[vaniotia]

How does species divergence occur in the process of normal evolution if both a male and female are required to perpetuate a new species? Isn't the odds of them both occuring spontaneously, at the same time, almost nil, aside from a twin pairing? I am not suggesting any other explanation, but I am curious what is to be said about this.

[CharonY]

Speciation is a) not a spontaneous process, and b), as in all evolution, happens within populations. What is usually necessary is that e.g. from a common population (or species, if you want) subpopulations are getting separated and the genetic flow between them is very limited or zero. Over time both populations accumulate different genetic properties that may eventually render them genetically incompatible. At that point the two subpopulations can be considered different species.

[Keenidiot]

Speciation is a gradual process, it doesn't occur immediately. As generations go by, you end up with an organism descended from a species that can no longer interbreed with the original species, but can breed with the generations that preceeded it.
A good example of this is ring species.

In ring species, you have populations that are spread out (the two examples I can think of were along a coast) and the population varies as you move from population to population.
While they can successfully interbreed with populations near to them, there's a point where it cuts off as you move further away from that population, and at either end you'll have completly seperate species that cannot interbreed.

Now, species itself I understand is a somewhat vague. It's used to mean any organism which cannot successfully interbreed in nature.
However, there are animals that can successfully interbreed, though will not do so naturally.
Their offspring will be viable, and can produce later generations.
However, they are two separate species.

This post has been edited by Keenidiot: 10 January 2012 - 10:58 PM

[jeskill]

CharonY, on 10 January 2012 - 06:31 PM, said:

Speciation is a) not a spontaneous process, and b), as in all evolution, happens within populations. What is usually necessary is that e.g. from a common population (or species, if you want) subpopulations are getting separated and the genetic flow between them is very limited or zero. Over time both populations accumulate different genetic properties that may eventually render them genetically incompatible. At that point the two subpopulations can be considered different species.

While speciation is usually not spontaneous, it can occur quite rapidly when polyploidy occurs.

[CharonY]

Good point. I should have mentioned that the mode of speciation that I described is termed allopatric. That and variations thereof are best supported by empirical data. It should also be noted that polyploidy (which can be considered a case of sympatric speciation), is not necessarily more rapid than allopatric speciation. I suppose it is obvious but the occurrence of a single polyploidic mutant would not signify a speciation event. Only if it spreads through the population (and hence, create a divergent population), does it become recognizable as such.
Whether it is faster would depend a lot on the usual parameters, such as population size, frequency, selective pressures, etc. It is correct to state that the number of mutations required is drastically reduced, though.