Some aspects of speciation and extinction

[pressld2]

Originally Posted by animartco

It is just that, as you say, in their present state they are non viable and unless domesticated again, will soon be extinct.

Hi Gillian,

As Ric has pointed out, I certainly didn't say that! Cheetahs are a perfectly viable species in their current environment. All I'm saying is that if and when that environment alters they would be less well able to cope with this through evolutionary adaptation than would other African big cats with more variation in their gene pools. But the cheetahs might still pull through.

It seems likely that the reason for the cheetah's lack of variation within the gene pool is that they went through a "genetic bottleneck" about 10,000 years ago when the species very nearly became extinct. This meant that there was significant in-breeding within the population that was left, hence the low-variation levels today. But with every generation that passes, cheetahs are once again building up variation within the pool and, if given long enough to recover from the bottleneck, they'll be fine.

Originally Posted by Brocakat

I seem to remember reading about Charles Darwin and his studying of a specie of birds which, whilst looking the same in body-shape & size / colouration - had evolved different beaks, for utilising the individual - but separate-from-each-other Islands ( was it the Galipagos ? ) food-sources.

Spot on! It was the Galapagos finches that Darwin noticed were each adapted to eat the food available on the island they lived on. Nowadays it's often the differences in the Galapagos giant tortoises that get talked about the most but it was definitely the finches that made a big impression on Darwin.

Dave P.

[RoyW]

Originally Posted by davecatt

RoyW
I read your ref' and concluded that your answer should have been yes its all theory: Why dose it matter? Do we really need to Know?

Yes, it's all theory - in the same way that cell theory, gravity, and plate techtonics are all just theory.

Speciation is not something that can easily be directly observed, but the theories are extremely well supported by a wide variety of different observations and discoveries (including things like DNA analysis - despite DNA and genes being unknown at the time Darwins theory of evolution was first published). Note that I am using the scientific meaning of "theory", which is an explanation based on observation, experimentation, and rational consideration of all proveable facts, which has been tested and can be used to predict phenomenon. I do not mean it is "just an idea" which is the meaning that theory tends to have in everyday language (in science an untested and unproven idea is a "hypothesis"). In science you often can't get any higher than a theory (laws apply only when you can define something mathematically) - and evolution is one of the best supported theories that there is.

Originally Posted by davecatt

Why dose it matter? Do we really need to Know?

If we truely want to understand the natural world, and how the huge variety of organisms have come to be then yes we do need to know (and in many cases understanding can help with the conservation of species).
Can we survive, and enjoy life & the life around us without knowing? Of course we can, and a large proportion of the worlds population know very little about these theories but live just as well as those who do, so we don't really need to know - but then how much do we really need to know abou most of the things that interest us?

Originally Posted by pressld2

Spot on! It was the Galapagos finches that Darwin noticed were each adapted to eat the food available on the island they lived on. Nowadays it's often the differences in the Galapagos giant tortoises that get talked about the most but it was definitely the finches that made a big impression on Darwin.

It is generally considered that it was actually the mockingbirds on the Galapagos Islands that were most important in Darwins development of his theories of speciation by common decent. He recognised, and collected, three different species on the islands (with a fourth endemic species found much later), all with noticeable differences from each other, and species on the South American mainland.

[pressld2]

Originally Posted by RoyW

It is generally considered that it was actually the mockingbirds on the Galapagos Islands that were most important in Darwins development of his theories of speciation by common decent.

Seems like I'm behind the times on this one Roy! I've just googled for "Darwin mockingbirds" and got a whole bunch of results all dating from around November 2008 (and another bunch from November 2009). All my books mention the finches (and the tortoises) but not the mockingbirds. Except for On the Origin of Species itself, that is, in which Darwin talks about "mocking-thrushes" in the second of the chapters on geographical distribution.

Dave P.

[STYRBJORN]

For an excellent popular account of modern research into the ongoing evolution of the Galapagos finches see The Beak of the Finch Jonathan Weiner, Jonathan Cape1994.

Probably out of print, but worth a bit of effort to track down a copy.

Ric