by Roger Bourke White Jr., for Anthropology 1020, Jennifer Campbell, copyright June 2014
Some people say that when humans start living in prosperous urban lifestyles the pressures of natural selection end. I say, "Hardly! They simply change in which direction they are pushing." The change is dramatic, and that is topic of this reflection.
The huge advances in health care available to humans living in modern civilized conditions is the primary reason people make the assertion that natural selection has stopped. Thanks to modern health care, disease and other lethal conditions no longer take such a fearsome toll on children and reproductive age adults. This assertion is true. But what it means is that good health and a ferociously active immune system are not the centers of selective success that they are in poorer more primitive lifestyles. Selection has not stopped. It has moved on. It is centered on different lifestyle elements.
In the health arena what is selected for instead is humans who don't succumb to the diseases of prosperity such as obesity and diabetes. However, this selection pressure may end soon if we develop cures for these newly emerging health problems as well.
There are many other traits besides health that can be selected for. Here are some other examples.
In Japan, a developed nation with a large urban population, the fertility rate is way below what will keep Japan's population stable. From this 5 Jun 14 The Asahi Shimbun article, Japan’s fertility rate increases slightly, but population still shrinking by Atsuko Hatayama (http://ajw.asahi.com/article/behind_news/social_affairs/AJ201406050062),
"Japan’s fertility rate inched up in 2013, but actual births hit a record low and the number of marriages was the smallest since the end of World War II, a health ministry report showed.
The fertility rate--the number of children a woman is expected to give birth to in her lifetime--was 1.43 for 2013, up 0.02 point from a year earlier, according to the report released June 4.
Although the fertility rate for 2012 also rose slightly, the past two figures were still well below the 2.07 needed to prevent Japan’s population from shrinking."
What is happening here (Roger's hypothesis) is that prosperous urban life offers a lot of distractions to the activity of child making and child raising. Lots of people succumb to these distractions and don't have many children.
In response, if this goes on for many generations, natural selection will select those people who don't get distracted. These are the people who, "Stay on Target!" and have lots of children in spite of the distractions. This will push the human gene pool. It will strongly favor women who get "baby crazy". How it will affect men's thinking is not as clear because in a prosperous lifestyle a women doesn't need a man's close and steady support as much as she does in a primitive lifestyle.
But this "push" is no sure thing because also mixing into this pot is humanity's dramatically increasing skills at manipulating genetics and the birthing and child raising processes. If many clone babies grown in artificial uteruses and raised by robots replace lots of human born-and-raised babies, this selecting pressure for baby crazy women will vanish.
This is a topic I have been interested in for many years. I have given it a lot of thought, and I write about this social context of baby making a hundred years from now in my science fiction book "Child Champs: Babymaking in the year 2112" (Authorhouse, 2012, ISBN 978-1-47725-301-4).
Multi tasking -- the ability to mix various kinds of communications skills with various other kinds of activities -- is a valuable one in our current civilized conditions. We can learn to do this better, as our younger generations are demonstrating. However if the benefits of this skill-set continue on for dozens of generations or more, those brains that pick up hardwiring to do this, and as a result do it better than average, will be selected for.
As with the fertility issues of the previous section, this change will happen only if the pressure goes on for many generations. This is another area of civilized living that can change dramatically and quickly, so how long this selection pressure will last is no sure thing. An example of a skill that has been selected for for about a hundred years in the US, but is about to disappear, is automobile driving skill.
Genetic engineering is going to make a big difference in the speed and direction in which the gene pools drift of all species humans associate with. But it will have limits. It will not do all kinds of changes with equal ease.
Genetic engineering will work best on changing Mendelian traits -- those that have one or just a handful of alleles involved. An example might be fixing the gene for Vitamine C synthesis in humans. Those traits that are affected by large numbers of genes -- such as males successfully getting laid while still a teenager and females successfully marrying doctors -- are going to remain more influenced by breeding than by the efforts of genetic engineers.
--The End--