Tuatara: Volume 26,Issue 2, November 1983
Population Genetics and Evolutionary Theory
Population Genetics and Evolutionary Theory
Population genetics is, by modern standards, a fairly venerable discipline. Its first manifestation seems to have been the formulation of the Hardy-Weinberg Law in 1908, which led a discerning student to christen Wilhelm Weinberg “the father of population genetices.” Since that time the discipline has flourished and fame has descended on such practitioners as Fisher, Wright, Haldane and Dobzhansky.
Population geneticists purport to deal with evolutionary problems, and one of their leading journals is entitled Evolution. The Synthetic Theory of evolution, which has been the ruling orthodoxy from the last fifty years, is a synthesis of several disciplines, but none of the other components have been given as much weight as population genetics. Therefore modern textbooks on evolution devote a good deal of space to this subject. For example, Stansfield (1977) makes population genetics a constantly recurring theme and reproduces portraits of Fisher, Wright, Haldane and Dobzhansky.
It is impossible to say just how much attention is paid to population genetics in the actual teaching of courses in evolution, since this must vary widely with the length of the course and the predilections of the teacher. But without fear of contradiction we can state that it is not easy to teach population genetics. Calculus is often a prerequisite; and most of the journal articles concern such small and technical problems that few students develop a burning interest in the subject.
In view of this situation, many teachers may be relieved or even pleased to learn that it may no longer be necessary to include population genetics in courses on evolution. The reason for this is startling, but can easily be documented, it is simply that the leading workers in this field have confessed, more or less reluctantly, that population genetics contributes very little to evolutionary theory. We will cite three such leaders.
Professor Lewontin of Harvard, in his recent treatise (1974), makes a number of vigorous statements on this point:
(a) It is an irony of evolutionary genetics that, although it is a fusion of Mendelism and Darwinism, it has made no direct contribution to what Darwin obviously saw as the fundamental problem: the origin of species. (page 159)
(b) We know virtually nothing about the genetic changes that occur in species formation. (page 159, in italics).
(c) If one simply cannot measure the state variables or the parameters with which the theory is constructed, or if their measure is so laden with error that no discrimination between alternative hypotheses is possible, the theory becomes a vacuous exercise in formal logic that has no point of contact with the contingent world. The theory explains nothing because it explains everything. It is my contention that a good deal of the structure of evolutionary genetics comes perilously close to being of this sort. (pages 11-12)
(d) How can such a rich theoretical structure as population genetics fail so completely to cope with the body of fact? are we simply missing some critical revolutionary insight…? Or is the problem more pervading, more deeply built into the essence of our science? I believe it is the latter. (page 267)
Professor Spiess of the University of Illinois, in his more recent treatise, (1977) echoes with approval our second quotation from Lewontin and then goes on to say: “Speciation is one of the most critical processes in nature, but we are a long way from describing the origin of species in the field or with methods of experimental population genetics."page 72
Professor Roughgarden of Stanford, in his more recent treatise, (1979) also betrays disappointment with the achievements of population genetics:
We sometimes distinguish population genetics from evolution by the fact that population genetics is often more concerned with a detailed description of the genetic structure of a population and with changes over a shorter time scale than is evolution. Phenomena over long time scales include the radiation of groups of organisms, as exemplified by the radiation of lungfish. We want to understand phenomena of this sort.
Why has the radiation been as extensive as it has been? Could certain forces have caused it to be more or less extensive; what controls the rate at which the radiation occurs; and is there any causal connection between the radiation patterns in different groups? These are all important and fundamental questions, yet we cannot answer them very well. When research into population genetics was begun, it was assumed that these kinds of long-term evolutionary phenomena would be explained as a result. We need to reassess the relevance of popultion genetics to these kinds of evolutionary issues.
In a further effort to verify our suspicions, we dug out four reviews of the Lewontin treatise. All of these appeared in scholarly journals and were written by reputable scientists. Not one of the reviewers took issue with Lewontin's statements, although such disparaging remarks could hardly have escaped their attention.
We would have expected any devoted population geneticist to be grieved by the failures of his profession, but Lewontin was able to be humorous on the subject. Here is his description of the situation:
For many years population genetics was an immensely rich and powerful theory with virtually no suitable facts on which to operate. It was like a complex and exquisite machine, designed to process a raw material that no one had succeeded in mining. Occasionally some unusually clever or lucky prospector would come upon a natural outcrop of high-grade ore, and part of the machinery would be started up to prove to its backers that it really would work. But for the most part the machine was left to the engineers, forever tinkering, forever making improvements, in anticipation of the day when it would be called upon to carry out full production.
Quite suddenly the situation has changed. The mother-lode has been tapped and facts in profusion have been poured into the hoppers of the theory machine. And from the other side has issued nothing. It is not that the machinery does not work, for a great clashing of gears is clearly audible, if not deafening, but it somehow cannot transform into a finished product the great volume of raw material that has been provided. The entire relationship between the theory and the facts needs to be reconsidered. (page 189)
If the leading authorities on population genetics confess to this dismal lack of achievement and even chuckle about it, it is altogether fitting and proper for the rank and file to take them at their word. Therefore it seems to follow that there is no need to teach population genetics in introductory courses on evolution, although advanced courses may include it as a matter of history.
Clarke, B. 1974. Review. Science 186: 524-525.
Lewontin, R. C. 1974. The Genetic Basis of Evoutionary Change. Columbia University Press, New York.
Robertson, A. 1975. Review. Nature 254:367.
Roughgarden, J. 1979. Theory of Population Genetics and Evolutionary Ecology. Macmillan, New York.
Spiess, E. B. 1975. Review. Paleobiology 1:131-135.
—— 1977. Genes in Populations. John Wiley and Sons, New York.
Stansfield, W. D. 1977. The Science of Evolution. Macmillan, New York.
Strauss, B. S. 1974. Review. American Society of Microbiology News 40:956-958.