[Taxacom] Evolution of human-ape relationships remains open...
Richard.Zander at mobot.org
Mon Aug 8 08:38:11 CDT 2011
You have actually two replies to my query.
First, you do answer directly and posit a common ancestor of man and orangutans similar to humans and orangutans. But you imply that it is not a direct common ancestor. In which case I am flummoxed. In the past, in answering the same question, you indicated that there was insufficient information to decide what the ancestor of humans looked like prior to the split to chimps, which is fine. No adduction possible.
Second, you then lose the thread and begin to use Markov reasoning, namely that morphological and molecular data about today's organisms can tell you everything you want to know (as long as the analyses are kept separate or are combined so one overwhelms the other). You do not distinguish between molecular and morphological clades, which are different, and are different views of evolution. If you only discuss clades (leaflets on the tree of life) you cannot discuss macroevolution (stem taxa changing one into another). Clade discussions cannot answer my question, which is which of the two scenarios I game is more probable (or is there another macrovevolutionary scenario, maybe involving some intermediate morphology), and what evidence is there for any of this? None? If so, then discussing clades (present-day nesting of taxa) does not and will never help.
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Richard H. Zander
Missouri Botanical Garden, PO Box 299, St. Louis, MO 63166-0299 USA
Web sites: http://www.mobot.org/plantscience/resbot/ and http://www.mobot.org/plantscience/bfna/bfnamenu.htm
Modern Evolutionary Systematics Web site: http://www.mobot.org/plantscience/resbot/21EvSy.htm
From: taxacom-bounces at mailman.nhm.ku.edu [mailto:taxacom-bounces at mailman.nhm.ku.edu] On Behalf Of Kenneth Kinman
Sent: Sunday, August 07, 2011 10:24 PM
To: taxacom at mailman.nhm.ku.edu
Subject: Re: [Taxacom] Evolution of human-ape relationships remains open...
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
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
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?
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