Image is from University of California Museum of Paleontology’s Understanding Evolution
One of the outstanding recent scandals of biology has been the notion that evolution is not progressive, a concept that flaunts the evidence of our eyes. Any reading of the fossil record shows simpler starts followed by increasing sophistication, along many lines. Even where morphology doesn’t appear to change, competition between organisms can lead to an arms race, known as the Red Queen hypothesis from the children’s book Through the Looking-Glass, and What Alice Found There: “Now, here, you see, it takes all the running you can do, to keep in the same place”. Overall, there is indeed an increase in biodiversity over evolutionary time which we could delibately maintain. To be sure, there is some apparent backsliding, as when an independent organism, even a bacterium, becomes a parasite, or parts become vestigial or discarded, or features disappear and recur in closely related species, or a comet or an asteroid wipes out 95% of living species. But on the whole, some species in each branch of the tree of life tend to march on with richer diversity of structure and perhaps behavior. One caveat is that the total number of species, though perhaps not their complexity, may have peaked 530 million years ago, due to subsequent extinctions.
Those that stay behind may not progress, or at least not appear to do so in morphology. The most blatant example of the latter is that we are descended from bacteria, yet there are still plenty of our brethren bacteria around. And while we can’t be sure yet that modern bacteria are any more complex than the earliest ones, it is clear that the number of niches they live in has increased, and the corresponding biochemical and genetic diversity amongst bacteria has evolved. The diversity of minerals has increased with the evolution of life, so for example we can expect a parallel increase in the number of environments on minerals for bacteria, let alone environments in and on other organisms, in the evolution of bacterial film communities, symbioses and communities on and in eucaryotes that have been called symbiocosms. The heterogeneity and geographic separation of places that bacteria can live contributes to their diversity, and many have been classified as extremophiles or polyextremophiles for the extreme environments they live in. Therefore progress may be occurring at every level.
Some work on progressive evolution has been couched in the language of “increase in complexity”, and thus centers around the construction of measures of complexity and empirical data on whether complexity is increasing. For example, John Tyler Bonner counted the number of cell types in an organism as a measure of complexity. In our work, because of the direct link between the number of cell types and the number of differentiation waves, this count is clearly a measure of both differentiation and morphogenesis, i.e., it operates at widely different size scales. On the other hand, the differentiation tree is not a linear, but rather a branched structure, so it is not subject to simple, scalar measures of complexity. The problem of estimating the complexity of differentiation trees in a way that allows comparison is a subset of the problem of complexity of networks, which is under active investigation. Insofar as the differentiation tree is the genetic program of the organism, a bifurcating alternation of molecular events and physics (differentiation waves), it may be possible to calculate its algorithmic complexity, defined as the length of the shortest computer program that successfully mimics embryogenesis.
“Progress” became a dirty word in biology because it smacks of “purpose”, and the implication that the purpose of evolution was to produce us. The concept suggests that evolution indeed has a direction, which to many religious people (including many scientists), means “God did it”. Thus, for a biologist to speak of progress is said to play into the hands of the creationists and the Intellegent Designers (who distinguish themselves from other creationists by not uttering the word “God”). Rather than take this head in the sands approach, we will confront progress in evolution in this chapter.
On the question of the centuries old debate of the relationship between science and religion, we stand firmly in the belief that the universe is one, deserving one unified explanation that works, and do not opt for the so-called “Nonoverlapping magisteria” or “…lack of conflict between science and religion due to the lack of overlap between their respective domains” . That is an imaginary line in the sand. Attempts to draw it, or to claim the whole territory, from either side, are failing. Rather than propose a God of the gaps or science of the gaps, we prefer to push our investigations as far as we can with testable hypotheses, and leave the gaps of both kinds for later generations to work on.
Our plan in this chapter is, then, to delve into the evolutionary consequences of differentiation waves, ending with a plausible demonstration that they may be responsible for progress in evolution.
Introduction to Chapter 11, Why Evolution is Progressive, in Embyrogenesis Explained.