🚀 go-pugleaf

In article <1992Sep20.223336.9996@leland.Stanford.EDU> ledwards@leland.Stanford.EDU (Laurence James Edwards) writes:

>Does anyone have a rough estimate of how many generations have transpired
>from the time of our earliest sexually reproductive ancestors (I'm talking
>about very simple organisms here) to the present? I'm just looking for
>something within a few orders of magnitude.

This is a very difficult question.
However, if we estimate a human generation to 20 years, it means that
there are 50000 human generations each million of years.
Hence, the order of magnitude of human generations is 10^4 may be 10^5
depending on what you call "human".
The number of preceding "non human" generations seems to me very difficult 
to estimate. However, it's a very interesting question indeed.

>Also, approximately how many guanine, adenine, cytosine, and thymine
>bases are there in the human genome? How many genes? How about for
>some typical very simple organism that is sexually differentiated?

This a much simpler question.
4 possibilities (as you said) for the nucleotides: G, A, C, T
That leads to 64 possible codons. Each codons is made of three nucleotides.
The order of magnitude of the number of codons per gene is 3 10^2.
The order of magnitude of the number of genes per chromosome is 10^6.
The order of magnitude of the number of genes per human being is 10^7.
The order of magnitude of the number of nucleotides is, therfore:
3 x 3 10^2 x 10^7 = 9 x 10^9
The order of magnitude of the number of nucleotides in E. Coli, a very simple
unicellular organism is 5OO hundred times left than for human being.
The order of magnitude of the number of theoreticaly different human
being is : 4 ^ (9 x 10^9) let say to simplify 2 ^ (10 ^ 10).
It is very difficult to get a feelling about how big is this number.
It is so big that the number of elementary particules in the universe
2 ^ 270 is riduculously small compare to it.