Re: Does two people constitute a viable gene pool?

There is the scientific point of view and the theoretical point of view. I 
will tell you both and you can decide what you want to believe.

The scientific point of view is based upon the simple fact that all human 
beings are mutants. What do I mean by this? All human beings have mutations 
in their genes in one place or another. These mutations have detrimental 
side effects if any one person has too many mutations. So if I take one 
million mutants that each have say 5 mutant genes, and allow them to 
produce offspring at random. Most of the time any one person will only have 
5 mutant genes, many will have 6, some will have 7, and a few will have 8. 
And there will be very few that have more than 8. Remember for the most 
part the more mutant genes you have as an individual the less viable you 
are. This is a fundamental law of nature.

Now there is another fundamental law that comes into play. Individuals tend 
to each have different mutations. So Jack may have mutant gene A, B, C, D, 
and E. But Jill will have mutant gene F, G, H, I, and J. So when Jack and 
Jill mate their children get some combination of these mutant genes. Thats 
OK, because they go meet some random individual with mutant genes K, L, M, 
N, and O. Thus the offspring still of Jack and Jills children still have a 
chance of getting replacement A-J genes if they have a defective copy.

Now lets talk about small populations. We start with two people with 5 
mutant genes each. Lets say for argument 8 mutant genes is fatal. Now they 
each have 5 mutant genes, and their children will each have about 5 mutant 
genes. Thats OK.
So 	Jack 	ABCDE
	Jill	FGHIJ
	kids:	#1:AGCIE, #2:BDFGHI, #3:ABIJ, #4:GHDEF

Now we see that randomly 2 kids got 5 mutant genes, 1 got 4, but 1 got 6. 
But it is OK they are viable. Now lets have #1 and #2 have kids:
so	#1	AGCIE
	#2  BDFGHI
Now a rule is that if both parents have a gene - all the  kids get it.
Here both parents have G and I.
 kids: #5:GIBDA, #6:GIABEHC, #7:GIAH, #8:GIEF

Now we are still OK so lets have #5 and #6 get married:
so 	#5	GIBDA
	#6 	GIABEHC	 
both parents: GIBA
	kids: #9:GIBADEH, #10:GIBAHC, #11:GIBDAEHC(fatal), #12:GIBAEC

Now we are not OK. We are starting to have fatal mutations. So you see a 
population starting with two mutant people will always lead to accumulation 
of mutants in the offspring which will have deleterious side effects. This 
is a fact of life.

That is the scientific point of view, now on to the theoretical point of 
view.


The scientific poit of view is that you can not start with two people. This 
assumes that you start with two people that are "normal", that have many 
mutant genes. But theoretically speaking what if you start with two people 
that are "perfect" have absolutely no mutant genes. If you start this same 
experiment, now with mutant free parents:
Jack - no mutants
Jill - no mutants
Kids 1,2,3,4,5,6,7,8,9,10

your OK, kid 1 marries 2
kids of 1 and 2:  21,22,23,24,25,26,27,28, 29:A

Now person 29 had a random mutation. These happen infrequently. We now have 
our first mutant in the gene pool.

So 29 marries 22
kids of 29 and 22: 31, 32:A, 33, 34, 35:A, 36, 37, 38, 39

So now we see that mutations begin to accumulate. But remember what is 
happening at the same time here.
First generation: 2 people Jack and Jill
2nd:	10 people (ie 5 mating pairs)
3rd:	40 people (ie 20 mating pairs, 2 people with one mutant)
4th:	180 people (ie 90 mating pairs, 6 people with one mutant)
5th:	800 people (ie 400 mating pairs, 30 people with one mutant, 1 with 2 
mutants.)
6th:	3800 people (ie 1900 mating pairs - more mutants)

So you can see theoretically you can increase your populations size 
sufficiently before you start to accumulate too many mutants in the gene 
pool. Thus you can get to your one million people before everyone has five 
mutants each. 

That is the theoritical point of view though. You have to assume that what 
you started with was perfect.

Now if you want to be controversial and put the theoretical view in the Adam and 
Eve perspective. First lets look at how long people lived. Adam and Eve lived 
over 800 years, and their children/ grandchildren etc lived about that long. Now 
say that they had a child once every three years - just for fun - so that means 
the had about 200 children, spread out over about 600 years. Now if there first 
born child didn't start having children until they were 100 and stopped when 
they were 700, and died at 800 - their first born would have about 200 children, 
130 of which would be the same age as the children of Grandma and Grandpa. So 
you might just marry your uncle under those circumstances. This would serve 
early on to keep the number of mutations in any one persons offspring very low. 
But mutations would eventually accumulate. I am not a theoretical geneticist so 
I don't know how long it would take to accumulate sufficient mutants to make it 
no longer possible to survive a bottleneck.

Don't forget about the Noah bottleneck. That was three sons of Noah, married to 
three different women. So that was a starter of essentially four people.

David