Introducing the brain: human chimp brain comparison (Introduction)

by David Turell , Monday, September 05, 2022, 15:46 (810 days ago) @ David Turell

Little gene differences but large brain differences:

https://mindmatters.ai/2022/08/researchers-find-more-ways-that-human-and-ape-brains-dif...

"After grouping cells with similar expression profiles they revealed 109 shared primate cell types but also five that were not common to all species. These included a type of microglia, or brain-specific immune cell, that was present only in humans and a second type shared by only humans and chimpanzees.

"The human-specific microglia type exists throughout development and adulthood, the researchers found, suggesting the cells play a role in maintenance of the brain upkeep rather than combatting disease… An analysis of gene expression in the microglia revealed another human-specific surprise — the presence of the gene FOXP2. This discovery raised great interest because variants of FOXP2 have been linked to verbal dyspraxia, a condition in which patients have difficulty producing language or speech.

***

"...chimpanzees, our closest living relatives, have brains that are one-third the size of our own, although they are very similar to us in body size. Most of this brain-size difference reflects the evolutionary expansion of the association cortex, a group of regions that supports such sophisticated cognitive functions as language, self-awareness, and problem solving.”

"Human brains are especially asymmetric. “Researchers compared geometric differences between brain scans of humans and chimpanzees. They observed structural asymmetries in both human and chimpanzee brains, but human brains were especially asymmetric.”

"The human brain allocates more cells to thinking skills. “… a part of the brain called the cerebral cortex – which plays a key role in memory, attention, awareness and thought – contains twice as many cells in humans as the same region in chimpanzees.”

"Our brains have many more language connections. “Especially the fasciculus arcuatus, a bundle of connective nerve fibres important for the processing of language, is connected to many more areas in humans than in macaques, and even in chimpanzees.”

"There are distinct differences at the molecular and genetic level. “Specifically, the researchers’ results showed that interneurons expressing genes that code for dopamine synthesis are present in humans’ striata but not in non-humans’. This, they say, is part of what makes human brains uniquely human. Neuromodulatory transmitters, in particular dopamine, are involved in distinctly human aspects of cognition and behavior, such as working memory, reasoning, reflective exploratory behavior, and overall intelligence” (my bold)

"The Smithsonian National Museum of Natural History tells us that “While the genetic difference between individual humans today is minuscule – about 0.1%, on average – study of the same aspects of the chimpanzee genome indicates a difference of about 1.2%. The bonobo (Pan paniscus), which is the close cousin of chimpanzees (Pan troglodytes), differs from humans to the same degree. The DNA difference with gorillas, another of the African apes, is about 1.6%. Most importantly, chimpanzees, bonobos, and humans all show this same amount of difference from gorillas. A difference of 3.1% distinguishes us and the African apes from the Asian great ape, the orangutan.”

"The differences between our brains and those of primates seem to be much greater than the genetic differences, so they don’t seem to originate in the genes. The mystery is perhaps analogous to that of the human mind."

Comment: The problem of gene comparison has been explained here in the past. It is gene 3-D relationships that make the differences. It is estimated with 3-D relationships we differ from chimps by 21%.