Reply #133: We have fossils, we win!

[ozone_man]

Evolution does have extraordinary evidence. The Theory of Evolution is more than a theory. It's fact. regarding the gradual change that you mention, gradual is a relative term, a thousand generations is gradual, but may look abrupt in the fossil record. He's saying that this change won't occur in one generation (see below).

In both scholarly and popular literature one frequently finds references to "Darwin's theory of evolution", as though it were a unitary entity. In reality, Darwin's "theory" of evolution was a whole bundle of theories, and it is impossible to discuss Darwin's evolutionary thought constructively if one does not distinguish its various components.

... The term "Darwinism", ... has numerous meanings depending on who has used the term and at what period. A better understanding of the meaning of this term is only one reason to call attention to the composite nature of Darwin's evolutionary thought.

... One particulary cogent reason why Darwinism cannot be a single monolithic theory is that organic evolution consists of two essentially independent processes, as we have seen: transformation in time, and diversification in ecological and geographical space. The two processes require a minimum of two entirely independent and very different theories.

... I consider it necessary to dissect Darwin's conceptual framework of evolution into a number of major theories that formed the basis of his evolutionary thinking. For the sake of convenience, I have partitioned Darwin's evolutionary paradigm into five theories, but of course others might prefer a different division. The selected theories are by no means all of Darwin's evolutionary theories; others were, for instance, sexual selection, pangenesis, effect of use and disuse, and character divergence. However when later authors referred to Darwin's theory thay invariably had a combination of some of the following five theories in mind:

- Evolution as such. This is the theory that the world is not constant or recently created nor perpetually cycling, but rather is steadily changing, and that organisms are transformed in time.
- Common descent. This is the theory that every group of organisms descended from a common ancestor, and that all groups of organisms, including animals, plants, and microorganisms, ultimately go back to a single origin of life on earth.
- Multiplication of species. This theory explains the origin of the enormous organic diversity. It postulates that species multiply, either by splitting into daughter species or by "budding", that is, by the establishment of geographically isloated founder populations that evolve into new species.
- Gradualism. According to this theory, evolutionary change takes place through the gradual change of populations and not by the sudden (saltational) production of new individuals that represent a new type.
- Natural selection. According to this theory, evolutionary change comes about throught the abundant production of genetic variation in every generation. The relatively few individuals who survive, owing to a particularly well-adapted combination of inheritable characters, give rise to the next generation.
Let's look at some of the implications of Mayr's analysis.

At first blush, (4) Gradualism seems like it might conflict with Gould & Eldredge's "punctuated equilibrium" theory; but on closer examination, not so.

Here are two relevant quotes from On the Origin of Species:


"... it is probable that the periods, during which each underwent modification, though many and long as measured by years, have been short in comparison with the periods during which each remained in an unchanged condition." (from the final 6th edition, 1872)

"Varieties are often at first local...rendering the discovery of intermediate links less likely. Local varieties will not spread into other and distant regions until they are considerably modified and improved; and when they do spread, if discovered in a geological formation, they will appear as if suddenly created there, and will simply be classed as new species."

Darwin did not claim that evolutionary change is slow and continuous -- only that it does not proceed by "jumps" in a single generation (what Mayr calls "saltational" change). That is, despite the distortions of some anti-evolutionists, Darwin explictly did not think that evolution proceeds by the production of "hopeful monsters" -- Darwin himself never proposed that a fully-dinosaur parent gave birth to fully-bird progeny. Rather, the change took place in a series of intermediate, perhaps nearly insensible, steps in successive generations. Note that change over a thousand generations of any species appears as "sudden" or "abrupt" change in the fossil record, because a thousand generations is such an infinitesimally small fraction of Earth's history.

http://www.talkorigins.org/faqs/darwinism.html