Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Path: utzoo!mnetor!seismo!husc6!husc4!gallagher From: gallagher@husc4.harvard.edu (paul gallagher) Newsgroups: sci.bio Subject: Re: The Red Queen Message-ID: <927@husc6.UUCP> Date: Sat, 20-Dec-86 01:51:51 EST Article-I.D.: husc6.927 Posted: Sat Dec 20 01:51:51 1986 Date-Received: Sat, 20-Dec-86 06:16:35 EST References: <741@aecom.UUCP> Sender: news@husc6.UUCP Reply-To: gallagher@husc4.UUCP (paul gallagher) Distribution: na Organization: Harvard Science Center Lines: 87 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.