Footsteps into the Future

This post was started Jul 13th, 2019

I am going to use this posting to gather some notes about evidence of selective sweeps in the human genome, which is to say evolutionary processes.  There are a few caveats assocciated with this posting.  One is that it operates on the assumption that human evolution is an ongoing process (I would say at the Hand of God).  Another is that it skirts around the subject of eugenics, which is rife (Rife! I tell you) with both classical and christian hubris.  Being a romantic, I deny any association with the eugenicists.  When the time comes for "natural" (or otherwise) selection within the human race, I prefer the hand of God.

I will add to the discussion of "selective sweeps" some of my own speculations about how changes in medical expertise may also have an eventual impact on our genomes, assuming that there is any normality in the ways that our genomes change or are edited in the future.  We may already be a long ways past the usual understanding of Natural Selection when we talk about the human genome.  I strongly distinguish between selective sweeps that may be permanently incorporated into the human population genome and selective sweeps resulting from external agents such as infectious diseases.

So here are a few interesting links from Wikipedia:

• ASPM (gene) 
• DAB1 (among Chinese) 
• SV2B (among African Americans) 
• Selective sweeps In humans (more generic) 
• Microcephalin (potentially introgressing from non-modern human race) 

Here is a link to a document that identifies many genes (potentially?) subject to selective sweeps.  I cannot vouch for the accuracy of this document since I am out of my depth here.

http://pages.cs.wisc.edu/~peicheng/newVersion/pdfs/plosGenetics2007.pdf

The examination of human genetics is rife (rife! I tell you) with various pitfalls, not so much when it is used to examine differences between the races as when it is used to assign value to those differences (a subtle distinction).  It is likely that other genes are undergoing selective sweeps.  Many of those sweeps may turn out to be related to population replacement events (the euphemism for massacres/genocides) rather than more subtle selective pressures on population genetics.

Geneticists are always suspect from a political viewpoint for this reason (the assignment of "value") and also because they have been associated with the eugenics document "The Geneticist's Manifesto" written by Hermann Muller in 1939.  As you may guess there were a lot of things wrong with the timing and the politics.  It is hard to find a copy of this document online, perhaps because it is still under copyright protection, and also possibly because no one would consider it politically correct since WWII stamped out Aryanism  for a generation.

I have a few comments about the Manifesto:

1. I have a copy which, as usual with learned documents, I have not carefully read.  I could scan it and put it online but I fail to find the motivation since it may be a copyright violation.
2. Leonard Darwin (Charles's son) at the age of 89 wrote an article for Nature magazine in 1939 about the manifesto, an article which he also called "The Geneticist's Manifesto".  It was only a review of Muller's manifesto without much discussion of the contents of the manifesto.  Note that he pretty much endorsed the manifesto and that he was a known eugenicist (and military man).
3. The manifesto was written before the existence of the gene as a physical entity was demonstrated by the description of the DNA molecule in 1953.  In those days the "gene" was purely a hypothesis of Mendelian science experiments.  In Charles Darwin's world there was no rigorous science of inheritance (Mendelian or otherwise) at all, only ad hoc observation.  This means, in the light of current science, that Charles Darwin was all but prophetic - along with the malarial fever dreams of Wallace.
4. In 1939 it might have been possible to form some clumsily obvious goals (smarter? tamer?} for a eugenics program.  In our era things are not so clear cut and I can see many problems for a nation that attempts to enforce genetic conformity or even just to offer a genetic standard as a so-called "improvement".  We do see some efforts with regard to certain obviously harmful genetic diseases.  This seems reasonable but nothing is certain.  Deaf people are now organizing against treatment since eliminating deafness will also eliminate their unique culture.
5. We live in a time when genetics may become "fashion".  It is possible that "fashion" will lead us into all the same problems that the disgraced science of eugenics might have given us.  Even now people in India and China are adjusting the sex ratio of their populations in ways that may lead to disaster (or perhaps merely to extreme weirdness).

So now we come to my own observations about trends in human evolution.  One obvious adaptation would be either cultural or physiological resistance to birth control.  The Catholic church is the most obvious cultural example.  If we suppose that Darwin was right and that the failure to reproduce is one way to limit the presence of a gene line in the future, it is pretty clear that the future belongs, paradoxically, to the Mormons et al..  It may also belong to those unable to grasp the complexities of birth control, but there is a lot more to raising kids than giving birth.  As for physiological resistance to birth control I see a variety of mechanisms to accomplish that, some of which are probably already at work.

One other major change in culture, at least in developed countries, is the prevalence of caesareans as a way of giving birth.  It is estimated that something like thirty percent of the births in the United States are by caesarean section.  Caesareans happen for many reasons, but one factor is the size of the baby's head at birth.  When I worked in the X-ray department at Community Memorial Hospital in Ventura, California, one of the procedures that we regularly performed was a "pelvimetry".  There would be an image of a baby's head fully engaged in a woman's pelvis.  Measurements would help to determine whether it was going to work or not.

At one time, many women died in childbirth (and there were many reasons for that).  At least one reason was that the baby's head was too large to pass the birth canal.  The incidence of caesareans removes that constraint to the tune of some value less than thirty percent of all births.  In evolutionary terms this is huge.  In usual evolutionary processes the selective pressure may be as little as .1 percent or less.  It acts over time, over many generations.

If the current rate of caesareans continues for as long as ten generations. I predict that few women will be able to give birth normally and that the human race will embark on a new wave of selective sweeps based on the lack of a constraint on the size of a baby's head at birth.

 Selective Sweeps due to Disease

What the Lord giveth can also be taken away.  I consider disease related selective sweeps to be contingent on the ongoing pressure from the disease.  This is especially true since there is often a price paid in genetic fitness for the benefit of resistance to infectious disease.  A classic example is genetic resistance to malaria.  Malaria is a big deal, which is under a steady attack from the Bill & Melinda Gates Foundation, but is still a big killer around the world.  HIV-1 resistance is also found in a small proportion of certain western populations.  That is guessed to be the result of infectious disease-related selective sweeps.  The sweeps were not driven by HIV since that disease entered human populations relatively recently.  It takes a relatively strong sweep to get to 10% (heterozygous) frequency in the short estimated time since the origin of the gene (~2k years before present).  With the extinction of Smallpox and HIV we could expect a reverse sweep on this allele since it carries significant drawbacks in terms of other diseases (such as West Nile virus and tick-borne encephalitis).