(December 23, 2016 at 8:15 am)Gawdzilla Sama Wrote:(December 23, 2016 at 7:52 am)robvalue Wrote: It makes sense to me. A species is always naturally tending towards the most efficient form for the environment (although a good degree of junk tends to sneak through the net along with it). So if there's a big change in the environment, there going to be a big gap between the current norm for the species and the new optimum characteristics. Useful changes are going to be more important and so will get factored in faster.
If the environment doesn't change or changes only slightly, the norm won't be very far away from optimum.
Or, y'know, reality is a big lie and it's all done by magicks.
The "next generation is different" idea has problems. First, how many animals have to have the same mutation to produce a successful breeding population? Second, the more likely response to a "big change in the environment" is a mass dying off. If savannah changes to tree-less plain the giraffes are going to have problems. Can they convert to "grazer" quickly enough? Nothing in the fossil record supports this. In fact the fossil records don't show "big change" at any time in one-half billion years. But there's still time, I suppose.
It is exceedingly unlikely that two animals, one male, one female, living at the same time in the same population, experience the same mutation, happen to come together and mate and out pops a new species. That's not how speciation works.
Instead,a heritable mutation occurs first in a single individual. If that mutation doesn't kill the individual before mating, prevent the individual from mating, and its impact sufficiently Limited so it can still produce fertile offspring with other members of its own population, then the mutation has a chance. Otherwise the mutation is self-eliminating.
If the mutation has a chance, then the first carrier of the mutation mates with a noncarrier and passes the mutation onto some of its offsprings. His mutation carrying offsprings then do the same. In time there would be a sizable number of mutation carriers, all can either mate with each other, or still with normal members of the population. Once you have big numbers, probability comes in, and survival of fittest is a game of probability.
If this mutation is harmful, then carriers of this gene would have less success in passing on their genes compared to the broader population. So percentage of population that carry this gene would reach some low threshold and not grow any further. If this mutation is beneficial, then its carriers would have better than average chance of passing it on. In time the entire population would be carrying this mutation.
So how does speciation occur? Well, not solely by the means described above. What is described above is gradual evolution of the gene pool of a given population. The entire population's gene pool shifts subtlety from generation to generation. Beneficial mutations gradually propagate to the entire gene pool, old obsolete adaptations graduallly disappear from the entire gene pool.
For clear speciation to occur, one more thing has to happen, that is the mutation only propagate through parts of the population, not other. If this happens, parts of the population through which mutations propagate will look increasingly different from the rest of the population. Keep this up for tens or hundreds of thousands of generations, the two parts could become so different they can no longer mate to produce fertile offsprings. If this happens, speciation occurs.
How could this happen? One way is geographic separation. For example, Parts of the population lives one one side of the river and the other part on the other side. They seldom are able to cross the river to mate. Mutation happens in one individual on this side of the river, in time the mutation sweeps through the entire population on this side. Eventually, different mutations accumulate this way on each side, until they become two different species. There are many other ways for similar confinement of mutation to sub populations to occur.
