by Roger Bourke White Jr., copyright July 2006
I read an article in Science News which resonated with some of my thinking about evolution and the human condition.
The article in the June 24, 2006 edition was titled "Older but Mellower" and talked about how neuroscientist Leanne M. Williams of Westmead Hospital in Australia had done some studies of brain changes as a person ages. What she found was that there was an orderly change in how emotion was handled. As a person aged beyond fifty, the processing of viewing pictures of people expressing different emotions shifted between the prefrontal cortex (the very front of the brain) and the amygdala (a part of the central brain). There are a lot of interesting implications to this finding.
One is that the prefrontal cortex is involved in complex cognitive behaviors like sorting through opposing options, ranking things or options, cause and effect relationship, etc. It also is used for decision making, personality expression, and moderating correct social behaviors. In terms of the Brain’s Thinking Stack (covered in the Thinking Stack chapter) this is the Judgment Area. When a child is looking at someone, they are using a lot of judgment thinking. This is why a child stares at interesting faces.
The amygdala, on the other hand, is an emotional center, responsible for processing emotional reactions and forming and storing memories associated with emotional events. Older people process faces and make decisions about them much more quickly—snap judgment. While these are interesting details, what is really neat about this finding is the implications for human natural selection.
What is important for natural selection is that this is an orderly change that the brain undergoes when a person is fifty years old and older. The reason this is important is that it means evolution cares about fifty-year-old humans, cares even though they are no longer having children.
One of the basic premises of evolution is that what matters to the gene pool is survival. Another common premise is that whatever happens to an organism after its children are successfully reared doesn't matter to evolution, and this is why organisms that reproduce sexually age. The premise is that a sexually-reproducing organism trades off in favor of high performance in the growing and reproducing years and doesn't care about what happens after that. That "doesn't care" condition is aging.
In the case of humans, this premise about sexually-reproducing organisms not caring what happens to old members of the species appears to have been modified. It now seems that how grandpa's brain is organized affects how well grandson survives. This appears to be so because the brains of old people undergo a well-organized, and standardized, transition. This means that this transition is something programmed into human genes. And if it's programmed into human genes, it means it has been selected for, which means it matters to human survival.
The sins of the father may be visited on the sons, but the benefits of a good-thinking grandfather also bring blessings to the grandson.
The change in thinking is substantial in the sense that it is moving from one place in the brain to another distant place, which means that evolution has been working on this change a long time. This means that the change was beneficial to early Stone Age humans who lived tens of thousands of years ago, not just historical humans who lived five thousand years ago. It is likely that this ability to reorganize thinking was encouraged by the development of strong language skill, because that's the vital skill in allowing a grandfather to influence a grandson's survival. And this reorganizing of thinking would have enhanced the value of language skill.
It is truly impressive that evolution could pick up on such a subtle benefit -- grandparents being helpful to grandchildren in how they think -- and find a way to organize the gene pool to pass the benefit on through many generations.
Update: This 8 Sep 12 article, Female sexuality: Tunnel of love, brings up a converse example -- one where it seems evolution doesn't care. This article is a review of the book "Vagina: A New Biography." by Naomi Wolf. In it she relates, "It turns out that she needed spinal surgery. The female pelvic neural network is surprisingly complex, she learns; more so than men’s. The neural pathways that connect a woman’s clitoris, vulva and vagina to the spinal cord—and from there to the brain—are unique to every woman."
If this is true (the source is not authoritative) it implies that how this connection is made is as not important to Mother Nature as the brain evolution talked about above. The connection can be made in many ways, some better, some worse, and all will pass the Grandchild Test. This is a good converse example.
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