Bigger brains led to bigger bodies in our ancestors

Bigger brains led to bigger bodies in our ancestors
New research shows that a strong selection to increase brain size alone played a large role in both brain- and body-size increases throughout human evolution. This phenomenon also may have been solely responsible for the major increase in both traits that occurred during the transition from human ancestors like Australopithecus, a model of which is seen here in the American Museum of Natural History's Hall of Human Origins, to Homo erectus. Credit: © AMNH/R. Mickens

New research suggests that humans became the large-brained, large-bodied animals we are today because of natural selection to increase brain size. The work, published in the journal Current Anthropology, contradicts previous models that treat brain size and body size as independent traits responding to separate evolutionary pressures. Instead, the study shows that brain size and body size are genetically linked and that selection to increase brain size will "pull along" body size. This phenomenon played a large role in both brain- and body-size increases throughout human evolution and may have been solely responsible for the large increase in both traits that occurred near the origins of our genus, Homo.

"Over the last four million years, and increased substantially in our ," said paper author Mark Grabowski, a James Arthur postdoctoral fellow in the Division of Anthropology at the American Museum of Natural History. "This observation has led to numerous hypotheses attempting to explain why observed changes occurred, but these typically make the assumption that brain- and body-size evolution are the products of separate forces."

That assumption is now being questioned, based on a large body of work that has shown that genetic variation—the fuel of evolution—in some traits is due to genes that also cause variation in other traits, with the result that selection on either trait leads to a correlated response in the unselected trait. Consider the leg bone, or femur, of an elephant. As the bone gets longer, it also gets wider. If artificial selection is used to produce a tall elephant, its legs likely won't just become long, they'll also get wider. Part of this effect is due to shared genetic variation, or covariation, among traits in the femur. Grabowski set out to explore this kind of genetic relationship between human brain size and body size, and its impact on our evolution.

With brain- and body-size covariation patterns from a range of primates and modern humans, Grabowski created a number of models to examine how underlying genetic relationships and selection pressures likely interacted across the evolution of our lineage. His findings demonstrate, for the first time, that strong selection to increase brain size alone played a large role in both brain- and body-size increases throughout . This phenomenon also may have been solely responsible for the major increase in both traits that occurred during the transition from human ancestors like Australopithecus (the most famous of which is the Lucy fossil) to Homo erectus.

In other words, while there are many scientific ideas explaining why it would be beneficial for humans to evolve bigger bodies over time, the new work suggests that those hypotheses may be unnecessary; instead, body size just gets pulled along as the brain expands.

"While selection no doubt played a role in refining the physical changes that came with larger body sizes, my findings suggest it was not the driving force behind body-size evolution in our lineage," Grabowski said. "Therefore, evolutionary models for the origins of Homo based on an adaptive increase in body size need to be reconsidered."

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More information: Mark Grabowski. Bigger Brains Led to Bigger Bodies?: The Correlated Evolution of Human Brain and Body Size, Current Anthropology (2016). DOI: 10.1086/685655
Journal information: Current Anthropology

Citation: Bigger brains led to bigger bodies in our ancestors (2016, April 18) retrieved 16 October 2019 from
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Apr 19, 2016

Ever time you post you are exposing your stupidity and ignorance for all to see. Of course you are too dumb to know that.

Apr 19, 2016
'Rather, they should start with some ** DUST **, and see it if makes sense that life arose from non-life. See if this process can be repeated. See if any such magical events ** 6000 years ago ** really is practical.'

Apr 19, 2016
Bart ... You are full of it. In this case I am not sure what It is but you have It in abundance.

Your world view is to complain about people that start with an idea that has been tested by others and see what they can glean from it about other specific things.

Whereas you start from a book that has ideas that have not been tested and cannot be tested. And you don't want to see what other ideas can be gleaned from it because the exploration of ideas starts and ends with that same particular book.

You have no idea what evolution actually is despite commenting on it endlessly. I really would like to see you open your eyes, but I think you are so far down a blind alley that you think it is better to keep going into the darkness rather than turn around and head towards the light of understanding.

Apr 19, 2016
"an understanding of evolution has been instrumental to developments in numerous scientific and industrial fields, including agriculture, human and veterinary medicine, and the life sciences in general". [ https://en.wikipe...volution ]

@GU: I'm not sure if you are addressing science or religion, since a prominent religion is said to call for a magic event of life appearing out of dust 6 kyrs ago.

To be clear, evolution is not tested by emergence of life, since it differs from "differential reproduction", it is rather 'production'. As it happens we now know that evolution goes all the way back, cells have inherited ~ 20 traits from the Hadean geological environment that life emerged in ~ 4 billion years ago.


Apr 19, 2016

[If anyone is interested, the vent theory is the strongest theory. All the known stumbling blocks has been solved in it during the last two years.

The coup de grace: latest it could be demonstrated that early genes - functional RNA strands - segregates by functionality in vent pores. That means expression, cooperation and selfish competition among genes, exactly as we see in today's genomes, and together with the encapsulating pores all the prerequisites for evolution.

In fact, I know of only two should-be-trivial missing chemical synthesis steps out of roughly 20 between Hadean H2&CO2 and RNA. With those emergence of life would have been demonstrated in principle - of course you won't test a 10 - 100 kyrs process in toto as the non-scientists believe will happen. Do we test stellar fusion by making a sun in the lab!? Yet we know how it happens, same as we may soon know for sure in more detail at least one way life can emerge out of geology, not just that it did.]

Apr 19, 2016
[Oops. To be exceedingly pedantic, the missing N2 going into RNA is believed to come from Miller type produced amino acids, which elaborates pentose into nucleobases. Vents have an amazing ability of concentrating organic material many orders of magnitude.

Also, we would know that life emerged out of geology despite the phylogenetic evidence of frozen in traits, because we know early Earth was sterile, then it wasn't. Ergo, geology (Earth) did it.]

Apr 19, 2016
Dinosaurs has relatively tiny brains. Brains grow in accordance with complex action and planning. For past 10000 years man's brain shrinking as his knowledge is outsourced to writing and authorities, allowing him to devolve into more simple organism like VietPet

Apr 20, 2016
Here is the result on nucleotide strand segregation:

"Sorting the wheat from the chaff

... in addition to sorting molecules according to their lengths, temperature differences can also drive sequence-dependent sorting. Both effects are based on the phenomenon of thermophoresis, the differential response of components of molecular mixtures to temperature gradients.

"The separation is so effective that certain types of fragments actually condense into gels when they hybridize with complementary partner molecules. — Even more strikingly, sequences that differ by only a few bases are partitioned into different gels," Mast explains.

[ http://www.astrob...t-chaff/ ]

@kochnik: I think it is 40 kyrs of shrinking; potato, potatoe. But in fact our brains have decreased as our statures did, thanks to the start of agriculture it seems, so it is data in favor of the hypothesis. (I dunno how the recent length increase will affect it.)

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