Re: Common descent

David Campbell (
Mon, 8 Sep 1997 13:21:21 -0400

>However, multiple origins of life are possible under a naturalistic
>scenario, so this would not unambiguously test ID versus "methodological
>David Campbell
>I think your last sentence is important enough that we need to take another
>look at a built-in problem with systematics. With the standard models of
>evolution we follow Darwin and others in the idea of common descent so our
>tree/shrub diagrams always lead back to a common stem. We relate all
>organisms by similar characteristics (or differences) but assume a common
>I think that at this point in evolutionary biology we need to rethink the
>common ancestor of the first lineages and think instead of similar chemical
>environments of origin. Maybe the only similarities are that earliest
>organisms were carbon based organisms in the same ocean about 4,000,000,000
>years ago.
The choice of left-handed amino acids, the prevalence of the same amino
acids, the importance of RNA, and the universality of the system of DNA
transcription and translation would all support a common ancestor; however,
there are also many differences among living organisms. The apparently
high frequency (high enough to be a problem, not av everyday occurrence) of
gene tranfer among bacteria is a particular problem in resolving phylogeny
at this level-perhaps independently evolved organisms could transfer
genetic material, making them all look similar.

David Campbell