Quote:
Originally Posted by slappyjenkins
No I tought this was simple enough for you to follow...one species can not mate with another, a dog can only mate with another 100 percent dog...or maybe you believe a dog can hump a cat and make Puppy-Kittens?? Is that true? Is that what you believe? The line isn't arbitrary, when you can't mate with it, its no longer in your species.
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Groups within species can genetically diverge from eachother and follow different evolutionary paths. Many mechanisms that lead to this have been studied and are being studied and many of them are quite complex. The simplest to understand is when a population of a species becomes geographically isolated from others of its kind. They end up in a different environment, with different mutations and evolution puts them on a different path which causes them to diverge. The Galapagos finches is a famous example of isolated, diverging populations of finches on different islands and is one of the observations that really put Darwin on the trail of evolution.
Species can also differentiate without geographical isolation and many such examples exist as well, but they are often more difficult to understand because they typically require more about knowledge about evolution and other aspects of biology. One relatively simple example of such "sympatric" speciation could be if two different strategies (which are coded for genetically) evolve in a population. Merely to illustrate, let's say you have a species of birds where some birds specialize at eating seeds from pine cones while another eats nuts. Both birds are the same species and can mate, but they still have slightly different beaks, one which has evolved to be more effective at picking pine seeds and another which is good for eating nuts. Now, if two such birds breed, they will have an offspring which is a sort of hybrid between the two strategies. This hybrid will have a sort of intermediate beak which is worse for eating either of the two foods, pine seeds and nuts. So hybrid intermediates fare worse than purists of the two strategies. For this reason, birds from either strategy maximize their fitness by mating only with other purists. They learn to recognize their own kind and try to prevent breeding with members of the other strategy.
Across the ages, the two populations become more distinct from eachother, both genetically, behaviourally, morphologically, and one day they can't produce sexually reproductive offspring. Then, even you would find it hard not to admit that they've evolved into new species.
