What is rapid evolution in biology?

What does rapid evolution consist of, and to what extent does it occur in living beings?

Evolution, from a contemporary point of view, is an issue that has zoologists, geneticists and phylogeneticists on their toes. It is clear that planet Earth is in a period of profound change and, therefore, the rates of genotypic and phenotypic variability of species are no longer circumscribed to the theoretical parameters traditionally postulated, at least to some extent.

For example, many may not know that today, as these lines are being written, we are in the midst of the sixth mass extinction (or anthropocene extinction). The current rate of extinction is 100 to 1,000 times higher than what would be expected in a natural environment and, therefore, we are not surprised to learn that one in 8 birds, one in 4 mammals and one in 3 amphibians are in danger of extinction. Plants are not far behind, as 70% of all plants are at risk.

With these preliminary data, we want to highlight a reality: rapid evolutionary processes that respond to environmental variations could be essential for the permanence of certain taxa over time in such a changing and unstable world. If you want to know all the secrets behind this little-explored concept, read on.

What is biological evolution?

To lay the foundations of evolutionary mechanisms is the first step to adequately explore the subject that concerns us here. In simple terms, evolution can be defined as the set of changes in genetic (encompassed in the genome) and phenotypic (the expression of this genome) characters of biological populations through generations. There are two broad types of evolution: divergent and convergent.

Divergent evolution is that in which a species, over time, separates into two different species.. This type of adaptive processes is encompassed in the term "speciation", where living beings from the same population acquire different traits in the face of different challenges, whether due to physical, physiological or chromosomal barriers (among many others) until they become different species that cannot reproduce with each other.

On the other hand, a species can also appear where there used to be another, without the need for two populations to separate. Simply put, the genetic changes in a particular taxon may be sufficient for us to say that one species has evolved into another.

In convergent evolution, two different species (or more) acquire similar traits because they have been subjected to similar evolutionary pressures..... For example, the bodies of a whale and a fish have comparable features with analogous functions (swimming and underwater predation), but their evolutionary history and ancestry are completely different.

Finally, it is necessary to note that the most powerful mechanism in describing the evolution of species is natural selection, that "force" that promotes the permanence of the fittest and causes the less viable to disappear from the gene pool. However, this is not the only one: processes such as genetic drift cause the loss and variation of genes in populations, although these are random and do not respond to the biological fitness of living beings.

What do we mean by "rapid evolution"?

To include rapid evolution in the current definition of evolution is extremely complex, since it is assumed that genetic changes in animal species (not so much in viruses and bacteria) occur slowly, over thousands of years.

The term "rapid evolution" is used in scientific publications to describe changes in allelic frequencies (allele frequencies). changes in allele frequencies (gene variations) within a specific population within a few generations.. These changes within the same species can arise from the appearance of new genotypes (mutations), gene flow between populations or genetic mixtures between individuals and/or species.

Some authors postulate that rapid evolution must involve a change in the ecological trajectory of the populations that undergo it, i.e., it must be translated into a series of tangible observations that demonstrate that the living being has "changed", simplifying the language as much as possible. Meanwhile, other researchers argue that this need not necessarily be the case: sometimes, rapid evolution can occur to maintain the status quo of a population in the ecosystem in which it proliferates, without ethological changes or changes in the food chain of the population, for example.

The race of populations against extinction

The potential for local adaptation by a population (and thus its potential for rapid evolution) depends on several factors. Among them, we find the following:

• The strength of local selection, i.e., the environmental changes and challenges that the given population must face.
• The number of variable genes within the population under analysis.
• The population size, since the larger it is, the more it can cope with random processes such as genetic drift.

Thus, we see that an accelerated rate of evolution depends both on the environment and on the intrinsic characteristics of the species under analysis.. For example, if we look at a taxon that has hardly varied at all in the last 1,000 years and has extremely low genetic variability, it is hard to imagine that it could suddenly accumulate tangible genotypic changes in a few generations.

In addition to this, it is worth noting that there are regions of accelerated growth DNA (ARs) in many animal species, i.e., they undergo much faster mutation rates than expected. One could go so far as to imagine that the higher the proportion of ARs the more likely rapid evolution would be but, again, at this point we can do no more than speculate.

Darwin's finches: a textbook example

To speak of rapid evolution at present is, in many cases, to be untruthful, since even if it occurs in a narrower time window than normal evolutionary processes, it is still too wide an interval for one (or more) studies to cover..

On the other hand, there are examples that demonstrate to some extent the ideas postulated here. A clear event that shows this is that of one of Darwin's finches (inhabitant of the Galapagos Islands) that, according to a study, decreased the average size of its beak in 22 years due to the introduction of another competing species.

It turns out that finches with larger beaks were introduced into its habitat and thus displaced the original large-billed finches by being more effective at destroying hard seeds. Thus, smaller beaked birds that exploited a niche (the smaller seeds) where they did not (the smaller seeds) where there were no competitors. For this reason, the proportion of individuals in the original population with small beaks gradually increased.

Final considerations

Do not believe everything you see in certain media. Arguing the presence of a rapid evolutionary process is extremely complex, as it does not happen in one or two generations. There are many, many factors to be taken into account and, therefore, we ask you the following questions: did the favored trait in the population already exist before the supposed "rapid evolution"? Has it been fixed over time or is it a sporadic observation? Is the variation significant?

For example, some media argue that certain species have "learned" to metabolize the venom of a species introduced into their habitat within a few years. Fascinating, isn't it? We dare say that this is practically impossible. It is one thing if there are mutations in a population that alter the composition of a toxin and the individuals that present it are favored, and quite another if this character appears out of nowhere as a response to a given selective pressure. in response to a given selective pressure. If rapid evolution were so simple and efficient, how is it that almost 150 species become extinct every 24 hours?

Summary

In these last lines we have not intended, far from it, to dismiss the concept of rapid evolution. What is necessary is a critical and analytical perspective. Evolution, in all cases, is a slow process that requires a fixation of traits over time.. Simply put, we cannot know whether a population trend is sporadic or definitive until many, many years after its documentation and, therefore, demonstrating rapid evolution in complex beings is a real headache.

Bibliographical references:

• Ferris, E., Abegglen, L. M., Schiffman, J. D., & Gregg, C. (2018). Accelerated evolution in distinctive species reveals candidate elements for clinically relevant traits, including mutation and Cancer resistance. Cell reports, 22(10), 2742-2755.
• Maron, J. L., Vilà, M., Bommarco, R., Elmendorf, S., & Beardsley, P. (2004). Rapid evolution of an invasive plant. Ecological Monographs, 74(2), 261-280.
• Thompson, J. N. (1998). Rapid evolution as an ecological process. Trends in ecology & evolution, 13(8), 329-332.
• Yoshida, T., Jones, L. E., Ellner, S. P., Fussmann, G. F., & Hairston, N. G. (2003). Rapid evolution drives ecological dynamics in a predator–prey system. Nature, 424(6946), 303-306.