crownboy

How have scientist been able to determine that such a high % are now gone? I don't think there are enough fossils to make this determination, so how did they get to that number? Do they make extrapolations based on the number of exstinctions that have been recorded in our time and used it to determine how it was back then, or are there other methods?



[ October 03, 2002: Message edited by: crownboy ]</p>

Coragyps

Crownboy, I'm moving this thread to Evolution/Creation, as I think you'll get livelier response there.

Nat

I think they base it on observed species in the fossil record - find a hadrosaur fossil, can't find a living hadrosaur, the hadrosaur must then be extinct.

Valentine Pontifex

Actually the number of species observed in the fossil record is far smaller than what is observed today. Of course most species that live today don't fossilize very well.

Duvenoy

When one compares the number of species alive today, plant and bacterial as well as animal, to the number of species that have disappeared over the last 3.5 billion years, I think that the 99% estimate might be a trifle low.

Evolution plays a great part in the extinction of species. A species will evolve into others, scarcly resembling the original (which evolved from something else). And that original species might or might not 'die out'. Many of it's decendents won't compete due to changing, natural pressures, and they will die out. And then come the great extinctions when a great deal of the larger life on the planet was wiped out. The end of the dinosaurs, some 65 million years ago, as an example. It brings up the thought of how many smaller species, down to bacteria and so forth, and plants also perished with the great reptiles.

It will never be known exactly how many species have existed upon the earth, but those alive today are but the most minute fraction of those that have preceeded them (us).

doov

Vampyric

Sorry to hijack the thread, but I just wanted to ask; does a species become extinct if it evolves into another?

I know it seems simple, but extinct suggests it died out rather than moved on (at least to me), so coudl you please include how you define extinct in your response?

Camaban

The way I see it is this:

If there are no members of a species left, that species is extinct.

IE, Dinosaurs evolved into birds, yet dinosaurs (Yes, I know there are exceptions) are by and large, extinct.

If it evolves into a new species, the old species is still extinct.

Thor Q. Mada

It is statistics, and as Mark Twain said (in more rough terms), with figures you can do what you want.
For example: 99% of all the nuclear physisists that ever lived on this earth, still live today. Useless and meaningless but probably true.
Or smoking increases the chances of female breast cancer by 60%. A casual reader might think that the chances are 60%, but it is the increase on the small chance that is 60%.
Or our business figures went up by 100%. Big deal if you didn't sell anything the previous year, but it helps stock values to go up.
Never trust figures in the newspapers. Never trust statistics without looking at how they were derived, how the sample looked like, and how the boundary conditions used were.

Gregg

No, not necessarily.

If the population of a particular species is widespread, you might have evolutionary change occur only in an isolated population of the species that's subjected to unique environmental pressures. The bulk of the population, still well-suited to its "niche" continues on relatively unchanged, while in the isolated population, the descendants of better-adapted individuals eventually out-compete and overwhelm those that aren't as well-adapted. This can happen pretty quickly--try reading "The Beak of the Finch."

Or consider polar bears. Let's assume they evolved from black bears. Well, black bears obviously haven't died out. But for bears in regions perpetually covered with snow, having lighter fur as camoflauge probably increased the chances of a successful hunt. So white-furred bears eventually displaced dark-furred bears in those regions.

Of course, these are examples of adaptation within a species, not speciation. But there's no reason to think that an isolated population of a species, subjected to different environmenal pressures, couldn't evolve into something very different from the original population, while those descendants from the original population who continue living under basically the same conditions as their ancestors remain relatively unchanged.

Gregg

Oolon Colluphid

The book to get hold of is David Raup’s Extinction: Bad Genes or Bad Luck?. Haven’t had time to read it myself yet, but it apparently covers all this.

Cheers, Oolon

[Edited to correct the typo 'Bad Genees' before Boro Nut sees it ]

[ October 04, 2002: Message edited by: Oolon Colluphid ]</p>

Fixed link- J.