Yesterday I attempted to rebut Steve Jones' ridiculous contention that evolution is going to stop in the modern West. Sometimes it is difficult to really know when to start, especially when your interlocutor seems to be in "incoherent spray arguments mode." Some of the commenters also noticed the internal lack of consistency in the model which Jones was putting forward. But saying it is a model is being overly generous. In short, Jones' most solid (that is, least vague) claim is that reduction in the number new mutations being added to the population every generation is decreasing because men are having children at younger ages, on average, than in the past. Why focus on men? I noted the evidence that new mutations are about an order of magnitude more common in sperm than in ova; the reason being that sperm is produced in massive quantities through serial replication which introduces more error into the transmission process cumulatively. Of course I have to add that Jones' argument here is weak because the extant historical and anthropological does not support his contention. Part of the problem here is that Jones is good at throwing out buzzwords and sound bites. After all, most people "know" that evolution is about "survival of the fittest" and that nature is red in tooth and claw. Therefore, it naturally stands to reason that when mortality declines evolution will be a weaker force. I think the problem here is that our conception of evolution is focused too greatly on proximate modes and large scale dynamics. That is, selective high mortality rates are a "common sense" way in which the "weak" can be weeded out from the "strong." But what about the extremely high human spontaneous abortion rates? Evolutionary biologist Mark Ridley has argued that increased miscarriage rates will "balance" out the fact that more individuals with deleterious mutations are reproducing today than in the past. Selection therefore occurs in utero; we don't observe it so it is not salient to us. But it is selection nonetheless. In any case, my friend Aziz Poonawalla, a physicist by training, offered up his own model/conception of evolution. Being a physicist he was clear and formal in his exposition. I told him that the best way to think about evolution would be changes in state of the genome as a function of time. Or, more traditionally, changes in allele frequency over time. This is a "classic" definition which emerged during the early phase of theoretical population genetics. Many would quibble with it, claiming that the nature of higher order genetic architecture is critical and obscured by focusing only on proportions of alleles. I will concede that this is the the more thorough definition of biological evolution. But the changes in allele frequency definition is clear enough that I think using it as a starting point is sufficient to clarify why Steve Jones' contentions are problematic on the face of it. This is what many people think evolution is:
And they're right. But, this is an end outcome of many lower level processes. Creatures don't magically transmute into each other. I believe that part of the issue is that people conflate evolution with species phylogenies and concurrent morphological transitions. This is the extension of the evolutionary principle, but it is not the atomic unit of evolutionary theory. To understand chemistry you need to go beyond a simple periodic table. It is important to know the difference between oxygen and hydrogen, and to note character clusters of elements such as reactivity (halogens vs noble gases). But at the end of the day you need to model chemical processes as occurring via the dynamic interaction of protons, neutrons and electrons (e.g., covalent bonds), as well as atoms as units with different characteristics (e.g., ionic bonds). So on a fundamental level, this is evolution: Parent ...ATCTCTCTCGCGCAATGCGC... Child ....GTCTCTCTCGCGCAATGCGC... Note that I changed the first base pair; that's a transition. When you look at a phylogeny illustrating the tree of life with organisms of all shapes, sizes and colors, this is the ultimate process undergirding it. Once this type of process (and I want to reinforce that though I'm focusing on sequence level base pair substitutions I grant there are many other types of changes which can occur within the genome) is understood to be the root from which evolution emerges the sort of assertions Steve Jones' makes begin to lose their force, because now you can start inferring from first principles and check the "experts." On the level of the DNA sequence it is generally assumed that most evolution is neutral; that is, most of the change is due to random processes. I will avoid talking more about neutral processes to focus on selection. Not because selection is more important than neutral processes, but because I don't want to discuss something like sampling error, and I think it speaks most forcefully to Jones' common sense observation that without a great deal of pre-reproductive mortality there can be no natural selection. Consider a human population. Each individual has two copies of each gene. Let's stipulate that there is 0 mortality before the age of 50. Assume discrete generations.
