What i can't understand about evolution....

This doesn't need a reply but please read.Just one small point Peg. I'm sure lots of people will cover the main body of the post and I'm not trying to nit pick but I would say this is fairly important. You use the phrase 'perfectly adapted to their environment' which gets used a lot when talking about diversity and evolution.There has never been a 'perfectly' adapted organism for three reasons.Firstly enviroments change so characteristics which were selected for in a previous generation may be a hinderance to the next generation if the enviroment changes.Secondly the variation within a species at any given time limited. Natural selection can only work on what is there so being perfectly adapated is probably outside the possibilities of evolution.Finally many features of organisms are inevitable by products of other features. Not every feature is an adapation conferring evolutionary benefits.If you want me to explain any of these points just ask. I'd say understanding this is critical to understanding evolution as if all organisms were always perfectly adapated to their enviroment there would be no extinction or speciation events and we would have to look elsewhere to explain the diversity of life.Edited by helper, : No reason given.Edited by helper, : No reason given.

Thanks Peg. I can see you've got a lot of replies so I'll just try to explain this. It is incorrect to say they have not evolved. Crocodiles have remained similar phenotypically (in terms of appearance and features) for millions of years. There are phenotypic differences among modern and ancestral species just as there are differences among modern day species today. The crocodile is well adapated but not perfectly so. I pointed out earlier that nothing is perfectly adapated. Evolution has occured as the modern day crocodile species differ both in their phenotype and genotype to ancient crocodile species. In general however crocodiles show stabalising selection whereby the constant enviroment causes selection for individuals that generally maintain the already well adapted features. Evolution is not random. It has no ultimate goal but natural selection gives a short term direction to the process. In the case of the crocodile as I mentioned stabilising selection has caused relative similarity for millions of years.

Hello again Peg, I'll try to clear this up. Mutations are random and create the variation within populations. The alleles are then acted upon by genetic drift (again random) and natural selection (not random). Natural selection is the driving force of evolution and therefore in the short term - that is from one generation to the next - evolution is not random. The long term effects of natural selection are however unpredictable.Hopefully that clears up the situation. Aspects of evolution are random however aspects are controlled. It is incorrect to say it is a completely random process. As I mentioned in the case of crocodile species a form of natural selection (not random) - stabilising selection - has almost certainly occured. It is not random that crocodiles have remained largely similar after a large period of time and it is perfectly in line with evolution. The implication of direction is correct - the direction given by natural selection.Now here is my question to you Peg. Do you understand how stabilising selection would be able to maintain crocodiles as phenotypically similar species over a vast period of time? If not I will explain in more detail.