Punctuated equilibria makes a case for shifting from microevolution & macroevolution, to ‘small evolution’ & ‘large evolution.’
Microevolution & macroevolution vs small evolution & large evolution: the Archaeopteryx represents more than accumulated gradual changes.
I am pre-publishing this sequence of essays here and in social media to elicit comments and other feedback. They will form the framework for my next book, Darwin, Dada, Dalí, Duke, & Devadevàya. Please feel free to comment below, or contact me.
Television? The word is half Latin and half Greek. No good can come of it.”
—C. P. Scott
The Re-Extended Evolutionary Synthesis
In the last post, I noted that the New Synthesis and the Extended Evolutionary Synthesis have been critical for advancing biology. Both have produced important research explaining how genes spread, and how natural selection chooses among variations of a gene (a.k.a. alleles). But as we also noted, the theory of Punctuated Equilibria suggests that we need to extend our approaches to consider where a completely new gene—a new allele, or neollele—comes from.
Punctuated Equilibria is the evidence in the geologic strata that counters Darwin’s constant gradualism. Darwin described evolution as a continuous series of constant improvements, of non-stop small advances in each species, with ‘survival of the fittest’ promoting the best advantages. The problem is, there is very little evidence for gradualism. The fossil record shows that overwhelmingly, there is not much evolution in a species for millions, sometimes hundreds of millions of years. Then a new species suddenly appears in the fossil strata. Usually it is easy to identify the originating species from which the new species branched, but there is very rarely an intermediate fossil between the two.
Speciation & Fossilization
The lack of intermediates is a compound problem between speciation, and fossilization. There are at least three reasons that speciation would be hard to find. The first is that our current theories suggest that speciation happens within relatively small groups, which means there won’t be all that many intermediates produced. Second, and from that, speciation happens within a relatively small area, which will make those places very hard to locate. Third, we believe that speciation happens very, very fast, probably in the range of tens of thousands of years. (That may not sound fast to the layman. For biologists, it’s lightning, particularly since it took millions of years for a speciation event to start.)
As for fossilization, that is also very rare: an exquisitely small fraction of living things are turned into fossils. In addition, and similar to the problem for speciation, fossilization also happens in a few, limited places (particularly for land-dwelling organisms). The result is two extremely rare processes, speciation and fossilization, which are both tightly constrained. If all of the various rare factors of speciation and fossilization don’t intersect precisely, we won’t find evidence of of evolution.
The Discontinuities of Punctuated Equilibria
We previously noted that Punctuated Equilibria present us with three discontinuities: the discontinuity of the geologic record; the biological discontinuity of a sudden appearance of a new species; and an attendant increase in diversity (which creates shifts and discontinuities in the ecosystem around the new species). I propose that there is another discontinuity, an intellectual and theoretical discontinuity, where we suddenly need the older tools from the New Synthesis to address very new problems.
Microevolution & Macroevolution
Which brings up the current terms microevolution and macroevolution. First, as the opening complaint suggests, the words are half Latin, half Greek. But sometimes biologists do that with taxonomic names. So the complaint is really more snarky than damning.
Conceptually, however, microevolution and macroevolution raise some obstacles. One is that the definitions have changed through the years, and even today continue to exhibit inconsistencies. The term ‘microevolution’ first appeared by itself; Robert Leavitt used it to describe embryologic development, which would appear to be a variation of Haeckel’s law, that the development of the embryo tends to pass through the evolutionary stages of the species. Humans, for instance, pass through pre-birth stages where we have a tail, gill arches, and even exhibit the earliest subdivision of multi-celled animals: our gut grows beginning with the anus, and then progresses to the mouth. We are ‘deuterostomes’, i.e., ‘mouth second [organisms].’ The other division, the ‘protostomes’, develop mouth-first. Humans start butt-first. Remember that the next time someone suggests you are (to Bowdlerize the common term), an ‘anal orifice.’
Returning, macroevolution was subsequently added to microevolution, but with a shift in concepts: microevolution became any change within a species, while macroevolution became change that produces new species.
There are other shifts. At one point macroevolution was employed to indicate orthogenesis, the theory that living things have an innate drive toward increasing complexity. Another problem is that some creationists have adopted microevolution to accommodate the undeniable biological changes that have happened within their proposed postdiluvian period. Finally, there is the smaller, but nevertheless important modern inconsistency in that some define microevolution as the process that happens within a breeding population, while others define it as occurring within the species. They are similar in intent, but not exactly the same thing. (I should note that I found this website which defines microevolution and macroevolution in ways that we will need here. Unfortunately, this also illustrates the current problem: the definitions have too much inconsistency.)
Large Evolution, Small Evolution
None of these are insurmountable. For our purposes here, however, the largest stumbling block is that many biologists consider the difference between microevolution and macroevolution to simply be a matter of scale. From this perspective, macroevolution is nothing more than the accumulation of many microevolutionary changes, only over a much longer time frame.
In contrast, with these essays we are trying to parse out the fundamental differences between gradualism and punctuated equilibria. So I propose to shift the concepts with different terminology. First, small evolution is the process of gradualism, those processes which we are well-documented and often artificially generated. These would include the classic insight of industrial melanism, and similar discoveries; but also, the domestication and breeding of various animals and plants. These processes are fairly well-understood, and critical for our thesis of probable changes. Meanwhile, large evolution comprises the events of punctuated equilibria, poorly-understood processes that are highly improbable: the fact that species do not change for millions of years (‘stasis’), and then quickly appear in punctuations, demonstrates just how improbable.
There are several important distinctions between these two pairings, of small evolution/gradualism, and large evolution/punctuated equilibria. One is the three related, and expanding problems we mentioned in the previous post: first, of going from no allele to a neollele; second, of accumulating enough neolleles to generate higher-level taxa; and finally, the very large problem of the LUCA, of going from innate matter to life. These are all problems that gradualism does not seem to be able to solve in any robust manner, and as such, invites new considerations, including large evolution.
Experimental Limitations
Another distinction is that our experiments are necessarily confined to small evolution. Large evolution requires biological numbers and geologic time scales, which are far beyond our current capabilities to explore experimentally. As a result, we can only analyze large evolution through speculative and theoretical approaches.
This experimental limitation, however, also offers an insight into our thinking. Because biology emerged later than the harder sciences, biologists sometimes forget that our originating problems can be larger, and therefore harder to solve, than the originating problems of the older disciplines. We have, nevertheless, inherited much of the cultural legacy of those harder sciences, and so we still place great importance on experimental proof. That prioritization understandably distracts our thinking toward our experiments, which means that we focus on small evolution. We need to reconsider these priorities in approaching large evolution.
Probability, Improbability
These distinctions reemphasize the problem of discontinuity in punctuated equilibria. Large evolution is more than accumulated gradualism, and requires a highly improbable event, or more likely, a series of improbable events. This is part of our fourth discontinuity, a statistical discontinuity, which provides us with another distinction between small evolution and large evolution. Small evolution is probable gradualism; large evolution is highly improbable punctuated equilibria.
The scientist will immediately recognize a problem in this, in that there is no clear demarcation between the two. If we had a catalog of all of the evolutionary changes that have ever occurred in the history of life, it would doubtless show a nearly-continuous curve of different probabilities. So there is no clear separation. However, neither is there a clear demarcation between microevolution and macroevolution.
Emphatic Evolution, Innovative Evolution
There is an added distinction which targets our overarching thesis: innovation. Small evolution, by and large, selects from existing genes, and shuffles and selects them. Perhaps there is a point mutation here or there, or something interesting happens with a genetic crossover at meiosis, but there is nothing radically new, nothing highly improbable. In contrast, large evolution is biological genius: it generates completely new, unexpected solutions to the 3 billion year-old problem of life.
For these reasons, I refer to small evolution as emphatic evolution, because small evolution emphasizes one gene over another, or one suite of genes over another. In contrast, large evolution is innovative evolution. Something radically new and novel — and highly improbable — suddenly appears in the fossil record.
14 Awards: The brutality of nature dominated humanity for the first 10,000 years of civilization.
Click the image for more information.
Definitions: Precision vs Accuracy
This still does not necessarily provide a neat definition and demarcation between small & large evolution, but it appears we are facing a trade-off between precision and accuracy with this problem. Clean definitions give precision, they are great for clerical sorting; but they may not be as accurate, exactly because of their tight precision. This can obstruct larger considerations.
For instance, we define species by the ability to interbreed. That definition is true, it is precise; but it is not completely accurate, in that it is not entirely complete. Indeed, the amoeba and the horse cannot interbreed. But that hardly tells us much about either of them, and it certainly doesn’t help to understand where they came from, and how they got to what, and where, they are.
The problem of defining species will become more important in upcoming posts, but for our considerations here, it is important to note that a clean definition may not always be as useful as a robust, more complete, more accurate, but more complicated understanding of the moving parts. The upside of a neat definition is that it organizes and categorizes our thinking. The downside is, it can constrain deeper analysis.
Expanding the Biologist’s Tool Box
It is said that if you are a hammer, the whole world is nothing but nails. And as we will see in future posts, our definition of a species as exclusively based on an ability to interbreed, has perhaps distracted us into believing we can build a highly evolved biosphere out of nothing but nails. The point is, some of our older tools do not readily resolve the problems of large evolution. So we would not be surprised to find that in expanding our tool box, we will have to loosen our definitions.
The problem of the definition of a species, and of microevolution and macroevolution, is an example of the yin & yang of definitions. The utility of a strong definition is that it is clearly demarcated: this is one species, that is another. Continuing from that, within a species, we have microevolution, beyond the species, we have macroevolution. That clean demarcation will sometimes limit our ability to deploy more fundamental concepts, and more fully consider the problem.
In an upcoming post, we will explore that definitional limitation more extensively. But for the moment, it is sufficient to introduce the new terms, small evolution, & large evolution.
For an ecological explanation of sexual dimorphism, click here.
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Archaeopteryx courtesy of Wikimedia.