al@gtx.com (Alan Filipski) (01/23/91)
In article <72753@bu.edu.bu.edu> colby@bu-bio.UUCP (Chris Colby) writes: > We, as in humans, are not evolving. Given that just about >about everyone lives to reproductive age and reproduces, natural >selection is not acting on our species. Also, the population size >of human beings is such that genetic drift does not take place. > To be a little more accurate, >some small amount of selection and drift is most likely occuring, >but it is negligible compared to other living species and our exposure I don't have the figures, but I'm sure that the average South American reproduces at a much higher rate than the average European. If you consider the (currently) low birthrates of Europeans, Euro-Americans, and Northern Asians and the high birth rates of American Blacks, South and Central Americans, Philipinos, Pakistanis, etc, I'd say that "we" are getting darker-skinned at a good clip, with all the genes associated with darker-skinned populations increasing in frequency. On the average, darker skinned people (and catholics) thus have greater fitness than WASPS. It's a strange kind of fitness, though, since it is only statistically rather than causally related to genotype. There is nothing, I think, intrinsic that causes a Mexican to have more kids than a Frenchman-- it's just where they happen to be born. Would it be technically considered group selection? I don't have a broad enough knowledge of biology to say whether such frequency change is negligible compared to gene frequency changes in other species. Perhaps so, but only because we live in extraordinary times of very rapid artificial environmental change (A "major extinction event", I forget who has said). Also, I believe that almost any kind of speculation about human selection starts many otherwise objective people frothing at the mouth for political reasons. Maybe this is one of those subjects. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ( Alan Filipski, GTX Corp, 8836 N. 23rd Avenue, Phoenix, Arizona 85021, USA ) ( {decvax,hplabs,uunet!amdahl,nsc}!sun!sunburn!gtx!al (602)870-1696 ) ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
sss3@ukc.ac.uk (S.S.Sturrock) (01/24/91)
In article <1435@gtx.com> al@gtx.UUCP (Alan Filipski) writes: >In article <72753@bu.edu.bu.edu> colby@bu-bio.UUCP (Chris Colby) writes: > >> We, as in humans, are not evolving. Given that just about >>about everyone lives to reproductive age and reproduces, natural >>selection is not acting on our species. Also, the population size >>of human beings is such that genetic drift does not take place. > >> To be a little more accurate, >>some small amount of selection and drift is most likely occuring, >>but it is negligible compared to other living species and our exposure > How the hell can you make such a stupid statement as 'We, .., are not evolving.' Sheesh, that's as bad as the time I had an argument with a Catholic about evolution and she stated that evolution could not possibly happen because if it did, why has it stopped? Your time frame is totally insignificant. Simply, the age of the Earth is thought to be 4600,000,000 years. The earliest life evolved some 3500,000,000 years ago. Eukaryotic life evolved about 600,000,000 years ago, almost 3000,000,000 years later, but this is not a maths lesson. :-) Man, as is now, has been around say 2,000,000 years. Not long is it? You live 80 years tops, very little in fact. Recorded history goes back 6-10,000 years, still not much. GET YOUR HEAD OUT OF THE BUCKET! Evolution takes a long time, but wait, I am 6'3" tall, much taller than people were 500 years ago, you try walking around in a Medieval house without stooping. The average height is much greater than it was then, so that is evolution is it not? Do I smell the foul odour of a Christian pervading the atmosphere of a science newsgroup? :-) Hmmmm? Shane Sturrock, Biol Lab. Canterbury, Great Britain.
szarekw@lonexc.radc.af.mil (William J. Szarek) (01/24/91)
>How the hell can you make such a stupid statement as 'We, .., are not >evolving.' Sheesh, that's as bad as the time I had an argument with >a Catholic about evolution and she stated that evolution could not >possibly happen because if it did, why has it stopped? > [many nice 'facts' removed] > > >Evolution takes a long time, but wait, I am 6'3" tall, much taller than >people were 500 years ago, you try walking around in a Medieval house >without stooping. The average height is much greater than it was then, >so that is evolution is it not? Quite right my friend. you are indeed much taller (if not smarter) than your medieval counterparts. As anybody who has more than skimmed the surface of this topic knows it is due more to better nutrition than genetic evolution. In short, nice rebuttal, 2 points for lots of facts, 2 points for big words, a slap on the wrist for a prejudice attitude (intolerance: the mark of an intellectual), and a big fat goose egg for your use of supportive evidance. Maybe you haven't noticed, but many "Christians" don't run around telling people how to live their lives. Many of us just go about our lives taking care of *our* lives. Sometimes it is what you *do* not what you *say* that makes you *good*. I am a scientist and a Christian. I happen to believe in the theory [myth? :-)] of evolution. The two are not irreconcilable . . . (the hand of God is visable in all things). suma cum grano salis buzz
colby@bu-bio.bu.edu (Chris Colby) (01/25/91)
In article <6735@harrier.ukc.ac.uk> sss3@ukc.ac.uk (S.S.Sturrock) writes: >In article <1435@gtx.com> al@gtx.UUCP (Alan Filipski) writes: >>In article <72753@bu.edu.bu.edu> colby@bu-bio.UUCP (Chris Colby) writes: >> >>> We, as in humans, are not evolving. Given that just about >>>about everyone lives to reproductive age and reproduces, natural >>>selection is not acting on our species. Also, the population size >>>of human beings is such that genetic drift does not take place. >> >>> To be a little more accurate, >>>some small amount of selection and drift is most likely occuring, >>>but it is negligible compared to other living species and our exposure >> > >How the hell can you make such a stupid statement as 'We, .., are not >evolving.' Sheesh, that's as bad as the time I had an argument with >a Catholic about evolution and she stated that evolution could not >possibly happen because if it did, why has it stopped? I never claimed all evolution stopped, merely that the rate of change of human evolution is at the slowest point it (probably) ever has been. Look in the newsgroup talk.origins for my full argument. I did not transfer the small part of my post you quote to this newsgroup. >Your time frame is totally insignificant. An instantaneous rate of change can be calculated for evolutionary processes. The rate is equal to the amount of additive genetic variance in fitness (Fishers Fundamental Theory of Evolution). [Natural History "lesson" omitted] I am well aware of the timescale of evolution. >GET YOUR HEAD OUT OF THE BUCKET! > >Evolution takes a long time, but wait, I am 6'3" tall, much taller than >people were 500 years ago, you try walking around in a Medieval house >without stooping. The average height is much greater than it was then, >so that is evolution is it not? No, actually it is not evolution. Better diet and medicine have caused an increase in human height. If you ate and had the same medical attention as people did 500 years ago you would be their height. The increased hieght is not heritable. >Do I smell the foul odour of a Christian pervading the atmosphere of >a science newsgroup? :-) No, you smell the foul odor of a graduate student studying evolutionary biology. Look in talk.origins or sci.skeptic and see my full line of reasoning before you try to teach me evolutionary theory jerk. And while you are at it, aquaint yourself with various mathematical models of evolution such as the Hardy Weinberg eq- uilibrium, Wrights Adaptive landscape model and (as I mentioned) Fishers Fundamental Theory of Evolution. >Hmmmm? > >Shane Sturrock, Biol Lab. Canterbury, Great Britain.
north@manta.NOSC.MIL (Mark H. North) (01/25/91)
In article <1435@gtx.com> al@gtx.UUCP (Alan Filipski) writes: > >Also, I believe that almost any kind of speculation about human >selection starts many otherwise objective people frothing at the mouth >for political reasons. Maybe this is one of those subjects. > Yes, you better check your little red book on politically correct ideas before you float another one like this. 8^) Mark
sarima@tdatirv.UUCP (Stanley Friesen) (01/26/91)
In article <6735@harrier.ukc.ac.uk> sss3@ukc.ac.uk (S.S.Sturrock) writes: >Man, as is now, has been around say 2,000,000 years. Not long is it? Not really, the earliest members of the Hominidae appeared 2-3 million years ago. This form was essentially an semi-terrestrial, bipedal ape, not very different from a modern chimpanzee. The earliest Homo sapiens appeared about 100,000 to 300,000 years ago, and 'modern' Homo sapiens appeared even more recently than that! Of course this just strengthens your argument, this miniscule span of time is unnoticable on evolutionary time scales. >Evolution takes a long time, but wait, I am 6'3" tall, much taller than >people were 500 years ago, you try walking around in a Medieval house >without stooping. The average height is much greater than it was then, >so that is evolution is it not? No it is not. Evolution (in the biological sense) implies *genetic* change. The change in height from Medieval times is essentially a purely nutritional matter (with perhaps a fair dollop of general improvement in child health care). No genetic change has been implicated in this shift. However there is some indication of evolution in humans on a ~10,000 year time scale. The natives of India are much darker skinned than the natives of Scandinavia, despite both groups being 'aryans' (that is descendents of the original speakers of Indo-European). And this difference most assuredly is genetic, since it is inherited in all environments. In fact this difference is an adaption to the difference amount of sunlight in the two regions. In subtropical India, there is much sunlight, and excess exposure to UV is a problem, so darker skin reduces the cancer rate. In subarctic Scandinavia there is very little sunlight, and insufficient vitamin D production is a problem, which unusually light skin helps to alleviate. -- --------------- uunet!tdatirv!sarima (Stanley Friesen)
ronald@uhunix1.uhcc.Hawaii.Edu (Ronald A. Amundson) (01/27/91)
In article <104@tdatirv.UUCP> sarima@tdatirv.UUCP (Stanley Friesen) writes: > >However there is some indication of evolution in humans on a ~10,000 year >time scale. The natives of India are much darker skinned than the natives >of Scandinavia, despite both groups being 'aryans' (that is descendents of >the original speakers of Indo-European). And this difference most assuredly >is genetic, since it is inherited in all environments. > >--------------- >uunet!tdatirv!sarima (Stanley Friesen) Both groups are speakers of Indo-European (i.e. languages derived from proto-Indo-Hittite). It does not follow that both groups are _descended_ (in the genetic sense) from a single proto-population. Skin pigment may be heritable, but language is not. One of the wonderful things about human beings is that they can _learn_ languages other than the one their parents spoke!!!! I know of no evidence that the speakers of Sanskrit-derived languages in northern India are more genetically related to Scandanavians than they are to the speakers of Dravidian languages (non-Indo-European) in southern India. I actually heard an interview with Michael Jordan on TV recently. It was conducted in English! Since since that means his ancestors "must" have come from England originally, Michael's dark pigmentation "must" have been a result of _amazingly_ speedy evolution between the time of the Mayflower and today. [;-)] Ron Amundson
sarima@tdatirv.UUCP (Stanley Friesen) (01/29/91)
In article <6747@harrier.ukc.ac.uk> sss3@ukc.ac.uk (S.S.Sturrock) writes: >In article <104@tdatirv.UUCP> sarima@tdatirv.UUCP (Stanley Friesen) writes: >>This form was essentially an semi-terrestrial, bipedal >>ape, not very different from a modern chimpanzee. > >Umm, the modern Chimanzee is just as evolved as we are, see later, >Australopithicus probably shared a common ancestor with Pan I suppose. >Semi-terrestrial? Like a lungfish perhaps :-) Did I ever say otherwise. I was only saying that A. afarensis probably *looked* very much like the chimp (particularly the pigmy chimpanzee). I was *not* trying to claim common ancestry. I was claiming, and still calim, that A. afarensis had not evolved very far from that common ancestor, and that in most respect the chimpanzee has remained conservative. (The main change in the chimp appears to be the development of knuckle-walking, and probably a shift in coat color.) And yes the latest evidence strongly indicates that A. afarensis was only partially terrestrial. It had a pelvis and hind leg adapted for walking upright, but it also had the long curved fingers, long toes and shoulder structure of a brachiating ape. [In fact it shares more features with brachiating apes than with modern humans, so by raw character count it would seem to have been almost purely arboreal.] Or did you think I meant semi-aquatic? I was contrasting 'terrestrial' with 'arboreal'. [Maybe I have been reading too many papers by primatologists, who routinely make this contrast in this way - (e.g. a Baboon is terrestrial, a Guenon is arboreal)]. >>No it is not. Evolution (in the biological sense) implies *genetic* change. > >Did I mention genetic change? Nope, doesn't mean it is not evolution. >As I see it, evolution is a response to an environmental change, so, are >you saying that a better diet is not environmental? This may be your definition, but it is *not* the one used by trained biologists. We restrict the term evolution to alteration due to genetic differences. Thus, as long as you use your own private definition of evolution when talking to biologists you will get this sort of misunderstanding. > The capacity to be >tall may have been around for a long time but it was not expressed, it is >now. Depends on what you consider to be evolution, for instance two >groups of organisms might be identical genetically (at least within their >gene pool) but have behavior differences which mean they will never cross >breed, is that evolution? If we start getting bogged down in just the >genetic change scenario we may be simplifying the situation too far. No it is not evolution, it is an environmental barrier to breeding, that may, with time, lead to the gradual evolution of intrinsic breeding barriers. Only if the behavioral differences have a genetic basis would a biologist claim that evolution had occurred. Note that externally imposed differences in behavior or form may ultimately become incorporated into genetic changes. So such a situation is often the source of the selective pressure that causes evolution (in the biological sense). >Maybe my view of evolution is not strictly the Biological one, but since >I trained as a Palaeontologist and had to deal with very dead organisms >I didn't get much chance to study the genetics of evolution. This is >of course an old argument between Biologists and Geologists/Palaeontologists. >In terms of fossils, any change in a species *has* to be put down to evolution >because we don't have any other answer close at hand. Change in size >of organism within a population is most definately important. Hmm, I think this is changing. Certainly paleontologists are paying more attention to population biology issues. Also, I believe that purely environmentally driven changes are not sufficiently stable to show up in the fossil record. The difference in time between 1200 and 2000 AD would be totally unresolvable in the geological column. Thus a paleontological sample of modern Homo sapiens would end up lumping all late Holocene people into one bucket. No temporal trend would be visible at all. [Indeed, if our civilization disintegrates the nutritional levels will revert to the old values, and small sizes will again prevail, all within a geologically instantaneous time.] [I.e. if you can see a directional change in the fossil record, it almost has to be genetic to have lasted long enough to see]. In fact it is this instability of non-genetic change that has lead biologists to restrict the term evolution to genetic change. >... It can be seen in the fossil >record that species may experience long periods in which no external >change in appearance has occured. But this does not mean evolution has >stopped, the capacity for >a change can continue to happen without being expressed, then when the >environmental pressure changes the organism can adjust quickly, as is also >seen in the fossil record. Who is right? I have never seen any convincing evidence for this style of genetic change. [And a change in 'capacity' must necessarily be genetic]. That is, except for random genetic drift, genetic differences must be expressed to be preserved by evolution. And there is no reson to expect that random changes will lead to any particular change in an organisms fundamental cpacities for expressing various traits. > I don't know, biologists have a >great deal of soft tissue to play with, but palaeontologists have a broard >timescale. Maybe we should go back to cladistics! :-) Gads, I hope not! I am getting sick enough of the cladistic assumptions in the research papers on dinosaurs! By the way, my main area of biological interest is paleontological. My two specialites (right now) are dinosaurs and advanced primates. [But I am having trouble keeping up on primates, since the primate paleontologists are not publishing as many symposia as the dinosaur ones, and I am too busy writing computer programs to do a proper literature search] -- --------------- uunet!tdatirv!sarima (Stanley Friesen)
sss3@ukc.ac.uk (S.S.Sturrock) (01/29/91)
In article <106@tdatirv.UUCP> sarima@tdatirv.UUCP (Stanley Friesen) writes: > >Did I ever say otherwise. I was only saying that A. afarensis probably >*looked* very much like the chimp (particularly the pigmy chimpanzee). >I was *not* trying to claim common ancestry. I was claiming, and still [stuff deleted] > Re mention of Cladistics: > >Gads, I hope not! I am getting sick enough of the cladistic assumptions >in the research papers on dinosaurs! >By the way, my main area of biological interest is paleontological. My >two specialites (right now) are dinosaurs and advanced primates. Well, at least we agree on something :-) By the way, I assume you realise that it has long been accepted that Australopithicines are not our ancestors. They may have shared a common ancestor with us (and perhaps the chimp) but are not on the direct evolutionary line that led to Homo sapiens sapiens. Oh well. Primate evolution is a rather difficult subject due to the sparse fossil record, man does not die in very good places! Dinosaurs too? Well, there we share a common interest, I can't believe that they can possibly be applying cladistics to their evolution, eek, what more can I say, Ha Ha Ha Ha!!!!!!!! maybe! Toodle Pip, Shane Sturrock, Biol Lab. Canterbury, Great Britain.
sarima@tdatirv.UUCP (Stanley Friesen) (01/30/91)
In article <6763@harrier.ukc.ac.uk> sss3@ukc.ac.uk (S.S.Sturrock) writes: >By the way, I assume you realise that it has long been accepted that >Australopithicines are not our ancestors. They may have shared a common >ancestor with us (and perhaps the chimp) but are not on the direct >evolutionary line that led to Homo sapiens sapiens. Oh well. Yeah, long accepted by cladists! I find the reasoning behind this unconvincing. Also, 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. (I.e. at least as close to our ancestry as the pygmy chimp is to the common chimp). So if you place A. afarensis in Australopithecus you are admitting that an Australopithecus is our ancestor. (Mind you I have read one paper by a cladist that removed A. afarensis from Australopithecus and placed it in a seperate taxon, called a Plesion - because putting it in A. made that genus paraphyletic). 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). >Dinosaurs too? Well, there we share a common interest, I can't believe >that they can possibly be applying cladistics to their evolution, eek, >what more can I say, Ha Ha Ha Ha!!!!!!!! maybe! Well, they are. The two latest symposia are 'The Dinosauria' and 'Dinosaur Systematics: Perspectives and ??' (oh foo I forget the exact title). [Oops, or is that 'Dinosaur Taxonomy: perspectives & ??'] They are *both* almost purely cladistic in approach. (They are also both quite excellent, if you can ignore the cladism). And Drs Bakker and Horner, two of the leading dinosaur experts alive, are both radical cladists (especially Dr Bakker, who is also a splitter). [It's too bad that 'The Dinosauria' costs $80]. -- --------------- uunet!tdatirv!sarima (Stanley Friesen)
helmuthn@bcstec.boeing.com (Helmuth Naumer) (01/30/91)
In article <6763@harrier.ukc.ac.uk> sss3@ukc.ac.uk (S.S.Sturrock) writes: >In article <106@tdatirv.UUCP> sarima@tdatirv.UUCP (Stanley Friesen) writes: >Australopithicines are not our ancestors. They may have shared a common >ancestor with us (and perhaps the chimp) but are not on the direct ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Some accept this Ho. Helmuth -- |----------| Helmuth Naumer (206) 544-9641 | HKN | BCS; P.O. Box 24346, M/S 2H-09; Seattle, WA 98124-0346 |----------| helmuthn@dsp35001.boeing.com or helmuthn@bcstec.boeing.com |||||||||||| uunet!bcstec!dsp35001!helmuthn or uunet!bcstec!helmuthn
jespah@milton.u.washington.edu (Kathleen Hunt) (01/30/91)
From: sss3@ukc.ac.uk (S.S.Sturrock) *>(me, KH) *>Sorry, evolution *must* include genetic change. This is the biological *>definition. You can discuss environmentally-caused variation if you like, *>but please don't call it "evolution" or we will all get confused. * *The Biological definition may be incorrect. I am really puzzled by what you mean by this. Evolution is primarily a biological theory. The biological definition *is* the definition of evolution. Perhaps more to the point, the biological definition makes sense -- environmentally-caused variation cannot be passed on to one's offspring, and thus cannot result in a permanent change in the population. *I find it highly amusing that Cladistics could be considered as being alive *and kicking. Maybe I am wrong but it relies on shared features to define *a similarity between species ie wings, therefore birds are closely related *to insects, and bats?!!? :-) * *Maybe you can give me a little fresh data. I believe you are confusing cladistics with pheneticism. Cladists attempt to built a classification based *only* on evolutionary relationships. Cladists love monophyletic groups, and an "animals with wings" group such as you describe would drive cladists into a screaming rage. Pheneticism was the "previous revolution" in systematics -- it was the hot controversy in the 60's, before cladistics came along. Pheneticists tried to construct classification schemes from a purely operational point of view. They group organisms solely on the basis of similarity, not by evolutionary history. The "animals with wings" group is a crude example of the kind of thing pheneticists have in mind, but their methods are more sophisticated than that -- they would be sure to notice that bats are similar in many ways to mammals, and that birds share similarities with dinosaurs. I believe the pheneticists' point was that they wanted to construct a classification *independent* of evolution, so that they can then look at their classification scheme and use it as evidence for or against certain theories of evolution. Of course, pheneticists don't always call themselves pheneticists, and cladists are often now called "phylogenetic systematists", so the terminology can get confusing. Just so you know who I'm talking about, the cladists would include such people as Hennig, Platnick, Nelson, Wiley, and Cracraft, and the pheneticists are people like Sokal, Sneath, and Rolff. Finally, there is the older group of systematists, the "evolutionary systematists". That's people like Mayr and Simpson, who use evolutionary relationships to construct classifications, but also allow morphologically different groups to be split off from a monophyletic group (like the birds being given their own class, instead of staying with the dinosaurs). To put in some historical perspective, the evolutionary systematists are the older group, and their classification schemes are the ones most of us are familiar with. Then the pheneticists (classification by similarity) came along in the 1960's and fought with the evol. syst. people. Then, the cladists (classification by evolutionary relationships) came along in the 1970's and fought a series of incredibly nasty arguments with everyone else -- what one of my professors calls "the most violent exchanges in biology and maybe in all of science." (Flame wars, basically.) The dust has sort of settled now, and from what I gather, cladistics (now called "phylogenetic systematism", remember) has ended up on top. However, the evolutionary systematists are still around, and though the pheneticists have sort of faded, their careful, rigorous methodology provided tools that everyone uses now. Well. I really don't know much about this field -- everything I just said is stuff I am basically repeating from systematics seminars I've been to. If there is a real live systematist out there on the net, please jump in and correct any mistakes I've made! *For timescales take a look at the PHYLUM Trilobitomorpha. Species in this *phylum evolved rapidly, very rapidly in fact, and the strata that the fossils *are preserved in can often be resolved down to seasons! Tell me that isn't *a fine enough resolution. :-) That's an excellent resolution! Glad to hear it. Do you have any references for where I can find out more about this? Is this common, or is such resolution only found in certain rare strata? What sort of level of resolution is there, for example, for the horse fossils? *Anyway, there are regular instances when an organism has evolved suddenly, *again, how about the Ammonoidea? I am quite clear about timescales involved, *what about the horse, there are NO inbetween fossils, just individual, *identifiable species. This is the crux of the matter, it is simple to argue *that they have stopped evolving, but to then say that 'overnight' they changed *to a new species and left no record? No I am not a creationist, or a Christian *or any other religion. * *I would like you insights, or any others for that matter. I think one big point here is that when an organism appears in the fossil record suddenly, it does not follow that it evolved suddenly. Speciation appears to take place most often among small, isolated populations, and such a new species may then re-invade the home of its ancestral "mother" species, prove itself to be fitter, and outcompete the "mother" species. Throughout most of the range of the mother species, the fossil record would record a very abrupt transition -- the "mother" species would be very abundant, and then the "daughter" species would appear all of a sudden, apparently out of nowhere. The only place that the fossil record would record the actual evolution of the daughter species is in the small area where the isolated population was that gave rise to the daughter species. If you want a more complete description of this phenomenon, check out "The Blind Watchmaker" by Richard Dawkins. This is not the only way speciation can occur, but it is probably a common way (according to current theory, that is...). The key is that the actual speciation event tends to take place in a small area. I am *not* an expert in this field, by the way, and would be happy to hear other people's opinions on this subjects. (I am primarily an organismal biologist -- endocrinology, behavior, all that stuff.) Kathleen jespah@milton.u.washington.edu
gerry@zds-ux.UUCP (Gerry Gleason) (02/14/91)
In article <106@tdatirv.UUCP> sarima@tdatirv.UUCP (Stanley Friesen) writes: >In article <6747@harrier.ukc.ac.uk> sss3@ukc.ac.uk (S.S.Sturrock) writes: >> The capacity to be >>tall may have been around for a long time but it was not expressed, it is >>now. Depends on what you consider to be evolution, for instance two >>groups of organisms might be identical genetically (at least within their >>gene pool) but have behavior differences which mean they will never cross >>breed, is that evolution? If we start getting bogged down in just the >>genetic change scenario we may be simplifying the situation too far. >No it is not evolution, it is an environmental barrier to breeding, that >may, with time, lead to the gradual evolution of intrinsic breeding barriers. >Only if the behavioral differences have a genetic basis would a biologist >claim that evolution had occurred. This discussion prompted me to speculate about just how the evolutionary pressures sort out on this issue. I would think that the average height previous to the recent change would have been in some sense optimal, and probably hadn't changed much for a while. Doesn't this mean that there is the possibility that there is now an evolutionary pressure toward being shorter? I know it would depend on the nature of the pressure and whether it is still operating. Say that being 4 inches taller increases your risk for heart attack or other conditions. Wouldn't the actually taller population be selected back toward the "optimum"? Then if the behavioral conditions are removed the population would immediately become shorter than it originally was. Gerry Gleason
sarima@tdatirv.UUCP (Stanley Friesen) (02/15/91)
In article <545@zds-ux.UUCP> gerry@zds-ux.UUCP (Gerry Gleason) writes: >This discussion prompted me to speculate about just how the evolutionary >pressures sort out on this issue. I would think that the average height >previous to the recent change would have been in some sense optimal, and >probably hadn't changed much for a while. Doesn't this mean that there >is the possibility that there is now an evolutionary pressure toward being >shorter? I know it would depend on the nature of the pressure and whether >it is still operating. Say that being 4 inches taller increases your risk >for heart attack or other conditions. Wouldn't the actually taller population >be selected back toward the "optimum"? Then if the behavioral conditions >are removed the population would immediately become shorter than it originally >was. Yow!! Good question! It is certainly possible. Though I do not know how we could test it, given the (entirely appropriate) reluctance to experiment on humans. There is also another possibility. It turns out that something superficially similar to 'inheritance of acquired characteristics' does occur. Essentially, when the environment forces a particular growth form on an organism, then any genetic predisposition to that growth form is selected for. This reulsts, eventually in a race that takes the 'enforced' growth form even when it is no longer enforced. The classical example of this is plants growing on exposed headlands next to the ocean. In these environments the salt spray caused erect, exposed branches to be killed, resulting in a low-growing, matted growth form. This growth form shows up even in plants grwon from inland seed sources, that are clearly genetically able to grow taller. However, when a seeds from the coastal plants are grown inland, away from the salt spray, they continue to grow low and flat. [Note, I am talking about plants from the same species, for instance mule-fat here in California]. Applied to the human size situation this could mean that prior to modern diets human size was limited by the environment, and our genetics had evolved to minimize the impact of this 'forced' (dietary) size limit. In this case, we have now been released from the selection for limited size and the genetic component of our size may also be increasing (slowly). -- --------------- uunet!tdatirv!sarima (Stanley Friesen)
colby@bu-bio.bu.edu (Chris Colby) (02/19/91)
In article <545@zds-ux.UUCP> gerry@zds-ux.UUCP (Gerry Gleason) writes: >This discussion prompted me to speculate about just how the evolutionary >pressures sort out on this issue. I would think that the average height >previous to the recent change would have been in some sense optimal, and >probably hadn't changed much for a while. Why would you think that? Specifically, why would you think that height, as such, is trait? Could it not just be, as mammals, we need a certain amount of "equipment" (organs, muscles etc.) to survive and when you add it all up we end up at some height. Also why, if height is a trait, should it be optimized? What mechanism(s) would accomplish this optimization? > Doesn't this mean that there >is the possibility that there is now an evolutionary pressure toward being >shorter? I know it would depend on the nature of the pressure and whether >it is still operating. What is an evolutionary pressure? Say that being 4 inches taller increases your risk >for heart attack or other conditions. Wouldn't the actually taller population >be selected back toward the "optimum"? Then if the behavioral conditions >are removed the population would immediately become shorter than it originally >was. I don't really think height is a trait. To me it's kind of like your chin, it's not something of any use just a byproduct of how we are put togethor. (Granted severe deviations from the norm could be deleterious not only to mere survival, but also to the ability to find a mate and reproduce.) Organisms cannot be "atom- ized" into traits, each of which is optimized. Each and every trait effects each and every other trait in such a way that none can really be optimized (IMHO). It is the organism as a unit that must "work", not each trait in a vacuum. Just a few thoughts to ponder, comment on or start a flame war over 8-) >Gerry Gleason Chris Colby email: colby@bu-bio.bu.edu
jbj@frc.frc.maf.govt.nz (Brian Jones) (02/20/91)
In article <75075@bu.edu.bu.edu> colby@bu-bio.UUCP (Chris Colby) writes: [stuff deleted] >why, if height is a trait, should it be optimized? What mechanism(s) >would accomplish this optimization? > [more stuff deleted] >Chris Colby >email: colby@bu-bio.bu.edu During WWII my father, an engineer, was fighting in Burma with African troops. He noted that the African hill tribesmen (they all were - not sexist) used to easily outrun the much taller plains tribesmen in hill country, but on the flat lost badly. Something to do with the lower centre of gravity in small people, he believed. If his observation is true, and it does make sense, then surely it is an example of evolutionary pressure? Now that there is no need to run to survive the advantage of short (or long) legs is removed. B. Jones (these views have nothing to do with my employer, unless they are fishy)
ronald@uhunix1.uhcc.Hawaii.Edu (Ronald A. Amundson) (02/20/91)
In article <854@frc.frc.maf.govt.nz> jbj@frc.UUCP (Brian Jones) writes: > >During WWII my father, an engineer, was fighting in Burma with African troops. >He noted that the African hill tribesmen (they all were - not sexist) used to >easily outrun the much taller plains tribesmen in hill country, but on the flat >lost badly. Something to do with the lower centre of gravity in small people, he >believed. > >If his observation is true, and it does make sense, then surely it is an >example of evolutionary pressure? Now that there is no need to run to survive >the advantage of short (or long) legs is removed. > >B. Jones > Accepting this anecdote as evidence, it does not follow that this is "surely" an example of evolutionary pressure. One obvious and uninteresting reason is that the hill people were accustomed to running in hills, and the plains people on plains. A more interesting reason is that to show that a character difference exerts selective force on a population it is necessary to show that the difference between the two populations is _due to_ selection of the character in question. It is _not_ enough just to tell a story about how a character is advantageous in a certain environment and then conclude that since "it does make sense", the evolutionary force has been demonstrated. For something to be an "evolutionary pressure" it must actually _operate_ on the group in question -- it's not enough just to show that it _might have_ operated. As my grandmother-in-law once said, "Maybe-chicken doesn't make soup". Ron Amundson