r/paleoanthropology

Paper: https://www.science.org/doi/10.1126/science.aed8437

A team of researchers from the University of Sydney and the University of Glasgow argues that dietary sugars, not animal foods, may have played the decisive role in the expansion of the human brain over the past 4 million years, as hominin brain size grew nearly fivefold, from about 300 grams in early relatives like Australopithecus afarensis to roughly 1,500 grams in modern Homo sapiens.

Their findings offer a different perspective on the longstanding scientific view that meat consumption was a key driver of human evolution.

Neanderthals may have trekked deep into the deserts of the Arabian Peninsula around 55,000 years ago, a new study of stone tools suggests.

The study focused on stone tools discovered at Jebel Katefeh-1 (JKF-1), an archaeological site beside an ancient lake near the city of Jubbah, in Saudi Arabia's Nefud Desert (also spelled Nafud or An Nafūd). No Neanderthal bones have ever been found in Arabia, so researchers wondered who was making tools there

A repeatedly heated patch of clay, fire-damaged tools and locally rare pyrite form the earliest convincing archaeological case for deliberate fire-making, although no human remains identify the makers directly

New research suggests that no matter what we eventually determine the last common ancestor of humans and chimpanzees to be, we'll learn it was a primate that climbed trees.

Researchers observed and confirmed with measurements that wild sooty mangabey monkeys in an Ivory Coast forest display foot bone flexibility that facilitates vertical climbing up skinny tree trunks to hide, forage or sleep.

Study: https://doi.org/10.1073/pnas.2608183123

Link to Paper: https://www.biorxiv.org/content/10.64898/2026.08.07.743438v1

Two leg bones dredged from the seafloor west of Taiwan are beginning to fill in the Denisovan silhouette. And, boy, are they revealing! According to a yet-to-be-peer-reviewed analysis of the remains, Denisovans were absolutely enormous by the standards of ancient humans.

One individual may have stood close to 1.9 meters, or 6 feet 3 inches, and weighed about 91 kilograms (around 200 lbs). The other was roughly 1.8 meters tall and weighed about 83 kilograms.

Both were probably male, judging from their sizes, though the researchers could not determine their sex molecularly.

Both Denisovans would have been unusually large even beside Homo sapiens living in East Asia around the same time: a roughly 40,000-year-old modern human from Tianyuan, China, stood about 1.7 meters and weighed around 73 kilograms, the researchers mention in their study.

The genomic evidence also suggests some genetic contact with populations farther north. Although the Jomon show stronger overall ancestry associated with a southern migration route into East Asia, researchers detected a subtle genetic contribution from northern Upper Paleolithic Siberian groups.

This finding is broadly consistent with archaeological evidence showing similarities between blade-based stone technologies in prehistoric Japan and those found farther north in Eurasia.

The study also provides new insight into prehistoric population changes in Hokkaido. The researchers conclude that later Hokkaido Jomon were not direct descendants of the Upper Paleolithic inhabitants of the island.

Instead, genetic evidence supports a population replacement in which Jomon groups originating in Hondo—the main Japanese islands excluding Hokkaido—moved north during the Holocene.

One of the study’s most significant findings concerns adaptation to cold environments.

The Jomon carried relatively high frequencies of genetic variants associated with nonshivering thermogenesis—the body's ability to generate heat without muscular shivering—and with the perception of cold. These include variants involving UCP1 and TRPM8.

A subgroup of Early Holocene Nile Valley foragers displays unusual bony labyrinth morphology and congenital inner ear-specific pathological changes consistent with possible syndromic conditions. This may result from several demographic scenarios, including prolonged endogamy and geographic isolation under environmental constraints.

Comparative data from the Horn of Africa and Central Africa reveal high morphological diversity, suggesting strong population substructure and dynamic demographic trajectories during the Holocene.

These findings provide rare insights into prehistoric population structure in the region, and demonstrate the usefulness of bony labyrinth morphology where ancient DNA is unavailable.

Paper Link: https://www.nature.com/articles/s41598-026-59915-8

https://www.iflscience.com/men-evolved-a-unique-pelvis-that-puts-a-spring-in-their-step-but-women-have-the-same-pelvis-as-neanderthals-84306

Surprisingly, the pelvis of Neandertal males shares more features with the human female pelvis than with the human male pelvis. Many of the differences between the Neandertal male pelvis and that of the Homo sapiens male seem to stem from the unusual anterior position of the acetabula (hip joints) in H. sapiens males and the subsequent increase in the horizontal anteroposterior distance between the joint and the line of gravity.

The forward migration of the hip joints transforms the modern human male pelvis into a shock-absorbing device that cushions the drop of the center of mass with every step and at the same time stores potential energy in the flexor muscles of the thigh, causing the pelvis to bounce back.

The thickening of the ramus and the ensuing modifications are a response to the increased adductor force required on the pubic side to counterbalance the larger moment generated by the longer body-weight lever arm on the opposite side of the hip joint fulcrum.

The shock-absorbing device seems to benefit modern males, mainly in long-distance walking

https://preview.redd.it/akbx1lw4p4jh1.png?width=940&format=png&auto=webp&s=27dd3375b2ae5ac600ef116e0cc6368609028e04

In1953 Dart claimed that discoveries of primitive hominins in South Africa over the previous thirty years had demonstrated that **"**the loathsome cruelty of mankind to man forms one of his inescapable characteristics and differentiative features". He built that bad news story from finding that (a) his small-brained australopithecus had lived in an environment where abundant predators and prey set a high standard both in killing and avoiding being killed (b) The australopiths had small canines, especially compared with the canines that made associated baboons formidable (c) The australopiths bipedal posture allowed them to carry weapons. He put those together with the observation that weapons are what humans use in loathsome cruelty to each other.

I must admit that I'm invested in Dart's story. He was a cultural hero of my childhood and the most famous professor in the university where I later trained as a land surveyor. It seems to me much more important that humans are descended from Australopiths than from their ancestral chimps or bonobo.

Anyway, Dart's story can be used with modern data to make the good news that the human future is the opposite of inescapable; it's created open-endedly from a need to predict and control the future of the group. The modern data I'm talking about is presented in in DeSilva et al. (2021) "When and Why Did Human Brains Decrease in Size? A New Change-Point Analysis and Insights From Brain Evolution in Ants" https://www.frontiersin.org/journals/ecology-and-evolution/articles/10.3389/fevo.2021.742639/full

DeSilva and his colleagues were interested in an apparent rapid decrease in human brain size just over the last 3000 years. But to reveal that recent trend they fitted a chain of linear trend lines to hominin brain capacity measurements over the last 10 million years. Their algorithm identified change-points marked up as CP1 CP2 and CP3 in the graph I, that I cropped from their figure 1.

Dart's Taung Child, dated at 2.6Ma, was close to the sharp change point CP1 and it marks a more dramatic change than graph I shows. DeSilva et al. used a vertical scale of Log10(cc), without explaining that choice. If they had instead directly used their raw cc data, the trend line from Miocene Apes to CP1 would have looked more horizontal, making the CP1 nick point look even more distinct.

The existence of CP2 might even be an artifact of their choice of a log scale. Graph II projects the CP1-CP2-CP3 lines as blue curves in a (cc vs time) space. The straight red line shows that CP2 would then lie much closer to C1-CP3 than in Figure I. Figure III trials the opposite projection of a hypothetical straight line CP1-CP3 from cc-vs time space onto a log scale space, revealing a curve that bulges upwards, somewhere along which their change point algorithm would locate CP2.

If one takes CP2 out of the figure then their graph would have a hockey stick shape, with CP1 as a nick point where the Environment of Evolutionary Adaptiveness (the modern equivalent of Dart's highveld biome) changed abruptly from one uniform and long-lasting EEA to another uniform and persistent one.  That EEA2 involved a more than 10 times increase in cranial expansion rate, from about 24cc/My to 330cc/My.  It was the second EEA, that Dart saw as involving offensive hunting and warring, that drove encephalization.

Dart was wrong to see relationships between hominin groups as analogous to those between predators and prey. Predators simply need their prey's protein while their prey need to keep that for themselves. Both are involved in game theory's "game against nature".  But game theorists are mainly interested in "games" between actors who have incomplete information about the intentions of an equal "Other".  

DeSilva et al. bring a useful insight into who exactly these game-theory "actors" were, by classifying humans as a eusocial species, analogous to ant and termite colonies. They proposed that a recent decrease in human brain size was enabled by eusocial species offloading individual cognitive demands, maybe with the advent of writing ca. 5000 years ago.  They were writing before the era of LLM-based AI, which would give urgency to their argument. But anyway, they didn't try to explain how eusocial behaviour might have evolved in humans, when it's rare amongst mammals; they cite only the weak equivalents of Damaraland and Saharan mole-rats.

It's natural to ask how humans might have become eusocial in the first place, and what brain expansion had to do with that. And it's tempting to invent a Just-So Story about a pivotal "aha" event of a hominin encountering "Man Friday" from another group.  But we are on more familiar ground if we consider the relations faced by an armed hominin group 1.5Ma, hemmed in by adjacent groups, when predators no longer restricted their daytime foraging or nighttime refuge availability. That is shown by the ancestors of Ho floresiensis having reached Indonesia by the same time, across a wide variety of biomes.  

Each adjoining troop would present a range of potential future interactions in many dimensions, including one ranging from indifference ("good fences make good neighbors") to the most horrific and consequential war. It would have been adaptive for the troop to have been of one mind about what could be in the mind of Other troops, what their relative capacities are, and what to do about that.  

In modern humans this cultural motivation for the way forward is achieved through language but the Oxford anthropologist Robin Dunbar has argued that within-troop information could have originally been broadcast through public enactment without necessarily involving speech, but rather, through dramatic mime: stories are motivational structures of meaning, vocabulary and syntax evolved as refining explorations, which natural selection is supremely good at.

Dunbar's thesis came from the opposite direction than Darts; he saw proto-language emerging from social grooming rather than social imperatives. But if his sequence is right and if eusocial behavior is maintained though language, then humans don't seem condemned by their inherited inescapable characteristics, but rather we are enabled by having inherited an ability to model and construct our future.

PS. After I post this, I'm going to give it to Claude for comment. I expect it will open its response with a more complimentary remark than you might make. Then it will raise some points that a reader will balk at, and offer to fix it. Too late for that. But I'd like to hear what a human thinks.

Afterward it seems pretty obvious that homo massively expanded its range, reduced predation to at least modern chimpanzee levels and lower and spread the Stone Age culture globally.

But before that, given discoveries in the survival of non-Homo hominins deeper into the evolution of the homo lineage and the gigantic Pongo relative we know little about in Asia.

Do you think Homo might have been a side story if we could time travel back 2.4 million years?