In article <EDDY.95Oct7085053 at wol.wustl.edu>,
Sean Eddy <eddy at wol.wustl.edu> wrote:
>>This is no problem, so long as the origin of life is probable, or the
>Earth was lucky. But if it turns our that there just has to be a few
>billion years for a massively complex life form like the last common
>ancestor of Earth life to arise, it might become necessary to explore
>the possibility that life arose on another, older world.
>>Not that the hypothesis is testable, mind you.
Of course it is!!!! There are a number of proteins (glutamate
dehydrogenase is perhaps the best candidate) with rates of change that
allow us to look back much longer than 10By, the putative age of the
universe. See:
%A R. F. Doolittle
%A D. F. Feng
%A M. S. Johnson
%A M. A. McClure
%D 1986
%J Cold Spring Harb. Symp. Quant. Biol.
%V 51
%P 447-455
%T Relationships of human protein sequences to those of other organisms
All we have to do is sample a life form from outer space, and the
question could be answered quite quickly (I would be convinced if they
had the same 20 amino acids I think).
Bill Pearson
--
wrp at virginia.EDU
Dept. of Biochemistry #440
U. of Virginia
Charlottesville, VA 22908
