What is Evolution?
(apologies if something like this has been posted)
A review of Darwins Theory (On the Origin of Species by means of Natural Selection)
Evolution: Organisms change through time. Supported by the fossil record, and nature (Darwin's study of bird species in South America and the Galapogos Islands)
Descent with modification: Evolution proceeds via branching through common descent. Offspring are similar but not exact replicas of their parents. This produces the necessary variation to allow for adaption to an ever changing environment.
Gradualism: Change is slow.
Multiplication of speciation: Evolution does not just produce new species. It produces an increasing number of new species.
Natural selection: The mechanism of evolutionary change.
This mechanism - proposed by Darwin and Wallace - operates as follows
1. Populations tend to increase geometrically (2,4,8,16,32, ... etc)indefinitely
2. In a natural environment, population numbers stabilise at a certain level.
3. Therefore, there must be a 'struggle for existence', because not all organisms produced survive
4. There is variation in every species.
5. In the struggle for existence, those individuals with variations that are better suited to the environment leave behind more offspring than individuals that are less well suited. This is known as differential reproductive success.
Point 5 is crucial.
Natural selection has nothing to say about evolutionary direction, species progress, human inevitability, the necessary evolution of intelligence, or God.
There is no evolutionary ladder, with humans at the top, only a
sprouting bush with humans as one twig among millions. There is nothing special about humans; we are good at differential reproductive success.
Darwin published this theory in 1859. No theory stands unchallenged. The most controversial issue today is Gradualism. Gould and Eldredge are pushing for a theory called Punctuated Equilibrium (which involves rapid change then stasis) to replace gradualism.
Note that scientists are not debating whether evolution happens, they are debating the rate and mechanism of evolutionary change.
I will summarise the creationist view and publish a rebuttal in a later post.
w. |
