Gothmog
Dread Enforcer
- Joined
- Sep 19, 2002
- Messages
- 3,352
Geographic barriers are one good method, however even without that a 'duck' could not breed with a chicken... or whatever.
Methods of reproduction, especially sexual ones, are very detailed and specific. It really doesn't take much change for reproduction to become impossible. Experiments in fruit flies have shown that simply changing the temperature, or certain other aspects of the physical environment, at which the flies breed for a couple hundred generations can result in two groups that can no longer breed together.
The point is that even if we call two forms of life a 'species' in the fossil record (say separated by a few million years), there is no guarentee that these lifeforms would be able to interbreed if somehow brought together today. The change in genomes is continuous, mutations are always being introduced and others eliminated.
Here's a quote I found on the shifting nature of the term 'species':
Methods of reproduction, especially sexual ones, are very detailed and specific. It really doesn't take much change for reproduction to become impossible. Experiments in fruit flies have shown that simply changing the temperature, or certain other aspects of the physical environment, at which the flies breed for a couple hundred generations can result in two groups that can no longer breed together.
The point is that even if we call two forms of life a 'species' in the fossil record (say separated by a few million years), there is no guarentee that these lifeforms would be able to interbreed if somehow brought together today. The change in genomes is continuous, mutations are always being introduced and others eliminated.
This is silly and shows a basic lack of understanding about the nature of genetic change. There is no real difference between micro and macro evolution, they are semantic lables used primariliy in cladistics and held over from when the fossil record was our best evidence for evolution. In terms of genetics there is no difference. If a 'micro' change can spread through a population, which you accept, why can you not accept that a large number of 'micro' changes over a long period of time (or a period of shifting environmental variables, whether due to climate change or migration) can result in a group that can no longer breed with the previous group? All it takes is for some of those 'micro' changes to be involved in the reproductive process. Easy cheesy, new species (assuming we define species by reproductive success, actually it is hard to define exactly what constitutes a new species - it is somewhat arbitrary).The only way it allows for speciation is if many members of the same population experience the same critical genetic mutation, at the same time, which is a contradition of evolution.
Here's a quote I found on the shifting nature of the term 'species':
By Darwin's time, a species was a group of animals that looked similar down to a more specific level. So a group of bluebirds in the eastern US might be considered a different species if they all looked slightly different from a group of bluebirds in the western US.
In the 1940s and 50s, as people learned more and more about genetics and breeding, a species became a group of animals that could breed with each other. Cats were one species, and dogs were another. They both have fur, they both have tails and ears, but they can't breed with another. Note that all dogs are ONE SPECIES even though they can look vastly different from each other. That's because - even while a great dane looks quite different from a dalmation - the two are genetically able to breed and have puppies.
Nowadays, the breeding line is the one most biologists draw. This line can be drawn for two reasons. One, the creatures simply cannot create a viable new baby organism. That would be the case between for examples cats and dogs. Even if you did convince them to mate, their sperm and egg could not join properly. The second situation is *situational* non-viability - where the two groups of creatures never interact properly to mate. This would be the case where one group of black monkeys lives in Africa and another brouwn group lives in Asia. Maybe they COULD mate and make babies if they ever met, but they simply don't.


