The Macroevolution Scam
The following article was first posted in the newsgroup, talk.origins. In a sense it is a scam in its own right - that is, it makes observations that are correct (in so far as they go) but makes them in inflamatory language that invites indignant and erroneous responses. It succeeded quite well in that ignoble objective.
There is a scam, quite commonly used by talk.origins regulars, which centers on the term "macroevolution". There are several variations of this scam. The simplest variant involves equivocation between two senses of the word, "macroevolution".
One definition is "evolutionary changes at the level of species and above". Another is "major structural changes in species". The scam consists of pointing at minor species differentiation observed in the present and saying we have observed macroevolution. Now it is certainly true that we have observed speciation occurring and speciation is macroevolution according to the first definition. But it does not follow at all that the sort of speciation that is observed is equivalent to major structural changes.
Consider some typical examples of observed speciation, ones often pointed at by talk.origins regulars. There is the amoebae and a parasitic bacterium that managed to set up shop as obligate symbiotes. There are some laboratory fruit flies that can no longer interbreed with wild fruit flies. There are some mosquitoes in the London underground that have adapted to life in tubeland and no longer interbreed with their cousins above ground. Instances can be multiplied.
Now consider some examples of major functional changes. Birds will do nicely. The evolution of flight in birds (under the assumption that the origin of birds is an evolutionary event) is problematic in the extreme. The ability of birds to fly requires an extraordinary number of modifications of the vertebrate (and archosaur) body structure. This is not just a question of "half a wing". Rather it requires (a) major modification of the forelegs, (b) the evolution not only of feathers (commonly excused on the grounds of insulation) but of specially formed flight feathers, (c) modifications of bones to lighten them, (d) changes in the brain to handle the mechanics of flight, (e) development of the breastbone to anchor flight muscles, et cetera. Many of these changes would have had to have been concurrently.
It should be clear that the sorts of changes involved in making a transition from a primitive archosaur to a bird are different both in magnitude and kind from those involved in the small changes that separate two populations of fruit flies that can no longer interbreed. It quite illegitimate to point to the speciation of fruit flies as macroevolution as though it accounted for the evolution of birds.
Once the equivocation scam has been penetrated (and it is not hard to recognize that it is a scam) there remains the problem of accounting for major evolutionary changes.
A common tactic is to argue that many small changes will necessarily accumulate into large changes. This argument is good for a horselaugh from mathematicians. Many small changes may accumulate into large changes but it is not at all inevitable. Persons not convinced may sum terms of the series sum(1/2**n), n=0,1,... and report back when the sum exceeds 3. When they have given up on that they can graduate to the study of random walks in basins of attraction.
Evolutionary theory does not depend upon any thing so crude. The Darwinian thesis runs much as follows: In the heritable elements of members of populations there are variations (mutations). Those members of the population which have favorable variations are more likely to survive and pass those favorable variations on to their offspring (natural selection). It would seem to follow that over time the fitness of populations would continually increase.
This argument, in its raw form, is an illusion. What happens is that as the population becomes fitter is that the ratio of favorable to unfavorable variations declines because the possible improvements are, so to speak, used up. Evolutionary change via natural selection can only occur if fitness (i.e., the meaning of favorable variation) is continually being changed.
The difficulty with the Darwinian thesis is that it doesn't very well account for functional change. Thus the archosaur (currently an dinosaur) that is supposed to have evolved into a bird had to acquire some how a series of modifications that suit it for flight. The standard tactic here is to invoke exaption, i.e., to claim that a feature already of use turns out to have a different use which may be improved in turn. It is here that major moves into the fairy tale land of "just so" stories are popular.
Consider again those pesky birds. Some dinosaurs - so we are told and current finds suggest that it might well have been - had feathers of sorts. This in nowise establishes that these putative feathers were at all usable or relevant for flight. Ratites have feathers which are quite good for insulation and utterly useless for flight. We then are told various tales. One tale has it that there were tree dwelling dinosaurs who took up gliding. Another has it that feathered arm motions in ground dwelling dinosaurs aided them to move more quickly. It is not necessary in these stories to embellish them with substance. Thus it is not necessary to whether there were genetic changes that could have transformed insulation feathers into flight feathers. It suffices that birds have flight feathers so the change must have happened. That there are significant differences between the mechanics of gliding and powered flight can be glossed away. Likewise it is not necessary to present evidence that there ever were any tree dwelling dinosaurs. And so on and so forth.
The Darwinian thesis depends upon a concealed premise, namely that of a relatively unlimited plasticity of inheritance. In Darwin's day this was a reasonable assumption - very little was known about the mechanisms of inheritance. In the early days of the Modern Synthesis of Mendelian inheritance and Darwinian Natural Selection it was rather blithely assumed that inheritance was "soft" because there was large numbers of genes - millions of them. This turns out not to be the case - there are only a few tens of thousands in vertebrates. Moreover the number of genes that specify the body plan, the homeobox genes, are much smaller in number. There is not an unlimited plasticity of inheritance. This should have always been obvious; vertebrates, after all, are all built upon a basic body plan with variations on a theme. The consequence is that the scope for significant variations in body morphology are limited; it is not at all clear that the supposed chains of adaptive change correspond to anything real.
In short we have on one hand the observation of relatively minor changes in extant species and the other hand fossil remains of diverse species that have lived in the past. The two are connected by inordinate handwaving.
Some of my favorite remarks among the responses:
Eros: [badly thought out stuff deleted]
Afterthoughts about responses
Many of the responses centered around objections to the remarks about macroevolution being the cumulation of small changes. This is a subject in which many people go astray. There is no significant doubt that the genomes of the species of life change change steadily over time in small steps. Yet evolution in the large is not simply a matter of the acumulation of small changes. Observation of extant species shows us that species fluctuate rapidly (on geologic times scales) in their characteristics. Paleontological observations show us that species tend to be stable over long periods of time. The pace of the evolution of the genotype is only loosely coupled with the pace of the evolution of the phenotype.
Another area of reponses were objections to the remarks about "just so" stories. Here, most respondents tended not to recognize how tentative and incomplete adaptive hypotheses are. The fundamental difficulty is that we simply don't know all of the relevant factors and how important they are.
A few respondents, Chris Nedin in particular, pointed out with references that the evolution of birds is not quite as problematic as I painted it.
This page was last updated April 5, 2001.