January 1, 2012
To be posted on nobabies.net
Kevin N. Layland
School of Biology
University of St. Andrews
KY169TS
UK
knl1@st-andrews.ac.uk
Dear Kevin Layland:
I read your engaging, not to say strenuous, article. (Kevin N. Layland et al. Cause and Effect in Biology Revisited: Is Mayr’s Proximate-Ultimate Dichotomy Still Useful? SCIENCE vol. 334 no. 6062 December 16, 2011 page 1512) You recall that Ernst Mayr fifty years ago declared that one must distinguish between ultimate causes (Why do birds migrate? This is an evolutionary issue) and proximate causes (How do birds migrate? This is an issue of the molecular biology of the birds). You point out convincingly that things are more subtle and complex.
My friends and I had a joke forty eight years ago: The bum is different because he is lying in the gutter, and the gutter is different because the bum is lying in it. More seriously you point out that the soil has certain properties because it has been worked by earthworms and the earthworms then had the opportunity of evolving to exploit better the new properties. You go on with several examples and a scheme that leaves the simplistic analysis wanting.
I was particularly taken with your remark about how conceptual frameworks channel thinking and hinder paradigm shift. On the assumption that you have warm fuzzy feelings for paradigm shifts, let me offer you one.
Consider a valley with animals, let’s say mice, isolated from other valleys. A glacier forms dividing the valley and separating the mice into two viable and similar but distinct populations. After two thousand mouse generations the glacier melts and the populations have access to each other. But they cannot have fertile offspring because over the years speciation has occurred.
Now consider the same valley. There is one mouse with a particular chromosome that it passes to two offspring. This time there is no glacier. But there is a population of a thousand and they mate at random. Since each mouse has two chromosomes of this sort it will take on average two thousand generations for those two chromosomes to meet again, by which time they can no longer do business together. Since this is true for every chromosome and every part of every chromosome, the population must die out.
That is the nutshell. With this much I have annoyed my family, alienated my friends and been a nuisance. A couple of days ago following such logic I drove two bright young men into hysterics. I assume that by contrast you are still here.
The logic is iron clad given three things. There must be Mendelian inheritance. That is a certainty. There must be reasonably prompt speciation. That takes a little hand waving; Darwin said speciation is happenstance because hybrid infertility never did any species any good. But that obviously is not true. Speciation is needed for the evolution of diverse complex organisms. So it is a certainty. The third leg of course is the random mating in a large population which in real life almost never happens, at least not for long.
So given this existential threat to any species nature had to come up with some way to prevent random mating. Aha, you say. Now the whole point of migration is clear. The birds (or fish or whatever) are not migrating to find food; that is just an exploitable opportunity. The real point is going right back to the home roost (or brook or patch of ice covered ground) to find what cannot be found anywhere else on earth: kissing cousins.
One geneticist I pointed this out to dismissed it saying, “But you don’t have a mechanism.” So I worked for ten years or so and now can say the mechanism is epigenetic, may be pre-zygotic (probably never in isolation) post-zygotic or a combination and can be modeled with a computer program.
So I had the ultimate cause fairly early on and evidence to support it. The proximate cause has been a bigger challenge.
But the biggest challenge of all is of course that this is a paradigm shift. Everybody loves Darwin for whom evolution is all about maximizing fertile offspring. And everybody loves Malthus, at least the part where he says that environment permitting any life form will multiply without limit.
I have put evidence on my web site nobabies.net. The Orlando summary is my most recent.
Any ideas about how to encourage a paradigm shift? Let me know what you are thinking.
Sincerely,
M. Linton Herbert
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