The new modern synthesis: When Charles Darwin wrote Origin of Species he made a couple of good points. One, and this was the bulk of the book when he was not talking about his pet pigeons, was that the definition of a species is arbitrary. The second was that evolution had been going on a long time.
The idea of evolution itself can be traced back to Aristotle, but Aristotle made no mention of profound changes accumulating over a long time. And of course animal breeding differs from evolution only in point of the selecting agency and length of time. Breeding has not, to date, produced such profound changes as nature. So Darwin gets credit on the point that big changes can occur over sufficient time.
However, in rejecting the idea of a species as a somehow immutable Platonic ideal transcending ordinary reality, and not offering an alternative, Darwin was left with the idea that evolution works on an individual. There was a strong political reason for this concept, which I hope to delve into one day, but it does present a problem. An individual can’t evolve. An individual can change, but that change is not automatically transmitted to the offspring normally. True, there are now epigenetic effects where a change can be transmitted, but we can hardly hold Darwin into account for not having commented on the methylation of sites on DNA. He had evidently never heard of Mendel and genes, and he at least at one point was ready to accept the idea of the inheritance of acquired characteristics. If that happened, then indeed an individual could evolve by the same mechanism that ultimately produced the rich species variation of nature.
The situation was patched up with a set of ideas called the Modern Synthesis. In this formulation of evolution genes are taken into account and the idea of a species is rehabilitated. The species becomes the unit of evolution rather than the individual. A single major mutation that produced improvement might occur, but this would be followed by a host of mutations of less impact that fine tuned the result.
While inheritance of acquired characteristics doe not fit with our model, the Modern Synthesis works quite well. The multiple fine tuning mutations are the target of what we call “detuning mutations” that essentially roll back the advances made by fine tuning and are susceptible to being removed by selection or repaired by further fortunate mutations that restore the status quo or find a new way to accomplish the same thing.
The Modern Synthesis has been the basis of work for decades. That has not always prevented quarrels. For a substantial period of time, there was less than cordial debate between the evolutionists and the geneticists.
Can you believe it? I could hardly do so when I read that it had happened. Certainly my own genetics course in college made no mention of the idea that there even could be such a conflict. But apparently there was for many years. That is now past us of course, and geneticists have for many years been embracing evolution and even using their own techniques to propose new evolutionary trees.
We now learn of a “new Modern Synthesis.” (Modernizing the Modern Synthesis, Elizabeth Pennisi SCIENCE vol 321 number 5886 July 11, 2008 page 196) The new formulation is yet to be agreed on, but it is going to take into account the acquired characteristics as defined by epigenetic effects and also (wait for it) a central roll for control systems.
Control systems must also be subject to fine tuning and fine detuning mutations, so to that extent they are singing our song. The model presented on the Main Page is so basic that it works just as well with the tuning mutations of the Modern Synthesis and the adjustment of control systems in the new Modern Synthesis and, I suppose, epigenetic effects.
But there is another opportunity for the new Modern Synthesis. I wish I could say this kindly, but a species is a myth. Darwin gets full credit on that over and against Modern Synthesis. There are many definitions of a species, but the general drift is that a species is all of the individuals of some form that are interbreeding or potentially interbreeding. It is now known that most species consist of small, mutually isolated populations. The notion of a species then is a big “maybe,” “might be” or “could be.” It isn’t real. What is real is the smaller population that is actually interbreeding.
Just because a gene or a constellation of genetic tunings might get fixed in a single population does not mean it is going to get fixed, to become universally present, throughout the population. We all knew that all along. Dogs are all one species in that they are able to interbreed, although I often wonder whether size considerations alone might put a limit on that, but they exist in different breeds. And those breeds stay separate.
Selection, then, does not apply to the “species,” nor to the individual. Selection applies to the population that is actually interbreeding.
I sometimes imagine a species widely spread through a region if you could see all the members and watch them over time to look sort of like a boiling pot of water. A single sub population grows from being very small, and then a number of things can happen. It can be wiped out by untoward events. It can be kept to restricted numbers by environmental influences so that it is in an unstable equilibrium, or it can grow to the point that it is no longer fertile enough to sustain itself. The Sibly graph in the 4th figure on the Main Page of this site demonstrates that this is by no means uncommon. Then, like a bubble reaching the surface of a boil, it simply vanishes.
As populations vanish, others are able to bud off from surrounding populations and occupy the newly vacated niche.
So that will be a challenge for the new Modern Synthsis. Somehow it must take into account not only epigenetic effects and control systems but also the now understood genetic limits on population size and base selection on real interbreeding populations not hypothetical ones.
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