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Homo naledi’s small but sophisticated brain challenges belief in “an inevitable march towards bigger, more complex brains.”

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Naledi brains, at 1/3 size, had human-like features/John Hawks

From ScienceDaily:

The recently-discovered species Homo naledi may have had a pint-sized brain, but that brain packed a big punch. New research by Ralph Holloway and colleagues — that include researchers from the University of the Witwatersrand, Johannesburg, South Africa — published in the Proceedings of the National Academy of Sciences examines the imprints of the brain upon the skulls of this species, called endocasts. The research highlights the humanlike shape of naledi’s tiny brain, surprising scientists who studied the fossils. These findings draw further into question the long-held belief that human evolution was an inevitable march towards bigger, more complex brains.

Naledi lived in southern Africa about southern Africa between 236,000 and 335,000 years ago, originating at the same time as modern humans, according to current dating.

The anatomy of naledi’s frontal lobe was similar to humans, and very different from great apes. Naledi wasn’t alone. Other members of our genus, from Homo erectus to Homo habilis and the small-brained “hobbits,” Homo floresiensis, also share features of the frontal lobe with living humans. But earlier human relatives, like Australopithecus africanus, had a much more apelike shape in this part of the brain, suggesting that functional changes in this brain region emerged with Homo. “It’s too soon to speculate about language or communication in Homo naledi,” said coauthor Shawn Hurst, “but today human language relies upon this brain region.”

The back of the brain also showed humanlike changes in naledi compared to more primitive hominins like Australopithecus. Human brains are usually asymmetrical, with the left brain displaced forward relative to the right. The team found signs of this asymmetry in one of the most complete naledi skull fragments. They also found hints that the visual area of the brain, in the back of the cortex, was relatively smaller in naledi than in chimpanzees — another humanlike trait.

The small brains of Homo naledi raise new questions about the evolution of human brain size. Big brains were costly to human ancestors, and some species may have paid the costs with richer diets, hunting and gathering, and longer childhoods. But that scenario doesn’t seem to work well for Homo naledi, which had hands well-suited for toolmaking, long legs, humanlike feet, and teeth suggesting a high-quality diet. According to study coauthor John Hawks, “Naledi’s brain seems like one you might predict for Homo habilis, two million years ago. But habilis didn’t have such a tiny brain — naledi did.”

The researchers seem to be looking for something that nature seems not to provide: an ape-like missing link. They probably cannot accept that such a being may not exist any more than physicists and chemists centuries ago could conceive of a universe that didn’t need ether or phlogiston. Don’t expect them to give up the search any time soon.

See also: At Aeon: Homo naledi buried dead which suggests that maybe humans are not special, of course


Homo naledi had sophisticated but small brain

4 Replies to “Homo naledi’s small but sophisticated brain challenges belief in “an inevitable march towards bigger, more complex brains.”

  1. 1
    polistra says:

    It’s odd… After 60 years of experience with electronic intelligence, where smaller and simpler means you can pack more memory and functions into the same box, we still make the opposite assumption about wetware.

    Most of the cortex is associative axons, not neuron cell bodies, so (within limits) a smaller cortex means faster associations across the axons. At some point the total number of neurons creates a limit, but that’s a broad range.

  2. 2
    OLV says:

    You may laugh at my dumb question, but that’s fine.
    They seem to explain it in the paper, but I don’t quite get it. How do they know the complexity of the brain by the shape of the skull?

  3. 3
    bornagain77 says:

    Contested Bones (by Christopher Rupe and John Sanford) is the result of four years of intense research into the primary scientific literature concerning those bones that are thought to represent transitional forms between ape and man. This book’s title reflects the surprising reality that all the famous “hominin” bones continue to be fiercely contested today – even within the field of paleoanthropology.

    Chapter 10 (Homo naledi – “Almost Human” or Fully Human?) – video

    Chapter 4 (Homo Erectus – Upright “Ape-man” or Fully Human?) – video

    Chapter 8 (Homo habilis – Crucial “Missing Link” or Invented Species?) – video

    Chapter 5 (Homo floresiensis – Is “Hobbit” a new species?) – video

    Chapter 6 (Australopithecus afarensis – Full Story About “Lucy”) – video

    If Modern Humans Are So Smart, Why Are Our Brains Shrinking? – January 20, 2011
    Excerpt: John Hawks is in the middle of explaining his research on human evolution when he drops a bombshell. Running down a list of changes that have occurred in our skeleton and skull since the Stone Age, the University of Wisconsin anthropologist nonchalantly adds, “And it’s also clear the brain has been shrinking.”
    “Shrinking?” I ask. “I thought it was getting larger.” The whole ascent-of-man thing.,,,
    He rattles off some dismaying numbers: Over the past 20,000 years, the average volume of the human male brain has decreased from 1,500 cubic centimeters to 1,350 cc, losing a chunk the size of a tennis ball. The female brain has shrunk by about the same proportion. “I’d call that major downsizing in an evolutionary eyeblink,” he says. “This happened in China, Europe, Africa—everywhere we look.”

    Scientists Discover Proof That Humanity Is Getting Dumber, Smaller And Weaker By Michael Snyder, on April 29th, 2014
    Excerpt: An earlier study by Cambridge University found that mankind is shrinking in size significantly.
    Experts say humans are past their peak and that modern-day people are 10 percent smaller and shorter than their hunter-gatherer ancestors.
    And if that’s not depressing enough, our brains are also smaller.
    The findings reverse perceived wisdom that humans have grown taller and larger, a belief which has grown from data on more recent physical development.
    The decline, said scientists, has happened over the past 10,000 years.

    Human Genetic Variation Recent, Varies Among Populations – (Nov. 28, 2012)
    Excerpt: Nearly three-quarters of mutations in genes that code for proteins — the workhorses of the cell — occurred within the past 5,000 to 10,000 years,,,
    “One of the most interesting points is that Europeans have more new deleterious (potentially disease-causing) mutations than Africans,”,,,
    “Having so many of these new variants can be partially explained by the population explosion in the European population. However, variation that occur in genes that are involved in Mendelian traits and in those that affect genes essential to the proper functioning of the cell tend to be much older.” (A Mendelian trait is controlled by a single gene. Mutations in that gene can have devastating effects.) The amount variation or mutation identified in protein-coding genes (the exome) in this study is very different from what would have been seen 5,000 years ago,,,
    The report shows that “recent” events have a potent effect on the human genome. Eighty-six percent of the genetic variation or mutations that are expected to be harmful arose in European-Americans in the last five thousand years, said the researchers.
    The researchers used established bioinformatics techniques to calculate the age of more than a million changes in single base pairs (the A-T, C-G of the genetic code) that are part of the exome or protein-coding portion of the genomes (human genetic blueprint) of 6,515 people of both European-American and African-American decent.,,,

    Genetic Entropy – peer reviewed references!properties/ctzx

  4. 4
    vmahuna says:

    OLV @ 2

    The general pattern is that more complex brains gain more “folds” on the outer surface. Human brains are covered with nooks and crannies. The nooks and crannies leave signatures on the inside of our skulls. Simpler animals have brains whose surface is completely smooth.

    For comparison, elephants and whales have HUGE brains by weight and volume. But there is no evidence that blue whales are 100 times as intelligent as humans. Although there is the argument that the fact that whales aren’t interested in talking with humans is a sure sign of the whales’ high intelligence.

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