[Taxacom] Evolution of human-ape relationships remains open...

[Kenneth Kinman]

Hi Richard, 
          As for your first hypothesis, I tend to
agree that orangutans and hominids probably originated from a similar
common ancestor (a primitive gibbon or in the immediate stem-group
leading to gibbons). However, I see no evidence that chimps and gorillas

evolved from that same ancestor----unless that "ancestor" is a very
broad paraphyletic stem-group (somewhat similar to basal members of
Kingdom Protista independently giving rise to the unikont Kingdoms and
the plant Kingdom, not to mention Cavalier-Smith's separate Kingdom
Chromista).         
       However, unlike the broader Protista paraphyly leading
independently to two more more independent lineages, I find the evidence

for a unified hominid-chimp-gorilla clade very convincing, so the great
ape phylogeny seems more defined (with just two major groups) in my
opinion (and many other workers): orangutans splitting off first as
sister group to the singular, but problematic hominid-chimp-gorilla
clade (which is problematic mainly as to whether it was hominids or
gorillas which clade exclusively with chimps). So, unlike Protista
(which gave rise to at least two major independent clades), I see the
great apes as something closer to two single paraphylies in succession
(more like sarcopterygian fishes giving rise to Amphibia, and then
Amphibia giving rise to Reptilia).       
         As for your second hypothesis, I don't
understand how hominids could be viewed as a "throwback". I don't see
early hominids as being derived enough to assume that they were a
"throwback" (a reversal into something less derived?). Actually I
suspect the earliest Australopithecus (or its immediate antecedents)
were far more generalized (underived) than later hominids, or chimps, or

gorillas. And these stem members of an "African ape-hominid" clade
probably shared numerous symplesiomorphies (which Grehan and Schwartz
have listed, although labelled as synapomorphies) with the earliest
stem-orangutans.      
        In any case, I still do not believe that Grehan
and Schwartz have identified synapomorphies, but rather
symplesiomorphies. Therefore, their conclusion that orangutans and
hominids form an exclusive clade is probably incorrect (although I see
them as being less incorrect in my view than those who insist that
chimps and hominids clade together, who would no doubt not even label
them symplesiomorphies, but at best, convergences). So I am actually
less critical of Grehan than they are. They would label his
orangutan-hominid grouping as polyphyletic, while I would regard it as
paraphyletic (and thus far less "wrong"). As one who isn't
paraphylophobic, I would not label such a paraphyletic orangutan-hominid

grouping as "unnatural" (but simply as not useful), but those who prefer

an exclusive chimp-hominid clade would clearly label it polyphyletic
(and thus unnatural from almost everyone's viewpoint).     
      Anyway, I cannot see any scenario where everyone is right in this
debate.  When a future series of papers on whole genomes of the great
apes are published and debated and then further debated, there will be
winners and losers, by which I mean that which particular apes (gorillas

or hominids) exclusively clade with chimps becomes very clear to the
vast majority of scientists.  And if it is gorillas and chimps clading
together exclusively, there would still be the problem whether
orangutans and hominids clade together, or if they split off
successively as separate clades before the chimp-gorilla clade.   
            ------ Ken Kinman           
---------------------------------------------- 
Richard Zander wrote:   
            For example, two macroevolutionary
theories jump forth as plausible: or[an]g[ut]ans and humans originated
from a similar common ancestor and gorillas and chimps evolved at
different times from that ancestor. Second is that the gorilla and chimp

evolved from a similar ancestor that came out of an orang-type ancestor
and humans are throwbacks to that morphotype. Either theory supports
both molecular and morphological analyses, assuming the analyses are
correct. Rather than proving the other side wrong, why not come up with
data that support a macroevolutionary scenario that allows both to be
right?