Let's take it from the top.
(1)
Evolution is a heritable change in the composition of a gene pool.
This would include a lot of things. The changes in the beaks of the finches is evolution. The descent of humans from what we may as well call "monkeys" would be evolution. If every lioness in the world stopped giving birth to lion cubs and started giving birth to unicorns, and this involved a change from lion DNA to unicorn DNA (and how could it not?) then this would also be evolution. Indeed, if all lions suddenly
turned into unicorns, by magic or the will of God, and this change was inherited by their offspring, then this too would be evolution.
(2a) The principle of
common descent is the proposition that all present species have been produced from just one original life-form by evolution.
(2b) A claim of
common ancestry concerning any bunch of species is the claim that they all evolved from the same species. So common descent is the claim that all species have common ancestry.
(3) The
theory of evolution is a theory about
how evolution happens. It proposes that it occurs as a result of such well-known genetic processes as reproduction, mutation, recombination, lateral gene transfer, natural selection (including sexual selection), artificial selection, genetic drift, and the laws of probability.
Note that this theory is a
constraint on evolution (just as every other scientific theory is a constraint on its subject matter). It says what
can't happen --- for example, it rules out lions giving birth to unicorns.
The principle of common descent is almost always taken to be the initial condition for the theory of evolution, so much so that people often speak of it as part of that theory. I've done that myself, I admit. But to be accurate we should separate them, just as the proposition that the Universe began with a Big Bang is separate from Einstein's theory of General Relativity.
(4) The law of
natural selection is the proposition that those organisms which are genetically best suited to propagate their genes will indeed tend to get their genes propagated better than those organisms that are less well-suited to that task.
---
Now, let's look at what creationists should be saying.
You shouldn't say: "I don't believe in evolution", 'cos it happens.
You shouldn't say: "I don't believe in the theory of evolution" unless that's absolutely what you mean. Because a lot of creationists do believe in it, and believe that they can use it to
disprove common descent. My favorite creationist slevesque is going down that route. Remember that, as I said, the theory of evolution places
constraints on what evolution can do. If anyone wants to prove that common descent couldn't possibly happen, then the theory of evolution is the only tool they've got to work with.
You shouldn't say: "I don't believe in natural selection", because the law of natural selection is so obvious that you could prove it from your armchair without even glancing at nature.
What you
should be saying is: "Yes,
evolution happens, we observe it. And I grant you, indeed I
insist, that there are no known mechanisms for evolution except those enumerated in the
theory of evolution. And in particular the law of
natural selection is so obvious that no sane person could dispute it. What I dispute is the
common ancestry of men and monkeys and indeed the whole principle of
common descent".
And if you were someone who argues after the style of slevesque, you should then add: "As a matter of fact, I think that the
theory of evolution puts the tin lid on the whole notion of
common descent".
Edited by Dr Adequate, : No reason given.
™ Version 4.2
