How did Darwin come up with his ideas?
"The Origin" was concerned with Pattern and Process
3. Objections to Darwin's Theory
Philosophical and theological objections to the theory
Philosophical views concerning "Origin of Species" over
the ages
For 2000 years, the organization of the biological world followed classical Greek ideas derived from Plato and Aristotle.
To Aristotle, the species on earth were typified by an "idea" or form that exists in a transcendental world. eidoz is translated as species.
Theologians took this philosophy and created from it an order to the
biological world, the Scala Naturae, great chain of being that God had created.
There was also design and purpose to every rung in this Ladder of being or the Systemae naturae.
If everything had purpose and there was an initial design, how could species go extinct?
Moreover, there was no room for modification and speciation, the rungs of the ladder really formed a gradation with no gaps.
Evolution -- literally means an unfolding, and participants in the
development of the concepts
"when the ideas of species are generally admitted, we can dimly foresee that there will be a considerable revolution in natural history."
This shift in thinking from the typological to individuals
was the profound shift in conceptual insight (combined Malthus & Lyell).
Darwin returns from the voyage of the Beagle and a fellow ornithologist
points out the variation in mockingbirds (not in Darwin's Finches as is
commonly believed).
Why didn't he publicly announce it until 1858 and only then because
he had received a communication from Alfred Russell Wallace?
A partial answer was Darwin's inner turmoil that is captured in a letter
to Sir Joseph Hooker on the immutability of species:
"I am almost convinced, (quite contrary to the opinion I started with) that species are not (it is like confessing a murder) immutable." This was to murder Lyells ideas concerning the immutability of species.
Darwin and Wallace conceived of ns. Both delivered address
to the Linnean Society in 1858.
Darwin published the big book On the Origin of Species --1859 (11-24).
PATTERN: Most scientist accepted the idea of evolution within
~20 years.
PROCESS: The notion that it is natural selection on individual
variation leads to evolution -- an argument over PROCESS -- was not readily
accepted largely because of typological thinking. What was required was
a change to population thinking and variation of type. And then there were
also fundamental arguments over the mechanisms of inheritance.
What was revolutionary about Darwin's thinking:
The theory also was a dramatic departure from typological thinking.
Typological thinking -- Explain previous work in the context of
unity of type. Versus the study of Variation among individuals per se.
Why wasn't the theory accepted immediately?
C. Darwin (1859) On the Origin of Species
Again, it may be asked, how is it that varieties, which I have called incipient species, become ultimately converted into good and distinct species ...?
All these results, ..., follow from the struggle for life. Owing to this struggle, variations, however, slight and from whatever cause proceeding, if they be in any degree profitable to the individuals of a species, in their infinitely complex relations to other organic beings and to their physical conditions of life, will tend to the preservation of such individuals, and will generally be inherited by the offspring. The offspring, also, will thus have a better chance of surviving, for, of the many individuals of a species which are periodically born, but a small number survive. I have called this principle, by which each slight variation, if useful, is preserved, by the natural selection ...
The formulation of the theory of natural selection is an example of what is called a "syllogism". A syllogism may be defined as "a form of reasoning in which a conclusion is drawn from several given or assumed premises". What this means is that the concept of natural selection results as an inevitable outcome of the acceptance of certain biological facts. What are these facts and what is their origin?
Fact 1. Natural populations have enormous excess fecundity.
Source: Paley, Malthus.
Fact 2. Population sizes remain stable.
Source: wide acceptance for 100's of years.
Fact 3. Limitation of resources.
Source: wide acceptance in early 19th century.
Inference 1. A severe struggle for existence must occur.
Source: Malthus.
Fact 4. An abundance of variation exists among individuals of a species.
Source: animal/plant breeders, taxonomists.
Fact 5. A proportion of this variation is heritable.
Source: animal/plant breeders.
Inference 2. There must be a non-random survival of individuals resulting, in part, from genetic differences.
Author of inference: Darwin.
Inference 3. Over many generations evolutionary change must occur in the population.
Author of inference: Darwin.
In essence, Darwin took what Malthus had argued and showed how that once
you include variation and inheritance into the equation, natural selection
and biological evolution are inevitable consequences.
Heritability -- If only Darwin had cracked open the copy of Mendel.
Darwin's views of heredity left him open to attack by his critics. Darwin even backpedaled in later editions of the origin, and reverted to neo-Lamarckian views of inheritance to maintain variation in the face of natural selection (see below).
Evolution has no direction, no progress, ns is a purely blind and mechanical
PROCESS. The relentless elimination of less fit variants ran against
the notion of a design in nature. These philosophical objections
are wonderfully summarized by John Dewey (1909) a contemporary philosopher:
"The Darwinian principle of natural selection cut straight under this philosophy [that of design]. If all organic adaptations are due simply to constant variation and the elimination of those variations which are harmful in the struggle for existence that is brought about by excessive reproduction, there is no call for a prior intelligent causal force to plan and preordain them. Hostile critics charged Darwin with materialism and with making chance the cause of the universe."
Specific Scientific Objections:
1) Do a diagram of blending inheritance on the blackboard -- Fleming
Jenkins [This will be extended to Galton and the phenomenon of regression
in lectures on heritability]
2) All neo-Lamarckian views (e.g., Darwin's and others) were rejected
by August Weismann -- rejects influence of soma on the germ plasm
3) Galton comes to the conclusion that evolution arises
from sports -- discontinuous evolution is the dominant mode, not gradual
change as Darwin espouses. Huxley says the arise from "sports"
and also challenged Darwin. Both Galton and Huxley were staunch supporters
of Evolution but they disagreed on this aspect of inheritance.
Alternative processes to
explain Evolution
Battle of the 1890's and early 1900's -- Battle of the Biometricians
and Mendelians
Weldon & Pearson vs Bateson & Hugo deVries
and mutationstheorie
Bateson and deVries (mendelian traits and mutationstheorie) -- evolution
proceeds by discrete jumps (mutations) [Huxley and Galton, two of Darwin's
supporters believed this theory] not via gradual change (Weldon, Pearson]
IF EVOLUTION OF SPECIES OCCURS BY SALTATIONS OR LARGE DISCONTINUOUS
JUMPS (THE MECHANISMS OF INHERITANCE), HOW CAN THE GRADUAL FORCE OF NATURAL
SELECTION POSSIBLY BE RELEVANT?
Reaches an all time low in the 1920's with attacks from: