and Kross results. It does mean that the strongest possible interpretation, in which social and physical pain are essentially the same experience differently triggered, is too strong. The current best reading is that the two kinds of pain share substantial neural infrastructure but are not identical. The overlap is genuine and substantial. The identity claim is too strong on the available evidence.

A separate methodological concern is that the laboratory inductions of social pain, including the Cyberball game and the ex-partner photograph paradigm, are short-duration acute experiences that may not perfectly model the chronic social pain of long-term loneliness, sustained grief, or persistent interpersonal trauma. The neural systems engaged by acute laboratory rejection may differ in important ways from those engaged by months or years of sustained social suffering. The peer-reviewed evidence on chronic social pain is thinner than the evidence on acute laboratory social pain, although the available work suggests broadly similar neural patterns.

What it means

Several things follow from the neuroscience of social pain that are worth saying clearly.

The first is that the popular framing in which emotional suffering is treated as fundamentally different from physical suffering, less real, less serious, less worthy of medical attention, is not supported by the available evidence. The brain treats damage to social bonds as a category of injury and produces a measurable distress signal that overlaps substantially with the distress signal produced by physical injury. The chronic loneliness that the World Health Organization now treats as a global public health concern, the grief that follows the death of a close attachment figure, and the social rejection that produces measurable mortality in long-term studies are all, on the available evidence, registering in the brain as forms of sustained low-grade pain.

The second is that the language people use to describe their emotional suffering is, on the strongest current reading, an accurate report of what is happening rather than a poetic exaggeration of it. A person who describes a breakup as feeling like being punched in the chest is not being dramatic. They are providing the most accurate available verbal description of a neural state that genuinely shares features with being punched in the chest.

The third is that the pharmacological evidence suggests interesting possibilities for the treatment of acute social pain, although the practical implications remain genuinely contested. The DeWall finding that acetaminophen reduces social pain has been replicated and extended in subsequent work, but the long-term implications for grief management, loneliness intervention, and the treatment of attachment-related disorders are not yet established.

The fourth, on the strongest current reading of approximately twenty years of peer-reviewed neuroscience, is that the human capacity for enduring pain extends to the capacity for enduring social pain, because the same neural systems are involved in both, and the same biological constraints determine what can be borne and for how long.

The popular framing has, in a sense, always known this.

The neuroscience is just confirming what every person who has ever lost someone has already been trying to say.

The post Research into the neuroscience of social rejection has shown that the brain regions that activate when a person is excluded, rejected, or grieving a lost relationship are the same regions that activate during physical injury, with the overlap being so substantial that a standard over-the-counter painkiller measurably reduces both kinds of pain, because the human brain has co-opted the physical pain system to register damage to social bonds appeared first on Space Daily.

There is a specific moment, usually in childhood or early adolescence, when most people first hear a recording of their own voice and discover, with mild horror, that it does not sound the way they expected. The voice on the recording is thinner. Higher. More nasal. Less authoritative. Less resonant. It does not seem to match the voice the person has been hearing inside their own head for their entire life. The instinctive reaction is that the recording must be defective somehow — that microphones distort, that playback equipment is poor, that something has gone wrong in the chain between vocal cords and loudspeaker. The recording, in nearly all cases, is fine. The misalignment is between two distinct ways of hearing the same sound, only one of which is available to the listener and only the other of which is available to everyone else who has ever listened to that voice. The recording is a reasonable approximation of the second one. The voice in the speaker’s head is, in important respects, an illusion produced by the speaker’s own skull.

According to a 2023 Mirage News explainer drawing on the underlying acoustics literature, the human auditory system actually has two distinct pathways by which sound reaches the inner ear. The first, called air conduction, is the pathway most people think of as “hearing”: sound waves travel through air, enter the ear canal, vibrate the eardrum, set off a chain of vibrations in the three small bones of the middle ear, and ultimately stimulate the cochlea — the fluid-filled, snail-shaped organ in the inner ear that converts mechanical vibration into the neural signals the brain interprets as sound. The second pathway, called bone conduction, bypasses the outer and middle ear entirely. Vibrations from a sound source travel directly through the bones of the skull — particularly the mastoid and temporal bones near the ear — and reach the cochlea by a structural route rather than an airborne one.

Why bone conduction makes the voice in your head deeper

When a person speaks, the vibration originates in the vocal cords, which sit deep inside the throat, surrounded by skull and jawbone. The sound produced travels outward into the air, where it can be heard by everyone else in the room via ordinary air conduction. But the sound also travels inward, through the bones surrounding the vocal cords, up through the skull, and into the speaker’s own inner ear via bone conduction. The speaker, accordingly, hears their own voice through both pathways simultaneously. Everyone else in the room hears it through only one.

The catch is that bone is not a neutral conductor of sound. As reported by Imperial College London’s coverage of Dr. Tobias Reichenbach’s 2014 research on the mechanics of bone conduction, the bones of the human skull are substantially more efficient at transmitting low-frequency vibrations than high-frequency ones. The bone-conducted version of a person’s voice is therefore weighted toward the lower end of the frequency spectrum — bassier, fuller, and more resonant than the air-conducted version. The voice the speaker hears in their own head is the sum of the air-conducted and bone-conducted versions, with the bone-conducted contribution adding low-frequency depth that no external listener has ever heard. Reichenbach summarised the implication directly in his 2014 paper: “Many of us cringe when we play back a recording of our own voice. This is because we perceive our voice differently to how others hear it. Interestingly, bone conduction plays a role in how we recognise our voice. This is because the process is more effective at transmitting lower-frequency sounds to the brain, which means that we perceive our voice as being deeper than what it is.”

What the recording actually captures

A microphone, sitting in air several feet from the speaker, picks up only the air-conducted version of the voice — the same version that reaches the ears of everyone else within hearing range. When that recording is played back, the listener hears their own voice as it actually sounds to others, without the low-frequency bone-conducted overlay that has, until that moment, been the only version of their voice they have ever known. The mismatch is real, well-characterised, and produces a specific psychological phenomenon that auditory researchers refer to as “voice confrontation” — the sense of cognitive dissonance that accompanies hearing one’s own recorded voice for the first time.

Per an explainer from ENT and Allergy Associates on the phenomenon, the voice-confrontation effect tends to be most pronounced in people who have rarely or never heard recordings of themselves. It also tends to diminish, somewhat, with repeated exposure — singers, podcasters, broadcasters, and others who routinely listen to their own recorded voices gradually adjust their internal voice-image to better match the external reality. But the underlying physical mismatch never goes away. As long as a person has a skull and intact bone conduction, they will hear their own voice with low-frequency emphasis that no one outside their body can detect. The mental image of one’s own voice, accumulated over a lifetime of speaking and listening simultaneously, is structurally different from the voice that anyone else has ever encountered.

The thing humans never heard until 1877

Per Today You Should Know’s overview of the air-conducted versus bone-conducted distinction, one of the historically interesting features of this whole phenomenon is that humans never actually heard the “external” version of their own voice until the late 19th century. Thomas Edison’s phonograph, invented in 1877, was the first technology that could capture sound and play it back — and was, accordingly, the first technology that could ever show a person what they actually sounded like to other people. For approximately 200,000 years before Edison, every member of the species had a mental image of their own voice that was systematically different from the voice that everyone they had ever spoken to had heard. The internal voice was the only voice anyone had ever experienced from inside their own head. The discrepancy was undetectable, and presumably did not exist as a recognisable phenomenon.

The first generation of phonograph users would, by all available historical accounts, have been the first humans in history to experience voice confrontation. The experience has since become a routine part of growing up in any technologically modern society — the moment when a child first hears themselves on a voicemail, or a recording from school, or a video clip, and registers, with confusion, that the voice on the playback does not match the voice they have been hearing inside their own head for as long as they have been speaking. The cognitive adjustment that follows is the small but real psychological work of integrating the external version of oneself into the internal model. For most people, the external version will always sound slightly off. The internal version — fuller, deeper, more resonant — is the version constructed by a brain that has spent its entire life listening to itself through the bones of its own head, with no one else ever in a position to compare notes.

The post Your own voice sounds different to other people than it sounds to you, because the version you hear is reaching your inner ear partly through the bones of your skull, which amplify lower frequencies that everyone else cannot hear — and the recorded version that strikes most people as alien when they first hear it is in fact the only version of their voice anyone else has ever known appeared first on Space Daily.

The story begins in Taiwan in the early 1980s, where roughly 10 to 15 percent of school-age children were nearsighted. By the year 2000, the figure among older teens had risen to approximately 84 percent. No human population can shift its genetic profile by a factor of seven in less than two decades. Something else was happening to children’s eyes, and a generation of ophthalmologists has spent the intervening 25 years trying to figure out what. The current best understanding, drawn from systematic reviews of more than 145 studies involving over 2 million participants worldwide, is that the prevalence of myopia — the technical term for nearsightedness, in which the eyeball grows slightly too long during childhood and distant objects no longer focus properly on the retina — is rising at a rate that has no parallel in any other documented condition of vision or physical development. By 2050, on the available projections, slightly more than half of the entire human population will be affected.

According to the Brien Holden Vision Institute’s summary of its 2016 paper in Ophthalmology, the projected global myopia rate will rise from approximately 28 percent in 2010 to approximately 52 percent in 2050 — meaning nearly 5 billion myopic people by mid-century, with roughly 1 billion of them at significantly elevated risk of permanent blindness due to high myopia (defined in the Holden paper as -5 diopters or worse), a more severe form of the condition that increases lifetime risk of retinal detachment, glaucoma, macular degeneration, and cataracts. The findings have since been confirmed and extended by multiple subsequent systematic reviews, most recently a 2025 meta-analysis in the British Journal of Ophthalmology covering global prevalence trends in children and adolescents from 1990 to 2050.

What is actually happening inside the eye

Myopia is, fundamentally, a problem of axial length. The human eye works by focusing incoming light onto the retina at the back of the eyeball. If the eyeball is too long relative to the focusing power of the cornea and lens, the focal point falls in front of the retina rather than on it, and distant objects appear blurry. The condition is typically progressive during childhood and adolescence — the eyeball continues to elongate as the child grows, and the degree of myopia worsens — before stabilising sometime in early adulthood. Once the eye has elongated, the change is structural and effectively permanent. Glasses, contact lenses, and laser refractive surgery can compensate for the optical consequences, but the underlying eyeball remains longer than it would have been in an unaffected individual, with the lifelong elevation in retinal disease risk that comes with it.

The biological mechanism connecting environmental factors to eyeball elongation has been substantially worked out over the past two decades. As reported by Scientific American’s review of recent myopia research, exposure to natural daylight stimulates the release of dopamine in the retina, and retinal dopamine inhibits the axial elongation of the developing eye. Children who spend substantial time outdoors during the critical developmental years — roughly ages 6 to 12 — receive sufficient daylight exposure to maintain dopamine release and keep eyeball growth on a normal trajectory. Children who spend most of their waking hours indoors, in artificial lighting that is typically one to two orders of magnitude dimmer than natural daylight, receive insufficient stimulation of retinal dopamine, and the eye grows longer than it would otherwise.

The two-factor model

Per a peer-reviewed PMC review of the global myopia epidemic, the strongest predictors of myopia onset and progression in children are two specific environmental factors operating in tandem. The first is reduced outdoor time, which limits the dopamine-mediated protection against eyeball elongation. The second is increased near-focus work — reading, writing, screen-based learning, and recreational device use — which forces sustained accommodation of the eye at close distances and appears to contribute independently to axial elongation. The two factors are partly correlated (children who spend more time on near work typically spend less time outdoors) but operate through separable biological mechanisms. A 2018 Canadian study found that each additional hour per week of outdoor time reduces a child’s odds of developing myopia by approximately 14 percent. A separate Chinese cohort found that children with little daylight exposure have approximately 5 times the myopia risk of well-exposed peers, rising to 16 times the risk when low daylight exposure is combined with heavy near-work activity.

The genetic contribution to myopia is real but limited. Children with one or two myopic parents do have elevated risk, and several genetic variants associated with eyeball geometry have been identified. But the timescale of the global increase rules out genetics as the primary driver. The human gene pool has not changed in any meaningful way over the past 50 years. The myopia rate has, in many populations, tripled or quadrupled over the same period. The environmental contribution must therefore account for the great majority of the recent shift, with genetics modulating individual susceptibility rather than driving the population-level trend.

What the COVID years showed

The pandemic lockdowns of 2020-2021 functioned, inadvertently, as a large natural experiment in the link between indoor time and myopia development. As documented by a 2026 Optometry Times review of the global myopia trajectory, large-scale Chinese cohort studies during the lockdown period reported mean myopic shifts of up to -0.30 diopters within just a few months of confinement — substantially faster progression than the same children would have experienced under normal conditions. The effect was most pronounced in children aged 6 to 8, the age window during which the developing eye appears to be most sensitive to environmental input. The lockdown data essentially closed the remaining scientific debate about whether outdoor time and near work were causally related to myopia or merely correlated. The natural experiment produced exactly the prediction that the environmental hypothesis had been making for years.

What can be done

The interventions that have shown the most consistent effects in randomised trials and population-level programmes are also the simplest. Taiwan, which had the world’s most acute childhood myopia epidemic in the late 20th century, has since 2010 mandated that primary-school students spend at least two hours per day outdoors, with measurable effects on school-age myopia rates. Singapore has implemented similar programmes. Several jurisdictions are now prescribing low-dose atropine eye drops to children showing early myopic progression, which has been shown to slow axial elongation by approximately 50 percent over multi-year follow-up. Orthokeratology contact lenses and specialised multifocal lenses can also slow progression. The most effective single intervention, by every available measure, remains the simplest: getting children outdoors, in natural daylight, for at least an hour or two per day, during the years when their eyes are still forming. The biological logic is straightforward. The cultural logic — getting children to put down screens and spend time outside — has, in most modern environments, turned out to be substantially harder than the biology suggested it should be.

The post By 2050, more than half of the world’s population is projected to be myopic — needing glasses or contacts to see clearly at a distance — according to a series of international vision studies, in a shift driven not by genetics but by the amount of time children now spend indoors and the relative absence of time spent focusing on the horizon during the years when the eye is still forming appeared first on Space Daily.

A child born this year will, by the time they reach late middle age, almost certainly live in a world where the human population is no longer growing. By the time that same child reaches retirement, the population will, on the available projections, have begun to shrink. This is not a fringe demographic claim. It is the central finding of the most recent set of population projections published by the United Nations Department of Economic and Social Affairs, released on World Population Day in July 2024. The report, drawing on data from 1,910 censuses across 237 countries and territories, projects that the global population will peak at approximately 10.3 billion people in the mid-2080s, plateau briefly, and then decline to approximately 10.2 billion by the year 2100. The peak is now expected slightly earlier and slightly lower than the 2022 projections suggested, primarily because fertility rates in several large countries — China most prominently — have fallen substantially faster than demographers had anticipated.

According to the UN’s official World Population Prospects 2024 Summary of Results, the probability that the global population will peak within the current century is now estimated at approximately 80 percent — up substantially from the roughly 30 percent the UN was estimating in 2013. The shift reflects a steady accumulation of evidence over the past decade that fertility rates worldwide are declining faster than mid-twentieth-century demographers had expected. The global fertility rate now sits at approximately 2.25 children per woman, just above the replacement level of 2.1 needed to maintain a stable population. The global rate is projected to cross below replacement in approximately 2036 — within the next decade — at which point the only thing keeping the human population growing will be the demographic momentum of large existing cohorts of young adults still in their reproductive years.

What the country-level data show

The aggregate global figures conceal an extraordinary divergence across countries. Per Population Connection’s analysis of the 2024 UN projections, the populations of 63 countries had already peaked before 2024 — including China, Germany, Japan, Italy, and South Korea — and are now in active decline. An additional 48 countries are projected to peak between 2025 and 2054, covering approximately a tenth of the current world population. Among the lowest fertility rates currently recorded are South Korea at approximately 0.7 children per woman, Hong Kong at 0.8, Taiwan at 0.9, Singapore at 1.0, and China at 1.0 — figures so far below replacement that, absent immigration, these populations will halve every 35 to 50 years on current trajectories. Japan, Italy, and Spain sit at approximately 1.2. Most of Eastern Europe, Northeast Asia, and Southern Europe is now well below 1.5.

At the other end of the distribution, the countries with the highest current fertility rates are concentrated in sub-Saharan Africa. Niger has the world’s highest rate at approximately 6.6 children per woman, followed by Somalia (~6.0), Chad (~5.9), Mali (~5.7), the Democratic Republic of Congo (~5.4), and Nigeria (~5.0). Sub-Saharan Africa as a whole is projected to add approximately 1 billion people by 2054 — accounting for essentially all of the remaining global population growth through the century. The combination of rapid decline in most of the world and continued growth in Africa means that the demographic composition of the species is shifting substantially. By 2100, more than 40 percent of children under five globally will be African, compared to approximately 25 percent today.

Why the trajectory is hard to reverse

The features of the demographic transition that make it particularly difficult to undo were laid out in detail by the UN demographers in their 2024 report. As reported by the French National Institute of Demographic Studies (INED) in its summary of the UN findings, for the 24 countries already at ultra-low fertility with peaked populations, the probability of fertility rates returning to 2.1 or higher within the next 30 years is approximately 0.1 percent — essentially zero. The reason is structural rather than cultural. By the late 2030s, half of the women in those countries will be too old to have children by natural means. Even if pro-natalist policies somehow succeeded in raising the per-woman fertility rate substantially, the absolute number of women in their childbearing years will have contracted so much that total births would continue to fall. The demographic momentum runs in both directions: just as a large cohort of young adults can sustain population growth even at sub-replacement fertility, a small cohort of young adults will produce population decline even if individual fertility rates rise.

The countries that have implemented serious pro-natalist policies — South Korea, Hungary, Singapore, China, Japan — have, to date, produced essentially no measurable effect on fertility rates. Cash payments, parental leave extensions, childcare subsidies, fertility treatment coverage, and direct propaganda campaigns have all been tried, and the rates have continued to fall. The reasons are debated. Most demographers attribute the decline to some combination of education and labour-market participation by women, the rising direct and opportunity costs of raising children in high-income economies, urbanization, housing costs, the prevalence of contraception, changing cultural expectations about parenthood, and the broader transition of children from economic assets to economic costs that has characterised industrialised societies since the mid-twentieth century.

What the end of growth means

As discussed in Population Matters’ overview of the 2024 UN projections, the implications for the structure of human societies are substantial and not yet well-absorbed by most economic and political institutions. By 2080, people aged 65 and older will outnumber children under 18 globally. By the mid-2030s, people aged 80 and over will already outnumber infants worldwide. The age structure of the species is inverting in real time, with consequences for labour markets, pension systems, healthcare infrastructure, military demographics, real estate markets, and essentially every institution that was designed for an expanding population. Immigration will become the primary driver of population growth in approximately 52 countries through 2054 — including the United States, Canada, Australia, and the United Kingdom — meaning the political contests around immigration will, for most of the rest of the 21st century, become inseparable from the demographic survival of the receiving societies.

The Black Death, in the 14th century, was a brief and catastrophic event that killed an estimated 30 to 60 percent of the European population within a few years. The current demographic shift is the opposite kind of phenomenon — slow, voluntary, distributed across decades, and the product of billions of individual decisions about when and whether to have children. The Black Death population decline lasted approximately 150 years before growth resumed. The current decline, on the available projections, has no clear end date in view. Some recent research — notably by the demographer Dean Spears at the University of Texas — argues that the UN projections themselves still overestimate future fertility, and that the global peak may come as early as 2061 at approximately 9.5 billion, rather than the 10.3 billion the UN models project. Whether the peak arrives in 2061 or 2084, the basic direction of the trajectory is no longer in serious dispute among demographers. The era of sustained human population growth — which produced essentially all of the institutional infrastructure of modern civilisation — is ending. The next several centuries will be the first sustained test of how human societies function when the species is contracting rather than expanding.

The post Within the lifetime of children being born today, the global human population is projected to begin shrinking for the first time since the Black Death — no country on Earth currently has a fertility rate above 7 children per woman, and dozens of high-income nations have fallen below 1.5 — in a civilizational shift that demographers now expect to end the era of sustained population growth that has defined humanity for the past several thousand years appeared first on Space Daily.

The popular framing of human evolution, repeated across textbooks, museum exhibits, and most contemporary writing on the subject, is that the human brain has been getting larger across the entirety of our evolutionary history. The story typically begins with the early hominins of approximately 6 million years ago, whose brains were comparable in size to those of modern chimpanzees, and proceeds through a series of steady increases in cranial capacity that culminated in the modern human brain, which is approximately three to four times larger than that of our earliest hominin ancestors and proportionally larger than that of any other primate.

The story is broadly correct for the first 5.99 million years of human evolution. It is, on the strongest current reading of the peer-reviewed evidence, wrong for the most recent chapter.

The average modern human brain is approximately 8.5 per cent smaller than the average late Pleistocene human brain, the difference is real and has been documented repeatedly across nearly ninety years of independent peer-reviewed research, and no one in the relevant scientific disciplines has yet been able to establish either when exactly the reduction occurred or what caused it.

A ninety-year-old observation

The first peer-reviewed observations that modern human brains were smaller than the brains of late Pleistocene humans were published in the 1930s and 1940s by Gerhardt von Bonin (1934) and Franz Weidenreich (1946), both working with the limited cranial samples available at the time. The observation was not initially considered controversial. The data was thin, the methodology was crude by modern standards, and the finding sat quietly in the background of physical anthropology research for several decades.

The observation began to attract more sustained attention from the 1970s onward, as larger cranial datasets became available and as better statistical methods for analysing them were developed. Phillip Tobias published comparative measurements in 1971. Maciej Henneberg, an Australian biological anthropologist who has spent his career studying global cranial datasets, published a series of papers from 1988 onward documenting the reduction across multiple population samples on multiple continents. By the early 2000s, the basic empirical claim that the modern human brain is smaller than the late Pleistocene human brain had been documented in approximately nineteen independent peer-reviewed studies, spanning samples from Europe, Africa, East Asia, Australia, and the Americas.

The average reported reduction across these studies is approximately 8.5 per cent. The late Pleistocene average, on the largest available compilations, was approximately 1,458 cubic centimetres. The modern average sits closer to 1,300 to 1,350 cubic centimetres. The difference of approximately 150 cubic centimetres is roughly the volume of a tennis ball.

The reduction is, in evolutionary terms, surprisingly large. Average hominin brain size increased by approximately 70 cubic centimetres per 100,000 years across the long arc of the Pleistocene, between approximately 800,000 years ago and 30,000 years ago. The Holocene reduction has occurred at a rate that is, depending on how the timing is set, between thirty and one hundred times faster than the earlier increase. In evolutionary terms, the human brain has been shrinking with unusual rapidity by the standards of its own previous trajectory.

The 2021 DeSilva analysis

In October 2021, a team led by Jeremy DeSilva at Dartmouth College, with collaborators James Traniello at Boston University, Alexander Claxton at Oklahoma State University, and Luke Fannin at Dartmouth, published a study in Frontiers in Ecology and Evolution that attempted to identify the precise timing of the brain-size reduction. The team compiled a dataset of 985 cranial measurements from across the full hominin fossil and recent human record, ranging from approximately 9.8 million years ago to the present, and applied a statistical method called change-point analysis to identify the moments at which the rate of brain-size change shifted.

The analysis identified three significant change points in hominin brain evolution. Two were positive, corresponding to known periods of brain-size expansion approximately 2.1 million years ago (coinciding with the early evolution of the genus Homo) and approximately 1.5 million years ago (coinciding with the appearance of Homo erectus and the development of more sophisticated stone tool industries). The third change point was negative. The DeSilva team’s analysis dated it to approximately 3,000 years ago.

The proposed timing was a substantial departure from earlier estimates, which had placed the reduction anywhere from 35,000 to 10,000 years ago. The 3,000-year figure placed the brain reduction in a period of well-documented human history, after the development of agriculture, after the emergence of the earliest cities, and during the rapid expansion of literate societies in the Bronze Age. The DeSilva team’s interpretation, drawn from a comparative analysis of brain evolution in ant species with similar social structures, was that the reduction reflected the externalisation of cognitive load into social structures, the distribution of knowledge across literate groups, and the consequent reduction of selective pressure on individual brain size.

The hypothesis was provocative. It also, the team acknowledged in the paper, depended on the specific timing they had identified, which depended in turn on the specific statistical method they had applied to the specific dataset they had compiled.

The 2022 critique

In July 2022, Brian Villmoare at the University of Nevada Las Vegas and Mark Grabowski at Liverpool John Moores University published a peer-reviewed critique in the same journal. The Villmoare and Grabowski analysis reexamined the DeSilva dataset and identified what the authors considered substantial methodological problems with the original conclusion.

The first issue was sample distribution. The DeSilva dataset of 987 skulls was heavily weighted toward modern samples, with more than half of the specimens dating from the most recent 100 years of the 9.8-million-year time range. The 23 critical specimens from the period in which the brain reduction was supposed to have occurred were drawn from geographically heterogeneous locations, including England, China, Mali, and Algeria. Villmoare and Grabowski argued that this heterogeneity made the dataset unsuitable for detecting a fine-grained change point, because population-level variation between regions was being conflated with temporal variation across the species.

The second issue was the change-point methodology itself. Villmoare and Grabowski reanalysed portions of the same dataset using independent statistical methods and were unable to reproduce the 3,000-year change point. Their analysis found no statistically significant brain-size reduction during the time frame DeSilva had identified. The Villmoare and Grabowski conclusion was that the alleged reduction either did not occur, or that the available data was insufficient to demonstrate it.

The Villmoare and Grabowski critique did not reject the entire 90-year-old observation that modern brains are smaller than late Pleistocene brains. Their argument was specifically that the dramatic 3,000-year reduction the DeSilva team had proposed was not supported by the evidence, and that any actual reduction was likely to have occurred over a much longer time scale and through different mechanisms than the social-evolution hypothesis required.

The 2023 response

In 2023, the DeSilva team published a response to the Villmoare and Grabowski critique, also in Frontiers in Ecology and Evolution. The response acknowledged some of the methodological concerns raised in the 2022 paper and presented a revised dataset that addressed several of them. The revised dataset removed juvenile Neanderthal specimens that had been accidentally included in the original compilation, removed a duplicated entry, and dropped data from the historically problematic Morton collection. The revised dataset also added additional Pleistocene specimens to address the under-sampling concern.

The DeSilva team’s reanalysis with the revised dataset, they argued, still detected a statistically significant brain-size reduction in the recent Holocene. They acknowledged that the exact timing was uncertain and could reasonably be placed anywhere between approximately 5,000 and 3,000 years ago, but they maintained that the broader pattern of reduction was robust. The response also emphasised that the underlying observation, that modern human brains are smaller than late Pleistocene brains, was supported by approximately nineteen independent studies over nearly ninety years and could not reasonably be dismissed even if the specific 3,000-year timing was challenged.

The Villmoare and Grabowski position is that the brain may have reduced more gradually since the origin of Homo sapiens approximately 300,000 years ago, or may not have reduced at all in any statistically defensible sense. The DeSilva position is that a rapid Holocene reduction is real and recent. The dispute is genuinely ongoing in the peer-reviewed literature.

Why the brain might have shrunk

The peer-reviewed literature has produced at least six major hypotheses for why human brain size might have decreased in the Holocene, none of which has won scientific consensus.

The first is the social externalisation hypothesis advanced by DeSilva and colleagues. Cognitive load, on this view, has been progressively distributed across literate populations, writing systems, oral traditions, and social structures, reducing the selection pressure on individual brain size.

The second is the body-size hypothesis. Human body size has reduced measurably during the Holocene, possibly as a result of dietary changes following the agricultural transition, and brain size and body size are known to be correlated in mammals. On this view, the brain reduction is a passive consequence of overall body-size reduction. The Villmoare and Grabowski critique points out that body-size reduction can only account for a small fraction of the observed brain-size reduction, and that other factors must be involved.

The third is the agricultural diet hypothesis. The transition to grain-based diets, which began approximately 12,000 years ago in different regions, reduced overall nutritional quality compared with the hunter-gatherer diet that preceded it. Brain tissue is metabolically expensive to maintain, and reduced nutritional intake may have produced selection pressure for smaller brains.

The fourth is the self-domestication hypothesis. Multiple peer-reviewed analyses have argued that humans have undergone a process of self-domestication during the Holocene, with measurable reductions in aggression-related neural systems and corresponding changes in facial structure. Domesticated animals consistently show brain-size reductions of approximately 10 to 15 per cent compared with their wild ancestors, and the human brain reduction may reflect the same mechanism.

The fifth is the energetic efficiency hypothesis. Smaller brains may have been selected for because they require less metabolic energy to operate. The human brain consumes approximately 20 per cent of total body energy, and even modest reductions in brain size can produce substantial energy savings that may have been advantageous under conditions of dietary stress or population pressure.

The sixth is the cognitive efficiency hypothesis, distinct from but related to the social externalisation argument. On this view, the human brain has not become less capable but has become more efficient, with the same cognitive functions implemented in a smaller volume through changes in neural organisation, white-matter density, or synaptic efficiency.

The hypotheses are not mutually exclusive, and most researchers in the field accept that some combination of factors is probably responsible. The disagreement is about which factors matter most and how they interact.

The honest limitations

Several methodological caveats apply to the literature described above.

The first is that cranial capacity is an indirect proxy for brain size, not a direct measurement of it. The brain does not fill the entire cranial cavity, and the relationship between endocranial volume and actual brain mass varies between populations and individuals. The Holocene reductions identified in the literature are based on cranial measurements, not direct brain measurements, and the relationship between the two is not entirely settled.

The second is that the available fossil and recent human cranial samples are not evenly distributed across time, geography, or population. The Pleistocene samples come from a relatively small number of well-preserved individuals from specific regions. The Holocene samples come from much larger numbers of individuals from much wider geographic and population coverage. Comparing the two requires statistical adjustments that involve assumptions about how representative each sample is, and different researchers have made different assumptions.

The third is that the relationship between brain size and cognitive ability is not direct. Larger brains do not, on the contemporary evidence, reliably produce greater intelligence within or between populations. The Holocene reduction, even if real, does not necessarily indicate that modern humans are less intelligent than late Pleistocene humans. The relationship between brain volume and cognitive function is mediated by neural organisation, connectivity, and efficiency in ways that volume measurements cannot capture.

What it means

Several things follow from the brain-shrinkage evidence that are worth saying clearly.

The first is that the popular framing of human evolution as an ongoing march toward larger brains is not supported by the most recent peer-reviewed data. The available evidence, on the strongest current reading, indicates that the human brain has been shrinking, slowly, for somewhere between 3,000 and 300,000 years. The standard textbook narrative of ever-expanding cranial capacity ends approximately 30,000 years ago, in the late Pleistocene, when the maximum average human brain size was reached. Everything since has been a slow contraction.

The second is that the cause of the reduction is genuinely unknown. At least six major peer-reviewed hypotheses are currently in active scientific competition, and the dispute about which one is correct, and whether the reduction occurred 3,000 years ago or 30,000 years ago or across the whole Holocene, is one of the more interesting open questions in physical anthropology.

The third is that the finding sits uncomfortably with the broader cultural narrative about human progress. The 3,000-year time frame that DeSilva proposed, in particular, coincides with the rise of writing, the emergence of cities, the development of complex political institutions, and the cumulative cultural achievements that most accounts of human history treat as the defining markers of advancement. If the DeSilva interpretation is correct, the average human brain has been getting smaller throughout the entire period of recorded civilisation, and the cause may be the very social and technological developments that civilisation is usually understood to consist of.

The fourth, on the strongest current reading of nearly ninety years of peer-reviewed evidence, is that the human brain may be getting smaller because we no longer need it to do quite as much as it once had to.

The peer-reviewed scientific literature has not yet established whether this is true.

It is, however, on the strongest available evidence, not impossible.

The post The average human brain volume has decreased by approximately 150 cubic centimetres since the late Pleistocene, equivalent to roughly the volume of a tennis ball, in a finding documented across nearly ninety years of peer-reviewed physical anthropology research, with no agreed scientific explanation for why one of the most distinctive evolutionary trends of our species has reversed appeared first on Space Daily.