Human evolution; how DNA changed from Chimps (Introduction)

by David Turell , Saturday, January 14, 2023, 21:34 (457 days ago) @ David Turell

Has to do with HAR areas in DNA:

https://phys.org/news/2023-01-evolution-uniquely-human-dna.html

"Humans and chimpanzees differ in only one percent of their DNA. Human accelerated regions (HARs) are parts of the genome with an unexpected amount of these differences. HARs were stable in mammals for millennia but quickly changed in early humans. Scientists have long wondered why these bits of DNA changed so much, and how the variations set humans apart from other primates.

"Now, researchers at Gladstone Institutes have analyzed thousands of human and chimpanzee HARs and discovered that many of the changes that accumulated during human evolution had opposing effects from each other.

"This helps answer a longstanding question about why HARs evolved so quickly after being frozen for millions of years," says Katie Pollard, Ph.D., director of the Gladstone Institute of Data Science and Biotechnology and lead author of the new study published today in Neuron. "An initial variation in a HAR might have turned up its activity too much, and then it needed to be turned down."

***

"More recently, Pollard's group wanted to study how human HARs differ from chimpanzee HARs in their enhancer function. In the past, this would have required testing HARs one at a time in mice, using a system that stains tissues when a HAR is active.

"Instead, Whalen input hundreds of known human brain enhancers, and hundreds of other non-enhancer sequences, into a computer program so that it could identify patterns that predicted whether any given stretch of DNA was an enhancer. Then he used the model to predict that a third of HARs control brain development.

"'Basically, the computer was able to learn the signatures of brain enhancers," says Whalen.

"Knowing that each HAR has multiple differences between humans and chimpanzees, Pollard and her team questioned how individual variants in a HAR impacted its enhancer strength. For instance, if eight nucleotides of DNA differed between a chimpanzee and human HAR, did all eight have the same effect, either making the enhancer stronger or weaker?

***

"The idea that HAR variants played tug-of-war over enhancer levels fits in well with a theory that has already been proposed about human evolution: that the advanced cognition in our species is also what has given us psychiatric diseases.

"'What this kind of pattern indicates is something called compensatory evolution," says Pollard. "A large change was made in an enhancer, but maybe it was too much and led to harmful side effects, so the change was tuned back down over time—that's why we see opposing effects."

"If initial changes to HARs led to increased cognition, perhaps subsequent compensatory changes helped tune back down the risk of psychiatric diseases, Pollard speculates. Her data, she adds, can't directly prove or disprove that idea. But in the future, a better understanding of how HARs contribute to psychiatric disease could not only shed light on evolution, but on new treatments for these diseases.

"'We can never wind the clock back and know exactly what happened in evolution," says Pollard. "But we can use all these scientific techniques to simulate what might have happened and identify which DNA changes are most likely to explain unique aspects of the human brain, including its propensity for psychiatric disease."

Comment: I've presented HAR's in the past. I view this as a peek into how God programmed us.