A Brief History of Evolutionary Genetics

 being some account of:

the major questions in the science of inheritance
as it relates to evolutionary phenomena,
the ideas proposed as answers,
those who developed these ideas,
where the ideas came from,
and how the whole thing moved forward
from Darwin's day to the present.

by Paul Handford

Department of Zoology
University of Western Ontario


This history has been compiled from a diversity of sources, which are provided in a General Bibliography  Other reference materials are provided in footnotes scattered throughout the text.

For convenience of downloading, this document has been separated into several parts, as indicated in the list of links at the bottom of this page.

A preamble to this history follows immediately below.


Preamble

We have long sought to understand inheritance

Inheritance has always fascinated us, for it has always been of supreme importance.  Since becoming self-conscious pastoralists and farmers, beginning about 10 thousand years ago, we have been occupied in altering the nature of our domestic stocks, and, at least since the development of complex societies, we have been concerned to explain our own character diversity.  Thus, long before science was developed as a coherent and rational system for investigating natural phenomena, we have constructed explanations for the character variation of new generations of organisms, whether of our livestock, our crop-plants, or of ourselves.

From earliest times, we have been aware of different sources of influence in character inheritance.  First, the idea of "blood" - that "like begets like" - that the nature of a new generation somehow involves the intrinsic character of the parents.  Second, we have recognised that external conditions can profoundly influence outcomes - for example, good growing conditions in crop plants, diet quality in livestock, and human material or cultural resources (that other form of "inheritance") were all recognised as important sources of influence (albeit to varying degrees) on the "character-outcome" of breeding events, and thus on the variation among individuals.

Culture & society influence the practice of science

It is important to recognise, and to keep in mind as we proceed, that many issues in genetics have thus long held central importance in the human sphere, and it should be no surprise, therefore, that many deeply-seated attitudes and assumptions have often been involved in our assessment of the relative importance of these different sources of causation in our explanations of character variation.  The suggestion that cultural attitudes (which are, by definition, outside of science) may yet have an impact on the development and (at least the initial) evaluation of scientific ideas may be surprising, but this is a well-established dynamic, widely recognised by historians and philosophers of science, if not always by scientists themselves, and this seems to be true, to some extent at least, in most, if not all, branches of science.  We must thus be ever-watchful for unjustified (not necessarily unjustifiable)  assumptions which may creep into our thinking and unconsciously provide non-scientific bases for our ideas, and/or our choices among them.  We will meet several examples of just this sort of thing as we go along.  What is distinctive and reassuring about science is that such assumptions sooner or later get exposed as assumptions, and their ramifying consequences identified.  Sometimes it is necessary to make radical reappraisals of our 'knowledge' following such events.  We will meet examples of this, too.

Science builds models to represent reality;  but models always remain models

One must also recognise another important element in the nature and conduct of any science.  Science proceeds by the construction of intellectual models about the structure and functioning of the natural world, followed by the evaluation of these models, by testing their implications through observation and measurement.  Models thus account for current findings (they 'explain' them), and then extend beyond them into the as-yet unknown, but observable, world.  Sometimes these models (usually called hypotheses) quickly fail these tests, and don't live very long in the scientific imagination as a good reflection of "reality."  But sometimes, they repeatedly pass ever more diverse tests and, in so doing, become more complex and broad in their explanatory scope.  They thus develop, as we usually say, into "theories", which provide us with greater confidence that we are on to something real in our understanding of the structure of some part of the cosmos — that the pictures they provide aren't distorted.  A fine example of such a theory is that of evolutionary descent and diversification of life:  the idea that it happened provides a coherent explanation of an enormous array of diverse information (it's the only one we have that does so), even though we are still working on many details of exactly what happened and exactly how it works. 

But before a set of ideas becomes a robust and complex theory, like evolutionary theory, it is in a rather grey region, wherein it is only as yet provisionally successful and partially evaluated.  During this phase, it is extremely easy to mistake the model for reality itself, especially if the picture of the world that it offers chimes pleasantly with cultural notions from outside of science.  It is here that the influence of the attitudes and assumptions mentioned above can creep in and colour our scientific judgment.  To the extent that they do exert such influences, these judgments cease to be strictly scientific, and tend towards guesswork and prejudice.  Even the most thoroughly-tested models always remain models, although we may have great confidence in them as providing a realiably accurate picture of how things work.  A cautionary example is provided by Newtonian mechanics, which almost everyone in science regarded AS the real world for over two hundred years;  Einstein showed us that it was only a partially clear reflection of the "real" world - true in its domain, but a limited picture nonetheless. 

So, in our consideration of evolutionary population genetics, keep firmly in mind that we are, much of the time, describing models of the world of inheritance across generations, models of the nature and distribution of variation within and among populations, and so on.  These models may get extended far beyond the firm empirical base of the time.  Even the scientists involved sometimes forget where the boundary between assumptions and established fact lies.......

Science is about reducing our uncertainty about the structure of the natural world;  much uncertainty remains about many basic matters in evolutionary genetics

As a final reflection before beginning our outline of the development of ideas in the evolutionary genetics of populations, you should be prepared to discover great uncertainty of understanding:  not about the theory itself, but about the empirical facts of the matter, to which the theory is designed to correspond.  The developing theory has helped enormously in defining critical areas for empirical research and refining the particular questions posed of nature, but the resultant empirical base is still enormously patchy, still far from adequate for making any definitive, global, choices between the major rival theoretical models of the structure of the populations themselves and of their major evolutionary patterns and processes.  

What is the primary driver of evolution within populations?  is it selection?  or chance?  What dictates the differentiation among conspecific populations?  is it chance?  or selection?  What drives the formation of new species?  is it selection?  or chance?  Whether chance or selection, or some mix of the two, be the answers to these questions, how is the evolutionary future of any given population or group influenced by its unique history? - can some evolutionary futures simply be unreachable given certain evolutionary pasts?  - can evolution be the kind of process where, so to speak, "you can't get there from here?"  In short, is evolution, at any level, from the individual up through species to the higher taxonomic categories, primarily adaptive or primarily influenced by chance?  and how is it constrained by history?  Is there any necessary connection between the correct answer to any one of these questions and the correct answer to any of the others?  Are there any globally-true answers at all, or is nature just local and contingent:  sometimes the answer is A, sometimes B?  We know some answers to some questions of this sort in some rather small number of real cases, but global answers are not yet forthcoming.  Some say we will never really be sure which is the best answer.

As you study this history, you should gain an appreciation of what, exactly, are the important questions in evolutionary population genetics, why they are important and what theory tells us of possible answers.  Just as theoretical population genetics itself largely rests on a rather small and rather insecure factual base, so does the teaching of population genetics all too often rest on an insecure appreciation of what the real questions are in the first place.

  


Links to the other sections of this history

Early Days

Mendelism & Darwinism

Ronald Fisher

Sewall Wright

J.B.S. Haldane

Dobzhansky

The New Synthesis to Now

General Bibliography




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Maintained by: Paul Handford <handford@uwo.ca 

Last update: 2011-08-19