# Species extinction **URL:** \ **Category:** Factual Questions\ **Created:** [January 13, 2013, 4:46am UTC](https://boards.straightdope.com/t/species-extinction/647035 "2013-01-13T04:46:16Z")\ **Posts on this page:** 11\ **Page:** 1
**Author:** ![scoutdad](https://avatars.discourse-cdn.com/v4/letter/s/ce73a5/32.png) [@scoutdad](https://boards.straightdope.com/u/scoutdad)\ **Post date:** [January 13, 2013, 4:46am UTC](https://boards.straightdope.com/t/species-extinction/647035/1 "2013-01-13T04:46:16Z")
I have read that there are anywhere from 2 million to 100 million nonmicrobial species on this planet, with one supposed best estimate of 8.7 million. I have also read that an estimated 99.9% of species that ever lived are extinct. Surely we don’t have fossil remains of eight billion or so extinct species. So how do we know that such a high percentage of species that ever lived have gone extinct? ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [January 13, 2013, 4:49am UTC](https://boards.straightdope.com/t/species-extinction/647035/2 "2013-01-13T04:49:25Z")
We don’t know-- That’s why they call it an estimate. As to how they come up with that estimate, it’s probably mostly a matter of assuming that the number of species is roughly constant with time, and measuring the rate of evolution of the species we have now to estimate how long ago their ancestors would have been considered a different species. ---
**Author:** ![Peremensoe](https://avatars.discourse-cdn.com/v4/letter/p/ce7236/32.png) [@Peremensoe](https://boards.straightdope.com/u/Peremensoe)\ **Post date:** [January 13, 2013, 5:03am UTC](https://boards.straightdope.com/t/species-extinction/647035/3 "2013-01-13T05:03:32Z")
Most extinct species are likely to be evolutionary branches with no living descendants. Also, the number of species isn’t constant. There have been notable flowerings of diversity, and mass extinctions. ---
**Author:** ![Peremensoe](https://avatars.discourse-cdn.com/v4/letter/p/ce7236/32.png) [@Peremensoe](https://boards.straightdope.com/u/Peremensoe)\ **Post date:** [January 13, 2013, 5:14am UTC](https://boards.straightdope.com/t/species-extinction/647035/4 "2013-01-13T05:14:26Z")
Anyway, talking about species over time is always going to be a somewhat semantic question. Like asking how many generations back was your ancestor who wasn’t in your family. ---
**Author:** ![Darwins\_Finch](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/darwins_finch/32/20304_2.png) [@Darwins\_Finch](https://boards.straightdope.com/u/Darwins_Finch)\ **Post date:** [January 13, 2013, 5:22am UTC](https://boards.straightdope.com/t/species-extinction/647035/5 "2013-01-13T05:22:12Z")
The original estimate appears to have come from David Raup. In his book _Extinction: Bad Genes or Bad Luck?_, he says the following: > [@](#): > > 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! (emphasis in original) So the question then becomes, where did the estimate of 5-50 billion species that have ever existed come from. That estimate appears to come from a combination of the ratio of extant, fossilizable species relative to all extant species (itself an estimate), combined with the average species “lifespan” (cited anywhere from 1 - 10 million years) and estimates of average biodiversity over time. Obviously, these are all very fuzzy numbers, since none of the required values can ever actually be known. ---
**Author:** ![Musicat](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/musicat/32/20189_2.png) [@Musicat](https://boards.straightdope.com/u/Musicat)\ **Post date:** [January 15, 2013, 12:11am UTC](https://boards.straightdope.com/t/species-extinction/647035/6 "2013-01-15T00:11:04Z")
> [@Peremensoe](#): > > Most extinct species are likely to be evolutionary branches with no living descendants. I’d say that’s pretty much the definition of one. ---
**Author:** ![OldGuy](https://avatars.discourse-cdn.com/v4/letter/o/3bc359/32.png) [@OldGuy](https://boards.straightdope.com/u/OldGuy)\ **Post date:** [January 15, 2013, 4:08am UTC](https://boards.straightdope.com/t/species-extinction/647035/7 "2013-01-15T04:08:26Z")
Most extinct species are likely to be evolutionary branches with no living descendants. > [@Musicat](#): > > I’d say that’s pretty much the definition of one. Not at all. An extinct species has no living members but it can have descendants in newer species that are living. Homo erectus, for example is an extinct species, but is thought (at least by some) to be an ancestor species of Homo sapiens, us. Similarly some type(s) of extinct dinosaur species are ancestor species of modern birds. ---
**Author:** ![JKellyMap](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jkellymap/32/15880_2.png) [@JKellyMap](https://boards.straightdope.com/u/JKellyMap)\ **Post date:** [January 15, 2013, 4:44pm UTC](https://boards.straightdope.com/t/species-extinction/647035/8 "2013-01-15T16:44:15Z")
> [@OldGuy](#): > > Most extinct species are likely to be evolutionary branches with no living descendants. > > Not at all. An extinct species has no living members but it can have descendants in newer species that are living. Homo erectus, for example is an extinct species, but is thought (at least by some) to be an ancestor species of Homo sapiens, us. Similarly some type(s) of extinct dinosaur species are ancestor species of modern birds. I think Musicat meant that the number of species which do NOT evolve into other species (or a bunch of other species), but rather die out, is so proportionally overwhelming, that we might as well (statistically speaking) consider it part of the"definition" of a species, even though you’re right that it really isn’t. ---
**Author:** ![Sailboat](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/sailboat/32/461_2.png) [@Sailboat](https://boards.straightdope.com/u/Sailboat)\ **Post date:** [January 16, 2013, 1:36pm UTC](https://boards.straightdope.com/t/species-extinction/647035/9 "2013-01-16T13:36:26Z")
> [@JKellyMap](#): > > I think Musicat meant that the number of species which do NOT evolve into other species (or a bunch of other species), but rather die out Uh…no species evolves into another species “rather than” dying out. Species is a murky concept, but when what we agree is a species is gone, it can have descendants or not, but it’s still gone. And many species that have descendants or species split-off from them are still extant at the same time as their ancestor/originator species. It’s not at all necessary for a species to die out and be replaced by descendants; in fact, probably most of the time there’s a period of overlap where Original Species and New Species both exist. ---
**Author:** ![Peremensoe](https://avatars.discourse-cdn.com/v4/letter/p/ce7236/32.png) [@Peremensoe](https://boards.straightdope.com/u/Peremensoe)\ **Post date:** [January 16, 2013, 1:49pm UTC](https://boards.straightdope.com/t/species-extinction/647035/10 "2013-01-16T13:49:25Z")
For example speciation often happens when a subset of a given species becomes isolated in a somewhat different environment. There’s no reason that the original population should be wiped out at the same time. For that matter, there’s no particular reason to suppose that the newer species will be the more successful one long-term. ---
**Author:** ![Saraya](https://avatars.discourse-cdn.com/v4/letter/s/b3f665/32.png) [@Saraya](https://boards.straightdope.com/u/Saraya)\ **Post date:** [January 16, 2013, 3:33pm UTC](https://boards.straightdope.com/t/species-extinction/647035/11 "2013-01-16T15:33:56Z")
> [@scoutdad](#): > > I have read that there are anywhere from 2 million to 100 million nonmicrobial species on this planet, with one supposed best estimate of 8.7 million. I have also read that an estimated 99.9% of species that ever lived are extinct. Surely we don’t have fossil remains of eight billion or so extinct species. So how do we know that such a high percentage of species that ever lived have gone extinct? Zoology (can I use that term in this case?) is ridiculously complex - so much so it makes an astronomer’s head spin. Most of what they think they know really is an estimate built off a time line model looking for consistencies and patterns. I find the misconception people have is that ‘species’ (for example), means a single type of animal and we of course then imagine it in it’s modern form. There may actually be a lot of descendants which we do not associate with it, because that ‘species’ already died out.