human origins

Thu Jan 22 16:20:13 CST 2004

At 10:57 AM 1/22/04 -0600, Richard.Zander at MOBOT.ORG wrote:
>Well, hang on a minute there. The molecular data are commonly sufficient to
>allow statistical tests of reliability but morphological data are generally
>not. It isn't just "genetic sequence similarity" to the exclusion of
>morphological data.
>Naturally, the presumption is that if random generation of parallel traits
>in closely related but not sister lineages is not to be expected by chance
>alone, one can assume shared ancestry of apparent sister taxa.

But why shouldn't we expect it by chance alone?  If, for example, each gene
is expected to mutate once per million cell divisions, and that gene is
present in two closely related but not sister lineages, it would be
expected to mutate once per million cell divisions in each lineage.  So
although the probability goes down, it would be expected to happen again
eventually in a parallel manner.  This is true independently of natural
selection.  So if one lineage can survive with the mutation, it isn't
surprising if another can too.  I know not all mutations of a gene are
identical but some are.

>This is not
>exactly true since coadaptive traits associated with habitat may also force
>parallelism (pointed out by Landrum, Rensch and doubtless others) and thus
>confound at least details of a cladogram. Both morphology and exons are
>liable to this problem, I believe.
>Statistcally impressive results from introns and junk DNA are hard to
>explain away.
>-----Original Message-----
>From: Ronaldo [mailto:ralperin at TERRA.COM.BR]
>Sent: Thursday, January 22, 2004 4:06 AM
>Subject: Re: [TAXACOM] human origins
>Hello John,
>Wednesday, January 21, 2004, 1:23:53 PM, you wrote:
>"So in conclusion the paper is fairly representative of what I am reading
>  in general. The chimpanzee relationship is presented as a fact. It is
>  based on the presumption of genetic sequence similarity being the whole
>  truth of phylogeny, and morphological considerations are rendered almost
>  a foot note with the consequent lack of rigor in any connection being
>  substantiated between living humans and other apes and purported fossil
>  representatives. "
>  Fully agreed! John, here in Brazil we have the same situation with
>  the primates in general. Just see the huge number of papers regarding
>  "Phylogenetic" relationships among Neotropical Primates. I have to
>  ask; "Phylogenetic" or Molecular (with no explicit criteria)
>  relationships?
>  Ronaldo Alperin
>JG> John Grehan
>JG> Dr. John Grehan
>JG> Director of Science and Collections
>JG> Buffalo Museum of Science
>JG> 1020 Humboldt Parkway
>JG> Buffalo, New York 14211-1293
>JG> Voice 716-896-5200 x372
>JG> Fax 716-897-6723
>JG> jgrehan at
>Best regards,
>  Ronaldo                            mailto:ralperin at

Stephen D. Manning, Ph.D.
Professor of Biology
Mathematics and Science Division
Arkansas State University - Beebe
P. O. Box 1000
Beebe, Arkansas 72012-1000
Tel: 501-882-7162

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