A question for the biologists . . . Received wisdom goes something like this: Circa 1860 Darwin had just proposed his theory of natural selection to an unsuspecting world. But the big honchos of the day (Lord Kelvin et al) put a damper on the proceedings by insisting that the Earth is only 20 million years old or something. Everyone shrugged and said "Darwin, you're fooked. Twenty millions years isn't nearly enough time for natural selection to produce the biological diversity we see before us. Go stand in the corner". Then we found out the Earth was a lot older, all was well, and Darwin smiled for the first time in his life. My question is: How exactly did they determine that twenty million years isn't enough? A lot can happen in twenty million years.