sss3@ukc.ac.uk (S.S.Sturrock) (01/31/91)
In article <111@tdatirv.UUCP> sarima@tdatirv.UUCP (Stanley Friesen) writes: >..... the discovery of Australopithecus afarensis has changed that, now >even cladists are tending to accept that species as either a direct ancestor, >or a very close relative of our direct ancestor. ...................... > >Note that even the place of A. africanus in our family tree is hardly settled. >Some still consider it a potential ancestor of Homo habilis. > >>Primate evolution is a rather difficult subject due to the sparse >>fossil record, man does not die in very good places! > >Actually, it is by far the *most* complete fossil record of any vertebrate. >Much of the current problems are, in my opinion, caused by the fact that >we are actually picking up subtle geographic variations without having >access to the intermediate populations. I know of no other group were >such a welter of minor variants of all sorts are known. The main problem >is to figure out which variants belong together in one species, since the >variants show extensive discordance in features. (I.e. it is impossible >to generate a consistant cladogram that includes all of them). > HOLD IT, where did you get that? The most complete fossil record of any vertebrate? What about the mammoth, we actually have complete specimens of that. How many specimens of hominid species are there? Not many, no wonder they can't generate a decent cladogram, not that it would mean anything if they did! You said yourself that A. afarensis may be a close relative of our direct ancestor, as I did. What about A. robustus if we are going to discuss hominid evolution, there have been all sorts of mistakes made with that one due to sexual dimorphism. Look, there aren't enough specimens, no matter what you might think. Besides I'm inclined to think that a lot of the problem is due to inadequate dating of specimens. While we are at it, the reason cladistics does not work is because it relies on similarities of morphology, what about homomorphy? Also, how can it be applied to fragmentary remains of hominids? Cladistics relies on primitive and advanced features to produce a tree, the problem today is that all species are equally evolved, they are at the same point in time. Some species may have a primitive feature (according to us) but may also be advanced in other ways. Also, a similar external feature may evolve more than once. I don't object to evolutionary trees but they aren't gospel (come to think of it neither is the Gospel :-) ) Species are just arbitrary groups *we* made, nature couldn't care less! Before you get too anoyed, I am just playing devils advocate, I don't know one way or the other, there are people out there who think they do, I remain sceptical.
sarima@tdatirv.UUCP (Stanley Friesen) (02/02/91)
In article <6781@harrier.ukc.ac.uk> sss3@ukc.ac.uk (S.S.Sturrock) writes: >In article <111@tdatirv.UUCP> sarima@tdatirv.UUCP (Stanley Friesen) writes: >>Actually, it is by far the *most* complete fossil record of any vertebrate. >HOLD IT, where did you get that? The most complete fossil record of any >vertebrate? What about the mammoth, we actually have complete specimens >of that. We may have more complete *individual* specimens of the wooly mammoth, but there are far *fewer* available. I suspect that the combined sample of A. afarensis alone exceeds that of thw mammoth, at least in terms of number of individuals represented. (This is largely due to the discovery of a mass-death site containing all or most of an A. afarensis band.) Then, when you add all of the Asian Homo erectus specimens, the African and European sapiens-erectus intermediates, the Neandertals, and the various early Homo sapiens specimens and you have an impressive record. > How many specimens of hominid species are there? Not many, no >wonder they can't generate a decent cladogram, not that it would mean anything >if they did! I agree with the latter. And in some senses it is true that we do not have 'enough' specimens, since there is no such thing as 'enough'. But the evolutionary trees (and species boundroes) have been getting *more* not less clear as we get more specimens. I have been trying for over a year to come up with a satisfactory division of the early African Homo specimens into species. (These are the specimens usually considered as Homo habilis and earliest Homo erectus). There appear to be at least four different morphs included in the group (perhaps five). Now, are these geographic or temporal variants of a single species, or distinct species. Some of them almost certainly are distinct species, since two of the morphs co-exist in the same beds. Of course this *could* be sexual dimorphism. But if it is why do the other sites only have one morph each? All in all a ticklish problem, and one that would not exist if we had fewer specimens, since the bimodal ditribution would not be visible with a smaller sample. (Nor do we have so many seperate fossil sites in so small a time-space volume for any other group of vertebrates). >You said yourself that A. afarensis may be a close relative of our direct >ancestor, as I did. What I heard you to say was that it was firmly established that it was not a direct ancestor. This is not so. And if it is not, it is *extremely* close to it, so close that it might not be distinguishable in the fossil record. > What about A. robustus if we are going to discuss >hominid evolution, there have been all sorts of mistakes made with that >one due to sexual dimorphism. Look, there aren't enough specimens, no >matter what you might think. Besides I'm inclined to think that a lot of >the problem is due to inadequate dating of specimens. A. robustus, or as I call it Paranthropus robustus, is clearly a side branch, as are all of the robust 'autralopithicines' (P. aethiopicus, P. boisei, and perhaps one or two other species depending on interpretation). [Hmm, here we have it again, slight differences in features between closely spaced samples - one species or two?] > Species are just >arbitrary groups *we* made, nature couldn't care less! Before you get too >anoyed, I am just playing devils advocate, I don't know one way or the other, >there are people out there who think they do, I remain sceptical. Hoo boy, as far as I am concerned, *species* are the *only* taxonomic category that is truly 'real', in the sense that it corresponds to an actual entity in nature. All of the other categories, both higher and lower, are indeed arbitrary to some degree. [Even in cladistic analysis, since I have never seen two cladistic analyses that agree unless they were by the same author]. -- --------------- uunet!tdatirv!sarima (Stanley Friesen)