The charge that the construction of the geologic scale involves circularity has a certain amount of validity. ...Thus, the procedure is far from ideal and the geologic ranges are constantly being revised (usually extended) as new occurrences are found.

There are millions of different species of animals and plants on earth--possibly as many as forty million. But somewhere between five and fifty BILLION species have existed at one time or another. Thus, only about one in a thousand species is still alive--a truly lousy survival record: 99.9 percent failure!

Now let me step back from the problem and very generally discuss natural selection and what we know about it. I think it is safe to say that we know for sure that natural selection, as a process, does work. There is a mountain of experimental and observational evidence, much of it predating genetics, which shows that natural selection as a biological process works.

Perhaps the only thing that saves science from invalid conventional wisdom that becomes effectively permanent is the presence of mavericks in every generation - people who keep challenging convention and thinking up new ideas for the sheer hell of it or from an innate contrariness.

A new theory is guilty until proven innocent, and the pre-existing theory innocent until proven guilty ... Continental drift was guilty until proven innocent.

It has been argued that dinosaurs did not die out, but just evolved wings and flew away. At a certain level, this reasoning is sound.... Birds, as a group, did descend from dinosaurs and ... all 8,600 species of birds living today carry some inheritance from their reptilian ancestors.

We now have a quarter of a million fossil species, but the situation hasn't changed much... We have even fewer examples of evolutionary transition than we had in Darwin's time.