werner@aecom.UUCP (Craig Werner) (12/17/86)
It has often been argued that biological change (evolution, I daresay)
can occur even in the absence of environmental change. To some this has
been used to discredit the entire evolutionary scenario. However, it
was proposed (and I wish I know by whom) that interspecies competition may
play a more important role than previously assumed. They dubbed this
theory "The Red Queen Hypothesis", after the Red Queen's advice to Alice
in "Through the Looking Glass":
"Sometimes you have to run as fast as you possibly can just to
stay in the same place."
This (in my mind) has got to be the best-named theory in science.
And it also echoes the prefacery remarks in (again I don't remember which
text): this book is not designed to be an introductory text. The best
introductory text on this subject is Alice in Wonderland, but then again,
that goes for most subjects.
--
Craig Werner (MD/PhD '91)
!philabs!aecom!werner
(1935-14E Eastchester Rd., Bronx NY 10461, 212-931-2517)
"I tell you I'm a thief and you call me a liar?"gallagher@husc4.harvard.edu (paul gallagher) (12/19/86)
In article <741@aecom.UUCP> werner@aecom.UUCP (Craig Werner) writes: > > It has often been argued that biological change (evolution, I daresay) >can occur even in the absence of environmental change. To some this has >been used to discredit the entire evolutionary scenario. However, it >was proposed (and I wish I know by whom) that interspecies competition may >play a more important role than previously assumed. They dubbed this >theory "The Red Queen Hypothesis", after the Red Queen's advice to Alice >in "Through the Looking Glass": > "Sometimes you have to run as fast as you possibly can just to >stay in the same place." > In the past (till the 1930's) many people believed in "internal" forces directing evolution, with selection merely working to weed out the unfit. These ideas are pretty much completely discredited. Going to the opposite extreme, the New Synthesis in the 1950's rather dogmatically asserted that almost all evolutionary change was directed by adaptations to the environment. Nowadays, people have begun to realize that evolution is controlled not only by adaptations to the environment, but also by the constraints of development, history, and body architecture - and also perhaps by chance. Much allelic substitution occurs without controlling influence from selection, and with no direct relaionship to adaptation. An excellent source dealing with the profound changes occuring in evolutionary theory - which far from discrediting it, improve its ability to explain the history of life - is Stephen J. Gould's "Is a new and general theory of evolution emerging" in Paleobiology, 6(1), 1980, pp. 119-130.
gallagher@husc4.harvard.edu (paul gallagher) (12/20/86)
In article <741@aecom.UUCP> werner@aecom.UUCP (Craig Werner) writes: > It has often been argued that biological change (evolution, I daresay) >can occur even in the absence of environmental change. To some this has >been used to discredit the entire evolutionary scenario. However, it >was proposed (and I wish I know by whom) that interspecies competition may >play a more important role than previously assumed. They dubbed this >theory "The Red Queen Hypothesis", after the Red Queen's advice to Alice >in "Through the Looking Glass": > "Sometimes you have to run as fast as you possibly can just to >stay in the same place." I think this refers to "character displacement". When the ranges of two similar species overlap, one may outcompete the other and cause its elimination. Alternatively, they can develop strategies to live together in the same range. One way is spatial segregation - one species lives in one strictly localized habitat, the other lives in another so that they avoid direct competition. Another way is character displacement. Either one species comes to look very similar to the competing species, so that selection acts upon all individuals as if they were just one species, allowing the species to coexist, or the two species diverge in characters so that the two species have slightly different habitats and thus again can coexist. For example, certain closely related agnostid trilobites seem to coexist through size displacement. It was predicted that size displacement would have to be in the range of 1.28:1 in order to avoid competitive elimination. The fossils in question were investigated and did indeed show ratios in size of about 1.28:1. Also, in the small area where the ranges of the trilobites Phacops iowensis and Phacops rana overlap, P. iowensis diverged in morphology from P. rana, while P. rana converged in some characters, diverged in others. The source is Neil Eldredge, "Character displacement in evolutionary time" American Zoologist 14 (1974), 1083-97. However, Eldredge concludes that character displacement is not that important. Another way a population might change without any change in its environment is genetic drift. Any very small population has only a limited, random sample of the genetic variability within a species, and whenever two individuals reproduce, some alleles will be lost, since only one chromosome of each pair is passed down to the gametes. Thus, in a small population, there could be an evolutionary change in gene frequencies just through random chance assortment. Again, this process may not be very important. Incidently, another way evolutionary change can occur far in excess of simple responses to changes in the environment, is through changes in the timing of development. For example, neoteny: the occurence of sexual maturity in the juvenile animal. It is believed that the early fish-like ancestors of vertebrates originated when the free-swimming larvae of sea-squirts became able to reproduce, thus eliminating the characters of the adult stage. Similarly, the onset of maturity in the larvae of crustaceans may have given rise to the small planktonic copepods. Also, paedomorphosis: the retention of juvenile characters in the adult. For example, in Cambrian trilobites the visual surface of the eye was surrounded by an ocular suture - which caused the visual surface to be lossed during molting. Probably through paedomorphosis, post-Cambrian trilobites abandoned this system, replacing it with the juvenile form where the visual surface is attached directly to the inner body. In general, many people once thought that organisms were ideally adapted to their environment. So, in order to explain why they changed through time, they had to say that their environment changed and that each change in a characteristic corresponded to a perfection of its ability to function in its environment. Now, people realize that things are much more complex. Stephen J. Gould uses a metaphor originated by Galton - the organism is not a sphere which can be turned in any direction and any increment by changes in the environment. It is a polyhedron, each of whose faces is a point of equilibrium. Small environmental change will not turn the polyhedron to a new face, and a big push which succeeds in changing the face of the polyhedron may bring with it a whole set of changes not accounted for by natural selection. "Most of the changes in evolutionary viewpoint that I have advocated...fall out of Galton's metaphor: punctuational change at all levels (the flip from facet to facet, since homeostatic systems change by abrupt shifting to new equilibria); essential non-adaptation, even in major parts of the phenotype (change in an integrated organism often has effects that reverberate throughout the system); channeling of direction by constraints of history and developmental architecture. Organisms are not billiard balls, struck in deterministic fashion by the cue of natural selection, and rolling to optimal position on life's table." - (Stephen J. Gould. "Is a new and general theory of evolution emerging?" Paleobiology, 6(1), 1980, p. 129). Paul G.
jc@cdx39.UUCP (John Chambers) (12/23/86)
> >It has often been argued that biological change (evolution, I daresay) > >can occur even in the absence of environmental change. To some this has > >been used to discredit the entire evolutionary scenario. Anyone that argues that environmental changes are necessary to drive evolution is simply ignorant of the low-level mechanisms. Consider the scenario: A stray alpha particle comes zipping along, smashes through the fringes of a DNA helix, and when the electrons settle down again, a nucleotide or two have been changed. About 3 times out of each billion such occurrences, this is in a cell that produces a sperm or ovum, and the change is passed on to offspring. Furthermore, there's no problem coming up with 'constant' features of the environment that exert selective pressures. One such is called 'predators'. Even if the predators were unchanging, they would still select for avoidance capabilities in a prey species. Alpha particles and predators are part of the environment of all living creatures. [OK, a flying alpha particle isn't a feature of a 'constant' environment. But in that sense, there is no evolution in a truly constant environment, because everything is at absolute zero and there is no life.] -- John M Chambers Phone: 617/364-2000x7304 Email: ...{adelie,bu-cs,harvax,inmet,mcsbos,mit-eddie,mot[bos]}!cdx39!{jc,news,root,usenet,uucp} Smail: Codex Corporation; Mailstop C1-30; 20 Cabot Blvd; Mansfield MA 02048-1193 Clever-Saying: For job offers, call (617)484-6393 evenings and weekends.
michaelm@bcsaic.UUCP (Michael Maxwell) (01/05/87)
In article <927@husc6.UUCP> gallagher@husc4.UUCP (paul gallagher) writes: >For example, certain closely related agnostid trilobites seem to coexist >through size displacement. It was predicted that size displacement would >have to be in the range of 1.28:1 in order to avoid competitive elimination. >The fossils in question were investigated and did indeed show ratios in >size of about 1.28:1. I suppose I'm being lazy (I could look up the reference), but I gather that these species of trilobites were quite similar morphologically, and lived in quite similar (or identical) environments. Has anybody suggested that these were actually individuals of the *same* species (possibly of different sexes)? I know next to nothing about trilobites, but it certainly sounds suspicious... I seem to recall that several living `distinct' species have turned out to be members of the same species which underwent fairly radical changes during ontogeny (Parrotfishes come to mind). BTW, how easy is it to tell male and female trilobites apart? >Another way a population might change without any change in its environment >is genetic drift. Any very small population has only a limited, random >sample of the genetic variability within a species, and whenever two >individuals reproduce, some alleles will be lost, since only one chromosome >of each pair is passed down to the gametes. Thus, in a small population, >there could be an evolutionary change in gene frequencies just through random >chance assortment. >Again, this process may not be very important. I suggested this in answer to an exam question once, as the origin of blind (eyeless) cave fish. (The incidence of eyeless fish is quite high, but for obvious reasons the eyeless ones seldom make it very far in life up here.) The professor didn't like my answer...his point was that there had to be a selective advantage to blindness in cave life. I didn't believe so at the time, and I'm still skeptical. Anyone care to comment? -- Mike Maxwell Boeing Advanced Technology Center arpa: michaelm@boeing.com uucp: uw-beaver!uw-june!bcsaic!michaelm
dean@violet.berkeley.edu (Dean Pentcheff) (01/07/87)
In article <124@bcsaic.UUCP> michaelm@bcsaic.UUCP (Michael Maxwell) writes: >I suggested this [genetic drift] in answer to an exam question once, as >the origin of blind >(eyeless) cave fish. (The incidence of eyeless fish is quite high, but for >obvious reasons the eyeless ones seldom make it very far in life up here.) >The professor didn't like my answer...his point was that there had to be a >selective advantage to blindness in cave life. I didn't believe so at the >time, and I'm still skeptical. Anyone care to comment? I'm not sure, but I suspect that eyelessness in cave fish arose independently from several groups of (eye-bearing) fish. If this is the case, it seems unlikely that cave fish stemming from different ancestral groups would share the _same_ trait due to drift, given that there are only a few characters that tend to be different in cave fish (lack of eyes, lack of pigment). If, on the other hand, the trait conferred a selective advantage, then its appearance in several groups is reasonable. The advantage (presumably) has something to do with energy savings for the eyeless fish (though this is a rampantly "selectionist" argument). -Dean (dean@violet.berkeley.edu)
michaelm@bcsaic.UUCP (Michael Maxwell) (01/09/87)
In article <2103@jade.BERKELEY.EDU> dean@violet.berkeley.edu (Dean Pentcheff) writes: >In article <124@bcsaic.UUCP> michaelm@bcsaic.UUCP (Michael Maxwell) writes: >>I suggested this [genetic drift] in answer to an exam question once, as >>the origin of blind >>(eyeless) cave fish. (The incidence of eyeless fish is quite high, but for >>obvious reasons the eyeless ones seldom make it very far in life up here.) >>The professor didn't like my answer...his point was that there had to be a >>selective advantage to blindness in cave life. I didn't believe so at the >>time, and I'm still skeptical. Anyone care to comment? > >I'm not sure, but I suspect that eyelessness in cave fish arose >independently from several groups of (eye-bearing) fish. If this is >the case, it seems unlikely that cave fish stemming from different >ancestral groups would share the _same_ trait due to drift, given that >there are only a few characters that tend to be different in cave fish >(lack of eyes, lack of pigment). If, on the other hand, the trait >conferred a selective advantage, then its appearance in several groups >is reasonable. The advantage (presumably) has something to do with >energy savings for the eyeless fish (though this is a rampantly >"selectionist" argument). > >-Dean (dean@violet.berkeley.edu) This is what the prof said--there had to be a selective advantage. My feeling is that there simply couldn't be any selective DISadvantage--as there is in fact no disadvantage to blindness or lack of pigment in caves. There WOULD be a disadvantage to almost any other simple change, hence the "only" changes that show up in the distinct groups of cave fish are these two. (Improved tactile perception would be an ADvantage--but probably much more unlikely to arise in a short time frame than lack of eyes or pigment.) Oh, one other difference that has appeared in at least some groups of cave fish (I doubt whether it has been extensively tested, it may appear in others) is lack of circadian rhythms. Again, it seems that if this were lost from a couple individuals in a very small population, it might be perpetuated simply by chance (i.e. due to chance fluctuations in the population which might kill off all but their offspring). -- Mike Maxwell Boeing Advanced Technology Center arpa: michaelm@boeing.com uucp: uw-beaver!uw-june!bcsaic!michaelm
dbb@aicchi.UUCP (01/10/87)
In article <124@bcsaic.UUCP> michaelm@bcsaic.UUCP (Michael Maxwell) writes: > >I suggested this in answer to an exam question once, as the origin of blind >(eyeless) cave fish. (The incidence of eyeless fish is quite high, but for >obvious reasons the eyeless ones seldom make it very far in life up here.) >The professor didn't like my answer...his point was that there had to be a >selective advantage to blindness in cave life. I didn't believe so at the >time, and I'm still skeptical. Anyone care to comment? >-- Well... Some thoghts on this; First, it seems to me to be possible that traits arise that are simply no DISadvantage. These traits may have disadvantageous effects in a different environment, but are OK in the special environment in which they arise. Blind fish would not survive well in a sunny pond. After some number of the population is blind, we must THEN start to look for some advantage to blindness. Perhaps the production of dyes for use by the retina saps the cave fish of amino acids that are not often found in his world. If there were a small famine due to unusual surface conditions, the sighted fish might die faster than the blind ones. Repeat this pressure many times over thousands of years, and you have a totally blind fish population. It is also possible that the sighted fish have a smaller range than the blind ones. They might choose to remain in the parts of the cave where light filters in from the surface. The blind fish, with no such tropism, would be free to populate the nether regions... Any constructive thoughts on these opinions? -- -David B. (Ben) Burch Analysts International Corp. Chicago Branch (ihnp4!aicchi!dbb) "Argue for your limitations, and they are yours"