Thought to be a link between primitive and advanced primates, their fossil skulls were the best evidence available for understanding the neuroanatomy of the earliest ancestors of modern primates. But there was just one problem—the brain cavities of the fragile skulls contained only rock and dust.
The eight virtually reconstructed and dissected brains—the most ever created for a single study—show an evolutionary burst including improved vision and more complex neurological function preceded an increase in brain size, said Harrington, now a Duke University doctoral student. Details of the findings are described online in the Journal of Human Evolution. Top and bottom views, respectively, of the virtual brains of Notharctus tenebrosus A, B, C, E and F , Adapis parisiensis G and H and Smilodectes gracilis bottom two rows within transparent renderings of their skulls.
Arianna Harrington during fieldwork in the badlands of Wyoming. Photo courtesy of Arianna Harrington Scientists have long debated whether primates have always had big brains compared to body size, or if this was a trait that appeared later. Adapiforms, which are not directly related to humans, evolved after the earliest primate ancestors, called plesiadapiforms, which lived about 65 million years ago. This was an awesome overview of the article. Falk's article was incredibly detailed when explaining the different ways brain size can vary. However, I do agree that one of the details they lacked on were what specifically classified as intelligence.
It was kind of implied to be complex social structures, language, and infrastructure. However, it wasn't entirely clear. Thanks for the review Casey. I do appreciate Falk mentioning that these different comparative approaches ie brain size vs reorganization are not mutually exclusive when examining these relationships, nor is one approach "better" than the other in every case.
I believe this speaks to the more holistic, interdisciplinary approach that is emphasized within neuroanthropology. A given method might yield more useful information than another within a specific context. I must admit that the neural reorganization during the evolution of primate brains is a topic that I was not particularly familiar with.
However, this approach could provide very interesting comparative data. Unfortunately, Falk mentions that some of this data may be unavailable to us such as the specifics of the reorganization of brain structures in our recent ancestors. Personally I think this data, should it become available, could be very enlightening. Because what constitutes human consciousness and intelligence, so far as I can understand them, are not the brain structures per se.
Memories are not stored within neurons but are instead the interconnections between the neurons. Large shifts in neural connections or interconnectedness between brain regions could reflect the selective pressures driving brain evolution. After our classroom discussion, I understand a little bit more about how absolute and relative brain size are helpful in understanding primate brain evolution.
Absolute brain size has been shown through the fossil record to have been grown in different primates. However, from our classroom discussion I have realized that relative brain size is more important when looking at primate brain evolution. Though it is not as well recorded in the fossil record because of assumptions about how large the skull is based upon relationships between skeletal structures, relative brain size has increased in primates as well.
Understanding encephalization quotient and reorganization of different brain structure is even harder because we would need soft tissue samples to analyze the differences between ancestral species and current species. However, we can make some assumptions, though not great ones, about reorganization from looking at extant species. The classroom discussion has imbued upon me the importance in taking different aspects of brain size to understand how primate brain evolution has occurred and the why it is important to study non-human primate brain evolution to better understand human brain evolution.
Using comparative approaches, a strong aspect of neuroanthropology, can help us gain an even better understanding of primate brain evolution. This blog is group authored by Dr. RSS Feed.
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To best answer this question, we must study the evolution of the primate brain and the adaptations made early in primate brain evolution and how those early adaptations have influenced brain physiology of primates and humans. This is done by direct and comparative methods. The direct method is to study endocasts, or casts of the interior of braincases. These can be physical, fossilized endocasts and virtual endocasts created by 3DCT data, both allowing for the study of living and extinct species of primates pg. The comparative methods are used to study living species and include histochemical, immunocytochemical, positron emission tomography PET scans, and functional magnetic resonance imaging FMRI scans.
Evolution of the Primate Brain: Size Is Just a Start | Psychology Today
Using these methods, researchers can learn about neurons, including their types, sizes, densities, distributions, and connections, and about functional processing in the brain and how it works in terms of movement, sensation, sleep, preparation for action, thinking, and emotions pg. Apparently, there is some division among paleoanthropologists regarding the importance of absolute brain size and brain reorganization. Specifically, the argument is about which is superior. Falk provides in-depth analysis of both areas.
In the sections devoted to the evolution of primate brain size, Falk discusses how to best interpret primate brain size, which is quite the undertaking due to the wide variation among primates. RBS is a ratio between brain and body size. Falk discusses the methods that comparative studies use to eliminate the effects of allometric scaling on the brain.
Primate mosaic brain evolution reflects selection on sensory and cognitive specialization
It should be noted that EQ heavily depends on the group being studied for baseline data and can easily overestimate the EQ of smaller-bodied species and underestimate the EQ of larger-bodied species pg. It should be noted that both hypotheses do not hold for bats and so their broader application in mammals is questionable. Falk also gives an overview of encephalization in hominins, providing the detailed Table 1 on pages and Few intact femurs of hominins provide few accurate measures for determining body mass and size and therefore RBS.
On page he mentions a study done by Semendegeri which dispels the idea that humans have abnormally large frontal lobes, which are larger due to allometric scaling, not because humans have better cognitive abilities pg.