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What the small-brained hobbit reveals about primate evolution

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hobbit human primate brain size evolutionIs bigger always better? When it comes to brain size, that has long been the prevailing theory—at least among big-brained humans. But a new analysis shows that in the course of primate evolution, brains and brawn haven’t always been on the rise.

Ever since a petite female Homo floresiensis (or "hobbit") was described in 2004, scientists have been debating whether this recently extinct hominin could have evolved to have such a small noggin or if this specimen—the only one for which a skull has been found—was an aberration.

The Indonesian individual stood at just about one meter high and had a brain about a third the size of modern humans. Despite these striking size differences, some H. floresiensis fossils date to just 13,000 years ago—which means they would have lived alongside brainy humans for some 187,000 years. Some researchers propose that she and her clan were modern descendents of Homo erectus and had devolved to their diminutive stature because they lived on an island (a phenomenon documented in other species known as insular dwarfism) or that her particular errant body and brain size were due to an underlying pathology, such as dwarfism or an oversized pituitary gland.

Others, however, posit that H. floresiensis is from a more primitive lineage and evolved—for whatever reason—to have this smaller brain.

A new study, published online January 26 in the journal BMC Biology, brings some new perspectives to the table, examining size trends in primate evolution and finding that brains and bodies don’t always get bigger over time. 

The researchers, led by Stephen Montgomery of the Department of Zoology at the University of Cambridge in the U.K., studied the brain and body sizes—changes that often go hand-in-hand—of 37 living and 23 extinct primate species. Montgomery et al. found that although "selection has acted to enlarge primate brains, in some lineages this trend has been reversed."

The primate brain, prized for being supersize among mammals, varies greatly today, ranging from the tremendous H. sapiens‘ encephalon, which typically weighs in at about 1,330 grams to the gray mouse lemur (Microbebus murinus), whose brain weighs only about 1.8 grams. And the earliest primates likely had a brain that was a mere 0.12 gram.

The authors found that although the overall trend has been a brainy explosion in primates (an average increase of 2.5 percent each million years), both brains and bodies have diminished in size along many branches of the primate tree. And given these corporeal and cerebral cutbacks, the researchers found that "under reasonable assumptions, the reduction in brain size during the evolution of Homo floresiensis is not unusual in comparison to these other primates," Nick Mundy, also with Cambridge, said in a prepared statement. Given the findings, the researchers concluded, "We should perhaps not be surprised by the evolution of a small-brained, small-bodied hominin."

Image of Homo floresiensis skull [left] and Homo sapiens skull [right] courtesy of Peter Brown/University of New England

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  1. 1. JC+ 8:14 pm 01/26/2010

    Natural selection gives a perfectly rational description of why, how and, in the broadest sense, <i>where</i> this happens. The idea that <i>in time</i> a large-brained species such as ourselves (<i>wise man</i> or "wise guy" as his hairier cousins prefer to call him) may give rise to "pea brain" has a sort of poetic ring of evolutionary satisfaction about it perhaps. [Looking at recent political history has this happened already you may ask ... but I digress.] There is no development from ‘primitive’ to ‘advanced’ – such thinking is the product of a wish to explain why we are so special in creation. The possibility, hard for many to buy, is that we, quite simply, are not guaranteed our ‘place’ any more than was T. Rex.

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  2. 2. jtdwyer 1:57 am 01/27/2010

    While others may disagree, I agree that the only objective to developmental changes is propagation of capabilities that benefit survival of the organism in the then current environment. Otherwise, if a larger brain size is the final objective of development, we should eventually develop gigantism in order to support larger, heavier brains. Of course, that still could happen at some point, given favorable environmental conditions.

    It seems most likely that the `hobbit’ developed in a geographically confined environment, such as an island. This appears to be the case for the development of pygmy mammoths from the much larger standard mammoth. I have not heard of any study to determine how much smaller the brain case of the pygmy mammoth was in comparison to the standard mammoth. It should be instructive to evaluate that relationship both in proportional and absolute terms. There seems to be no evidence that the pygmy variant had diminished mental capabilities.

    It has been speculated that the hobbit must have had diminished intellectual capabilities, but unfortunately no evidence is available. However, it seems possible to me that a proportionately smaller primate could be as intelligent as we are, as long as its brain had proportionately equivalent structural characteristics. Modern humans with essentially the same brain sizes have been shown to have a wide variety of specific intellectual abilities depending on, in some cases at least, structural variations.

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  3. 3. sunnystrobe 11:43 am 01/27/2010

    Why do we ‘homines sapientes sapientes’, super-savvy humans ( by our own nomenclature) tend to subsume that ‘bigger’ is always ‘better’?
    Small Is beautiful! think:ipod, think: Chihuahua!
    The Ice Ages in the northern hemisphere might have made the difference : forcing our forebears to eat meat, a high- calorie diet known to cause rapid growth acceleration- vide the height differences between parent generations and their offspring in Australian migrants!
    Most likely, the Philippines did not undergo any ice ages during the last hundred thousand years!
    For an evolutionary perspective concerning human and pre-human nutrition, see Youthevity.com

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  4. 4. alexoneal 1:30 pm 01/27/2010

    Discussions like this always remind me of Vonnegut’s Galapagos, in which he argues that the current level of intelligence was a disadvantage to humans. And our best friends, the dogs, seem to have done fine with reduced brain size in comparison with their lupine cousins. (Of course, they’re closely allied with us, which may or may not work out for them in the long run.)

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  5. 5. winberly 1:08 am 01/28/2010

    This article seems to over look the importance of the brain mass to body mass ratio…it implies that there is such a correlation, but doesn’t state it clearly enough. If the body mass to brain mass ratio was the same in the "hobbits" as it is in modern humans, then their intelligence levels would be comparable. A smaller brain does not necessarily mean "less intelligent," IF the ratios allow for a relatively large brain. Neanderthals had larger brains, but it is believed that they were comparable in intelligence to modern humans because they also had greater body mass.

    Bigger does not imply "smarter," after all, several species have bigger brains, but it the body mass to brain mass ratio that makes the difference.

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  6. 6. Paul First 12:13 pm 01/28/2010

    In the beginning of the world, God created every species, He not only gave each individual its lifespan, He also gave each species a species lifespan. People like to think that while the earth’ envirement remains suitable for living, every species will be living forever generation after generation untill the world becoming unsuitable for living. That is not true. There is no other reason for dinosaur to disappear from earth than its species lifespan had been fulfilled.Mankind as a species also has its own species lifespan given by God. When human being is nearer to the end of its lifespan, its fertility will drop gradually, male’s sperm will become less and less. Death rate will exceed birth rate, child birth will be rare , population will decrease continuously. When population dropped to a critical point, society will have great change. There will be no enough people to maintain modern civilization. Cities,even nations, will be abandoned one by one. People will probably move to several spots in the world to live together. When population dropped to a very severe point, there will not be enough people to fullfil the division of labour in society, power plants will be stopped, airline, railroad, communication, internet will all be stopped, because there is not enough people to maintain or operate those appliance. When the last person naturally died, human being will bedisappeared from earth. After human being disappeared, other animals whose species lifespan are longer than human being will be multiplied. that will not be known to us

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  7. 7. Paul First 12:40 pm 01/28/2010

    In the beginning of the world, God created every species, He not only gave each individual its lifespan, He also gave each species a species lifespan. People like to think that while the earth’ envirement remains suitable for living, every species will be living forever generation after generation untill the world becoming unsuitable for living. That is not true. There is no other reason for dinosaur to disappear from earth than its species lifespan had been fulfilled.Mankind as a species also has its own species lifespan given by God. When human being is nearer to the end of its lifespan, its fertility will drop gradually, male’s sperm will become less and less. Death rate will exceed birth rate, child birth will be rare , population will decrease continuously. When population dropped to a critical point, society will have great change. There will be no enough people to maintain modern civilization. Cities,even nations, will be abandoned one by one. People will probably move to several spots in the world to live together. When population dropped to a very severe point, there will not be enough people to fullfil the division of labour in society, power plants will be stopped, airline, railroad, communication, internet will all be stopped, because there is not enough people to maintain or operate those appliance. When the last person naturally died, human being will bedisappeared from earth. After human being disappeared, other animals whose species lifespan are longer than human being will be multiplied. that will not be known to us

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  8. 8. PotatoChip 4:01 pm 01/28/2010

    Very nice story.

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  9. 9. Geopelia 8:40 pm 01/28/2010

    13,000 years is near to the start of human civilization. Could legends of the "little people" have been passed down through the generations from that time?
    Perhaps they were these hobbits, rather than the San "Bushmen".

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  10. 10. ColleenHarper 12:45 pm 02/23/2010

    To Paul First:
    It’s nice fiction, but I’m afraid it would not stand up to rigorous scientific examination. Granted, I’m impressed that you have made testable statements and hypotheses that can be invalidated, which is quite uncommon for Intelligent Designers.

    But I’m not convinced. Sorry.

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  11. 11. V L Skjonsby 2:01 pm 04/6/2010

    There are many relict populations around the world from the Negritos in Asia, Bushmen in Africa as examples. Many polynesian groups have stories of the "Menehune" or little people. In Hawaii the first Hawaiians found fish ponds that were ascribed to the menehune. They may have been more widespread than just the island 0f Flores. Why call them Hobbits? Do they have large feet? Do they have hobbit holes?
    I prefer to think of them as the origin of the menehune stories.

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