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Originally posted by NeoPhono Actually, from what I know, the number of species is not a constant. There are certain periods in earth's history where you have a relatively large amount of species, compared to other times. And then there are the 5 major extinction events as well. Maybe this graph will show it a little better.

So are we due then?

___________________
"...End? No, the journey doesn't end here. Death is just another path...one that we all must take.
The grey rain-curtain of this world rolls back, and all change to silver glass...and then you see it...
...white shores...and beyond...the far green country under a swift sunrise."

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Originally posted by NeoPhono Actually, from what I know, the number of species is not a constant. There are certain periods in earth's history where you have a relatively large amount of species, compared to other times. And then there are the 5 major extinction events as well. Maybe this graph will show it a little better.

Interesting. Judging from the graph, however, it seems that the number of species is generally increasing unless some extinction event takes place. Seen in that context, it is either odd that the number of species is currently dropping, or we may conclude that humans constitute an extinction event.

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Originally posted by trancaholic Interesting. Judging from the graph, however, it seems that the number of species is generally increasing unless some extinction event takes place. Seen in that context, it is either odd that the number of species is currently dropping, or we may conclude that humans constitute an extinction event.

Do we know that the total number of species is on the decline?

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Originally posted by NeoPhono Do we know that the total number of species is on the decline?

I was originally going to say yes, because the amount of time (measured in generations) it takes for a new species to emerge would be too long for new species to replace the ones recently made extinct, but then I stumbled across this article:

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New animal species can emerge much quicker than previously thought, say scientists. Salmon in a US lake split into two separate populations in just 13 generations, or about 60-70 years, researchers have revealed. Until now, it was believed that new species took hundreds or thousands of years to appear. And, in a separate study, insects were found to alter the way they attracted a mate in just nine generations. The salmon study took place in Lake Washington, Washington State. The fish were first placed there in 1937. Since then, they have split into two separate populations which prefer not to breed with each other. One group adapted to breeding in a river environment. The others laid their eggs on the lake's beaches. As a result, the two populations have developed slightly different physical features. The male river fish evolved shallower bodies that are better for swimming through strong currents. The female river fish were bigger than the lake ones and able to dig deeper nests. The new evidence suggests that animals can adapt to new environments about 10 times faster than once thought. Researcher Dr Andrew Hendry of the University of Massachusetts, Amherst, who led the study said: "This should really make us rethink the importance of natural selection and adaptation to the rapid generation of new species and the generation of biological diversity." In a separate study, researchers at the University of Queensland, Australia, looked at an insect, the fruit fly. They found that male fruit flies altered the chemicals they use to attract mates after nine generations. The flies appeared to have evolved mechanisms to identify females of the same species, to improve their chances of breeding success. Both studies are reported in the journal Science.

http://news.bbc.co.uk/1/hi/sci/tech/979950.stm

I would still argue that the rate of extinction would be accelerating faster than the possible rate of speciation (presuming that the 500 extinct species in 4 years figure is accurate) and that the breeding rates of larger animals would preclude the possibility of the emergence of any new major species of animal (capable of adapting to the changing environment) in the next few centuries, but at least there's some hope there I guess. In the words of Ian Malcolm, one can only hope - if human beings don't do something soon to protect the global environment - that "life will find a way".

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Originally posted by Renegade I would still argue that the rate of extinction would be accelerating faster than the possible rate of speciation (presuming that the 500 extinct species in 4 years figure is accurate) and that the breeding rates of larger animals would preclude the possibility of the emergence of any new major species of animal (capable of adapting to the changing environment) in the next few centuries, but at least there's some hope there I guess.

I agree. Especially the last part about the rarity of new large animal species. However, I was thinking about whether "artifical" species (such as those that are outcomes of selective breeding) counts as new species? In that case, genetically modified animal species may in the span of a few hundred years offset the supposed(?) drop in species the last thousand years. Assuming that they do not replace existing species that is.

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The fish were first placed there in 1937. Since then, they have split into two separate populations which prefer not to breed with each other.

This quote left me a little confused: I thought that the definition of sharing species was the ability to breed? In that case the two populations of salmon cannot really be said to be different species if they only "prefer" not to breed with each other. In which case the article's conclusions seem dubious.

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Originally posted by Renegade http://news.bbc.co.uk/1/hi/sci/tech/979950.stm

That is so neat.

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Originally posted by trancaholic This quote left me a little confused: I thought that the definition of sharing species was the ability to breed? In that case the two populations of salmon cannot really be said to be different species if they only "prefer" not to breed with each other. In which case the article's conclusions seem dubious.

Wolves/dogs/coyotes/foxes can interbreed under the right circumstances. They're all different species though.

http://en.wikipedia.org/wiki/Canid_hybrid

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Originally posted by trancaholic This quote left me a little confused: I thought that the definition of sharing species was the ability to breed?

So did I, but apparently the science of taxonomy has progressed somewhat since us old bastards last studied it at school.

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Labels require definitions, and species is a very particular label that has been defined in different ways through the past. It first just meant a distinctly-describable type; then it was distinct types that could not interbreed; then it was distinct types that could breed and produce offspring that themselves could go on as adults to breed (some crosses between species can produce young, such as horses and donkeys producing mules, but they grow up to be sterile adults). Today, the best, latest, nontechnical definition of species is... Species: A group that, in natural surroundings, breeds exclusively within the group. In effect, we now let the organisms themselves determine what belongs to their species and what doesn't. This still is not a great definition - it says nothing about asexual species. And, like almost any biological definition, it still has exceptions, such as with coyotes, dogs, and wolves, which can and do interbreed (but not commonly) and are definitely considered separate species. But it works fairly well.

http://faculty.fmcc.suny.edu/mcdarb...ssification.htm

Doesn't seem like a precise science, but I guess under this definition the salmon could be considered different species without too much controversy?

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Originally posted by Renegade So did I, but apparently the science of taxonomy has progressed somewhat since us old bastards last studied it at school.

Sadly. They give you knowledge - and they can take it away in an instant.

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Originally posted by Renegade Doesn't seem like a precise science, but I guess under this definition the salmon could be considered different species without too much controversy?

Yep. I do wonder how the chart Neo posted was created, though. If the new definition is taken as valid, how would anyone know how many species there were even a million years ago?