Is my calculation correct? (human evolution)

Question

This is a back-of-the-envelope calculation I made to someone who was saying that the chromosome 2 wasn't enough to say we were related to monkeys:

Human and chimp genome have 3x10^9 bps. In the human genome there are 30.000 retroviral insertions, and 7 are shared with the chimp (Bonner et al. 1982; Dangel et al. 1995; Svensson et al. 1995; Kjellman et al. 1999; Lebedev et al. 2000; Sverdlov 2000). Calculating that a retroviral happens on average every 3.000.000/30.000 = 100 bp, we have 1/100 chance that this insertion happened in both man and chimp by chance. Since the 7 insertions are indipendent events, overall probability 1/100^7 = 1/10^14.

Question(s)

Am I doing this right?

Did anyone else already do this - better? Where can I find it?

Insertions are directional, how could I take this fact into account? Thanks in advance.

Answer 1

There is a discrepancy in your numbers.  You say 3 x 10^9 bps but then later (when you write 3.000.000/30.000) you change it to 3 x 10 ^6.  

If the 3 x 10 ^ 9 figure is correct, your final answer should be

1/10000^7 = 1/10^28

You want to take the fact that insertions are directional into account, but isn't that what you are trying to prove?

Your reasoning seems sound to me, but I fear that will be of no interest if your friend is a fundy.  Faced with hard scientific evidence they will cover their ears and eyes just like those "Hear no evil" monkeys, which obviously they have no relation to whatsoever.

Answer 2

Your computations seem fair to me ... and that is some back-of-the-envelope calculation!

But back to your first sentence.  Why does your friend say that Chromosome 2 is not enough evidence of even a *relationship* between humans and apes?   (Forget monkeys for the moment.)  

Is your friend claiming that the evidence  (such as the telomeric DNA in the middle of the Chromosome) that Chromosome 2 is a fusion of two chromosomes found separate in the ape genome is insufficient?   Or that such a fusion, even if demonstrated, does not constitute evidence of relationship?

Because either way, if your friend rejects the evidence of Chromosome 2, which is as close to a slam-dunk smoking gun as you can get, then all these complex combinatorial probabilities will be falling on stubbornly deaf ears (like those of Ivan M here, and those who quietly thumb him up as a "good answer" to this question).

Answer 3

God created everything.