Path: utzoo!attcan!uunet!lll-winken!ames!ncar!tank!ogil
From: ogil@tank.uchicago.edu (Brian W. Ogilvie)
Newsgroups: sci.bio
Subject: Re: Creationism in our schools and the Anti-Dogma statement
Summary: Darwin IS current
Keywords: Darwin Eldredge Gould saltation
Message-ID: <1398@tank.uchicago.edu>
Date: 12 Jan 89 22:49:17 GMT
References: <8558@pasteur.Berkeley.EDU> <2630002@hpcilzb.HP.COM> <13338@cup.portal.com> <206@maths.tcd.ie> <209@maths.tcd.ie>
Reply-To: ogil@tank.uchicago.edu (Brian W. Ogilvie)
Organization: History of Science, University of Chicago
Lines: 69

In article <209@maths.tcd.ie> mlloyd@maths.tcd.ie (Michael Lloyd) writes:

>First, I wouldn`t try talking about Darwinism too much - the views of
>Darwin himself are hardly still current.  His continuum of evolution
>has little experimental support - the records are a little too `broken`
>for that.  I believe (any corrections, folks?) that the field now runs
>at three main theories for a mechanism of evolution.  So try talking
>about Evolution in general rather than the views of Darwin.
>
>Mike 

As a historian of evolution I must take issue with this statement. Darwinism
may be divided into three essential components:

1. Theory of Variation. Organisms vary in their characters. These variations
are quite small. We don't know what causes them.

2. Theory of Inheritance. Offspring tend to resemble their parents. Characters
of offspring are intermediate between the characters of their parents, plus
any variation which might occur (from unknown causes of point 1).

3. Theory of Natural Selection. Organisms are superfecund--more are born
than can possibly survive. Hence those possessing VARIATIONS which make them
more likely to survive (even minutely) than their fellows will tend to live
longer and produce more offspring, and if those variations are HERITABLE the
offspring will possess that character. Since these offspring will be more
common than their parents, the distribution of traits in the population will
shift. The process is slow but inexorable, given that the same trait is always
advantageous.

Mendelian heredity has confirmed the first point; while it permits large
"saltational" variation, William Castle demonstrated in the 1910's that it
also permitted apparently continuous variation through the interaction of
a number of genes. While Darwin's "Provisional Hypothesis of Pangenesis" for
inheritance has been discredited, Mendelism has provided a theory of
heredity that is not too different (although it does not allow for the
"Lamarckian" inheritance of acquired characteristics that Darwin thought
possible). Current debate ranges around the INTERPRETATION of Natural
Selection.

Niles Eldredge and Stephen Jay Gould proposed in 1972 their theory of 
"punctuated equilibrium," which holds that species remain relatively
stable for most of their existence and that species change occurs rather
quickly (in a geological sense) among small populations. They made this
proposal in order to account for the absense of transitional varieties in
the fossil record, a fact which Darwin explained by the relative infrequency
of the sedimentation processes which preserve fossils. They still believe
that natural selection acts between these new species and their ancestors,
but the process of speciation, due to the small population sizes involved,
is governed predominantly by nonadaptive, stochastic processes.

The current orthodoxy is perhaps best represented by two men: Ernst Mayr
and the late Sewall Wright. Mayr, an ornithologist, is responsible for the
theory of allopatric speciation, which holds that speciation occurs in
peripheraly isolated populations (like Gould and Eldredge) but that selection
plays a major role in the process. Wright, who was a theoretical population
geneticist, had a similar theory where random drift played an important but
by no means exclusive role in speciation.

To sum up, the broad outlines of Darwinism are still present in modern
evolutionary theory, although the details have changed and his emphasis on
selection as the major force at work has shifted somewhat. In fact, modern
evolutionary theory (since the 1940's) is more Darwinian than that
immediately following Darwin, which can be characterized broadly as 
"neo-Lamarckian" or "orthogenetic." Darwinism is still a valid description
of evolutionary thought.

---
Brian W. Ogilvie   /   ogil@tank.uchicago.edu