Summary: A new study links genes that pose as a risk factor for autism and schizophrenia with genes that influence the ability to communicate during development.
Source: George Washington University.
A new study challenges the belief that human tooth size decreased and brain size grew at similar rates through our evolution.
A new study from the George Washington University’s Center for the Advanced Study of Human Paleobiology (CASHP) found that whereas brain size evolved at different rates for different species, especially during the evolution of Homo, the genus that includes humans, chewing teeth tended to evolve at more similar rates. The finding suggests that our brains and teeth did not evolve in lock step and were likely influenced by different ecological and behavioral factors.
This research challenges the classically accepted view that reduction of tooth size in hominins is linked with having a larger brain. The reasoning is that larger brains allowed hominins to start making stone tools and that the use of these tools reduced the need to have such large chewing teeth. But recent studies by other authors found that hominins had larger brains before chewing teeth became smaller, and they made and used stone tools when brains were still quite small, which challenges this relationship.
The new study evaluates this issue by measuring and comparing the rates at which teeth and brains have evolved along the different branches of the human evolutionary tree.
“The findings of the study indicate that simple causal relationships between the evolution of brain size, tool use and tooth size are unlikely to hold true when considering the complex scenarios of hominin evolution and the extended time periods during which evolutionary change has occurred,” said Aida Gómez-Robles, lead author of the paper and a postdoctoral scientist at GW’s CASHP.
To conduct the research, Dr. Gómez-Robles and her colleagues analyzed eight different hominin species. The researchers identified fast-evolving species by comparing differences between groups with those obtained when simulating evolution at a constant rate across all lineages, and they found clear differences between tooth evolution and brain evolution. If the classical view proposing co-evolution between brains and teeth is correct, they expected to see a close correspondence between species evolving at a fast rate for both traits. The differences they observed indicate that diverse and unrelated factors influenced the evolution of teeth and brains.
“Once something becomes conventional wisdom, in no time at all it becomes dogma,” said Bernard Wood, university professor of human origins at GW and a co-author of the paper. “The co-evolution of brains and teeth was on a fast-track to dogma status, but we caught it in the nick of time.”
About this evolution research article
Source: Emily Grebenstein – George Washington University Image Source: NeuroscienceNews.com image is credited to George Washington University. Original Research:Abstract for “Brain enlargement and dental reduction were not linked in hominin evolution” by Aida Gómez-Robles, Jeroen B. Smaers, Ralph L. Holloway, P. David Polly, and Bernard A. Wood in PNAS. Published online January 3 2017 doi:10.1073/pnas.1608798114
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[cbtabs][cbtab title=”MLA”]George Washington University “Evolution of Brain and Tooth Size Were Not Linked in Humans.” NeuroscienceNews. NeuroscienceNews, 30 January 2017. <https://neurosciencenews.com/brain-dental-evolution-5850/>.[/cbtab][cbtab title=”APA”]George Washington University (2017, January 30). Evolution of Brain and Tooth Size Were Not Linked in Humans. NeuroscienceNew. Retrieved January 30, 2017 from https://neurosciencenews.com/brain-dental-evolution-5850/[/cbtab][cbtab title=”Chicago”]George Washington University “Evolution of Brain and Tooth Size Were Not Linked in Humans.” https://neurosciencenews.com/brain-dental-evolution-5850/ (accessed January 30, 2017).[/cbtab][/cbtabs]
Brain enlargement and dental reduction were not linked in hominin evolution
The large brain and small postcanine teeth of modern humans are among our most distinctive features, and trends in their evolution are well studied within the hominin clade. Classic accounts hypothesize that larger brains and smaller teeth coevolved because behavioral changes associated with increased brain size allowed a subsequent dental reduction. However, recent studies have found mismatches between trends in brain enlargement and posterior tooth size reduction in some hominin species. We use a multiple-variance Brownian motion approach in association with evolutionary simulations to measure the tempo and mode of the evolution of endocranial and dental size and shape within the hominin clade. We show that hominin postcanine teeth have evolved at a relatively consistent neutral rate, whereas brain size evolved at comparatively more heterogeneous rates that cannot be explained by a neutral model, with rapid pulses in the branches leading to later Homo species. Brain reorganization shows evidence of elevated rates only much later in hominin evolution, suggesting that fast-evolving traits such as the acquisition of a globular shape may be the result of direct or indirect selection for functional or structural traits typical of modern humans.
“Brain enlargement and dental reduction were not linked in hominin evolution” by Aida Gómez-Robles, Jeroen B. Smaers, Ralph L. Holloway, P. David Polly, and Bernard A. Wood in PNAS. Published online January 3 2017 doi:10.1073/pnas.1608798114