Biology is not physics: the perils of reasoning a priori

This is just a quick note following from some ideas I read a while back about the impossibility of understanding biological systems by reasoning from first principles. In short, the problem is that living things have a history; they evolved. One cannot simply look at an animal or a biological phenomenon and understand it as if it were a built structure or a fundamental physical process. This is because evolution works with what it has, and uses a lot of “kludges“.

As Nietzsche wrote, in The Genealogy of Morals, “Only something which has no history is capable of being defined.” Living things cannot be defined as if they were abstract constructions.

The perils of bringing the approach of the physicist to understanding biology are well illustrated, in my view, by some of the ideas of Dr Greg Cochran, who was originally a physicist.

Cochran is probably most famous for his idea that homosexuality is caused by a germ. I have no problem with this, in theory. But in practice, as I have noted here, there is a much simpler explanation that would occur to someone who understood fully that mammals develop in utero and that things often go wrong during this process (that is, there is more to individual animals than genes under selection).

In my opinion, Cochran has done it again with his latest arguments that the gene for white skin in northern Europeans probably has to do with something other than increasing vitamin D production in low ultraviolet conditions, the traditional explanation (see the reference to Nina Jablonski’s work in the comments on my post here).

He does not completely discount the traditional vitamin D hypothesis, but he thinks that that cannot be the main reason for the skin whitening mutation to have spread, because “The various sweeping alleles that have made Europeans and North Asians have light skin were not favored because they helped you garner extra vitamin D, at least not mostly. This is apparent from the allelic structure. There is a single sweeping variant for SLC24A5: if paleness was the point, many partial loss-of-function alleles would be favored, rather like what we see with G6PD deficiency (a malaria defense). But there is only one: so loss of function is not the point (or at least not the sole point): that particular variant has some other advantage, a big one.”

This looks to me like classic a priori reasoning. Cochran is thinking like a physicist: that is, that because evolution has acted once in a certain way to find a “solution”, it must be expected to act like that in another situation. But that is not how biology works. It is a science with a lot of exceptions and few rules.

And here is what I wrote on physicists and mathematicians attacking biologists for not knowing more mathematics.

4 responses to this post.

  1. Posted by Julian O'Dea on September 13, 2015 at 4:21 am

    Quite interesting and mentions Cochran and germ theory:


  2. Posted by Julian O'Dea on May 7, 2016 at 12:01 am

    On the other hand, biological systems have supposedly inspired human invention. So in that sense biology or evolution can be an optimising process:


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