I would like to see more details than we have had so far. I am trying to construct a simple example of what might happen to produce separate species without mutations. Can others help to make this clear and sensible?
Population Splitting and Evolution
Let's presume we have a population of 2,000 individuals. They have 10 genes in their genome. Label these A through J. Each gene has 5 alleles A1, A2,... D1,D2,D3... through J5. The alleles are not evenly spread:
A1, B1, C1, D1...
50 %
A2, B2, ...
20 %
A3, B3, C3...
10 %
A4, B4...
10 %
A5, B5, C5...
10 %
Now let's imagine that an earthquake creates a huge chasm splitting the population into exactly two equal groups. There are a number of possible scenarios:
1: The group was ranging over their home area randomly and there was no special bunching of animals with a particular allele.
At the end of the split the percentage of each allele in each group is exactly the same. Now each population has 400 individuals with A1 and B1 and C1 ... instead of the 800 individuals that were in the total population of 2,000 animals. The genetic diversity is exactly the same as the original population is it not?
2. One the other extreme could be a split (by chance or for some other reason) where all of one allele fell on one side of the chasm. This could happen to various degrees for each allele.
Now we may have a northern population that has 100 % A1 and zero of A2,A3, A4 and A5. That is the 1,000 amimals with A1 all ended up in the north. It may also by chance have 40 % of B2 that is all of the individuls with B2 ended up in the north.
The souther population would now have zero % A1 and 40% A2, 20% A3, 20% A4 and 20% A5 in the 1,000 animals there.
This in some mix or another could apply to each allele.
3. Intermediate Mixes
Any intermediate mix could happen also but I don't think they matter for this discussion.
I think that Faith's argument isn't based on scenario 1 at all. If that is wrong I'd like to see it corrected.
So let's look at scenario 2. There are no alleles lost in the total population. The genetic diversity of the 2,000 animals is exactly as it was before the earthquake.
However, the northern animals have zero diversity in gene A and the southern animals have reduced diversity in gene A.
Does this make the two populations different species? It can't, mixed back together it is exactly the same 2,000 animals from before.
What possible combination of allele resulting from splitting the original 2,000 animals can produce a different species? It seems to me that none can.
All possible combination of the different alleles of each of the 10 genes were allowed and fertile before the split. Now that we have two separated populations each with reduced diversity what must happen to make the northen and souther populations no longer interfertile?
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