[Note: This was sent to the Randian-Feminism list. Earlier versions of this were sent to the Extropy list and the Cornell Objectivism list. Since it received some praise, I've decided to place it here.]
This might seem a bit off topic, but on this list, evolutionary arguments have been invoked to defend or attack various positions. The typical form of these arguments has been to link some trait with natural selection via a "just so" or story scenario, expressing a qualitative and intuitive model of causation. We see this now with the penis-vagina co-evolution argument Laura Rift and others are using. Many biologists have criticized this method for being arbitrary. (For instance, B. C. Goodwin's "Evolution and the Generative Order" in Theoretical Biology: Epigenetic and Evolutionary Order from Complex Systems (1992[1989]).)
Some might argue that using a flawed method of explanation is better than using none at all. Science can work with faulty explanations. Instances of such pepper history. Bohr's model of the atom, e.g., is now known to be wrong, but it did focus attention on the important traits of atoms at that time, and hacked a path over which other thinkers could travel toward better theories.
It can also be argued that any explanation we have at any point will always be flawed. Human knowledge will never be perfect or complete. I would also agree with this and that a "just so" explanation can be a starting point for further inquiry.
Still, in evolutionary biology there are better ways of evaluation than making up a good scenario of how things came to be. They are not perfect, though they are almost all better than "just so" explanations in that they offer a testing methodology. Some of these methods have the benefit, so important in science, of being independent of particular causal theories of evolution – such as the neoDarwinian "Synthetic" Theory, the entropic "Unified Theory" (of Brooks and Wiley; see their Evolution as Entropy 2/e (1988)), and the Neutral Theory (of Motoo Kimura; see his The Neutral Theory of Molecular Evolution (1990[1983])). These methods include paleontology, population biology, phenetics, and cladisitics. Here I will concentrate on cladistics.
Cladistics uses the traits of biology groups, such as populations, species and genera, to reconstruct the lineage of the groups. The method aims at a transparent recovery of the history of cladogenic events – i.e., splits in the ancestral group. By "transparent" is meant a method that does not rely on intuitive notions, one which should allow other workers to quickly and repeatedly get the same results without bias. This is akin to addition or multiplication. If someone adds one number to another to generate a third, anyone should be able to repeat the process and clearly see how the third number is generated. (See Wiley et al. (1990) The Complete Cladist: A Primer of Phylogenetic Procedures.)
To give an example of this, Barbara A. Block et al. test the hypothesis that endothermy evolved only once in fishes in "Evolution of Endothermy in Fish: Mapping Physiological Traits on a Molecular Phylogeny" (Science (260) 1993 April 9). Endothermy is, in lay terms, warm-bloodedness. Put simply, the hypothesis is that warm-bloodedness came about once and was passed along to all other warm-blooded fishes. This would mean that all warm-blooded fishes should be more related to each other than they are to non-warm-blooded fishes – in the same way that I'm more related to my brother than I am to his wife.
Block et al. examine the distribution and changes in DNA to determine that endothermy in fact has evolved independently three times in fishes. This is the equivalent of saying that not all warm-blooded fishes are more related to each other than they are to non-warm-blooded fishes. Thus, they tested the above hypothesis and it failed. A "just so" explanation most likely would not have revealed this.
I don't have enough space here to cover the whole method, but cladistic methods work by comparing traits (which can be anything from a complex behavior to DNA sequences) between groups (e.g., species) and seeing in terms of these which groups are more closely related. This allows one to recapture the history of evolution as the sequence of branchings between traits. For instance, two species of fish which are closely related in lots of traits might differ in endothermy, giving evidence that endothermy evolved separately.
To put this a bit more clearly, imagine three sister species (species sharing a common ancestor) which form a clade (meaning there are only these species and no other that share this common ancestor): A, B, and C. Cladistically, this set can give rise to four hyptheses. The first is that they all evolved directly from their common ancestor, meaning there were no intermediary splits in their line. The evidence for this would be that none of them shared any other traits besides the ones all of them shared. Let's call their ancestor M (for mother species:). M has traits (0,0,0,0,0) – each 0 representing a binary trait: you have it or you don't have it. A has traits (1,0,0,0,0); B (0,1,0,0,0), and C (0,0,1,0,0). They all share the last two traits (the last two 0s), but differ completely in the others. Graphically this could be modeled by on point M with three lines leading to points A, B, and C.
Imagine now instead that while A, B, and C share a common ancestor, A and B share another common ancestor which C does not share. In other words, between M and A-B, there lines another species which is the mother of the A-B sister pair. We'll call this M'. Evidence for this would be something like M and C have the same traits as above, but A has traits (1,0,0,0,0) and B has traits (1,1,0,0,0). Note A and B share that first 1 with each other, but not with C; they also differ by the third 0 with C and share 0s four and five with C. Graphically, this could be pictured as a point M with one line leading to C and another leading to M' AND two lines leading from M' to A and B. Thus M evolved into M' and C, and M' then evolved into A and B. The two remaining possibilities here, which I won't cover in such detail, are that B and C are more closely related or that A and C are more closely related.
Aside from the order in which the branches happened, why would this be important? One might, say, have an evolutionary hypothesis like long billed hummingbirds in South America evolved from shorter billed ones in response to environmental pressure. I bring up this example because not only has someone done the analysis but it seems obviously to be true. In actual cladistic analysis, it was found this was not the case. The short billed ones actually came later, evolving from their longer billed cousins. If we had stuck with "just so" stories of evolution, I doubt we'd have uncovered this one. (The article in which this was covered was in an issue of BioScience about 5 years ago. I can't find it right now, but believe the whole issue was dedicated to hummingbirds. I'm sure a title search of the back issues on that keyword should arrive at it.)
Another example is that of skull size in certain fishes in Lake Victoria. Robert L. Dorit covers this in "The correlates of High Diversity in Lake Victoria Haplochromine Cichlids: A Neontological Perspective" (in Causes of Evolution: A Paleontological Perspective, edited by Robert M. Ross and Warren D. Allmon). Dorit shows particularly how one might assume skull size and shape varied gradually from one species to another in this closely related fish group. However, when molecular cladistics methods (specifically, using mtDNA to map relationships), one finds the two species with extreme skull sizes (the largest and the smallest) actually are more closely related than any of the intermediary ones. This again clearly illustrates how "just so" explanations can go wrong. (It also shows that morphological data and phenetic analyses can lead one astray.)
This is one method of testing evolutionary hypotheses. I won't cover population biology here, except to say it relies on math and has been used extensively to cover intraspecies trait changes – stuff we can see happen in the lab by running experiments. Hence the name "population" instead of "clade" or "species" – a population is considered a subset of a species. None of this means that "just so" arguments are always wrong, but a "just so" argument by itself should not be taken as a valid scientific argument. At best, it is a guess and, without further evidence to back it, must remain so. It can suggest areas for future research, but is by no means the end goal.
Also, I don't think, for instance, that Laura is off the mark regarding this particular co-evolution, but fear that she and others might use such arguments merely to try to shove her and their particular view of sexuality and gender down the rest of our throats.
I hope the above proves helpful to list members. We should aim at the truth – not presenting explanations to confirm us in our prejudices.