4
$\begingroup$

I have in mind that evolution is not a constant / continuous process and that there are bursts of evolution.

Are there terms to refer to the concepts of fast vs slow evolution rates?

$\endgroup$
  • $\begingroup$ FYI, I was motivated to ask this question to address this question by @HarryWeasley in a comment. $\endgroup$ – Remi.b Oct 22 '17 at 19:05
  • $\begingroup$ Thanks a lot! It was indeed 'punctuated equilibrium' which I was referring to when I said 'bursts of evolution'! Thanks again, it's rare for someone to post a new question based on just a comment of mine!+1 for both your question and answer! :) $\endgroup$ – Harry Weasley Oct 23 '17 at 15:36
  • $\begingroup$ They talk about a cambrian explosion, but that's more an explosion of life. it's a form of genesis in unscientific terms, genesis, so it's an apex/ peak/ of species genesis. $\endgroup$ – com.prehensible Oct 24 '17 at 21:02
5
$\begingroup$

There are indeed periods of fast evolution and period of evolutionary stasis. The term "burst of evolution" is never used in the literature but below are three common terms when discussing these concepts.

First we have to realize that the term 'speed of evolution' does not mean much. We can be talking about change in phenotype through time (See Punctuated Equilibrium and Evolution and Ecology time scales) or speciation rate (See Adaptive Radiation and Mass Extinction). Also, we have to realize that we can talk about such speed of evolution on a given taxon or for the entire life on earth.

Punctuated Equilibrium

We often refer to the fact that there are periods of evolutionary stasis and periods of rapid evolution as punctuated equilibrium

Punctuated equilibrium (also called punctuated equilibria) is a theory in evolutionary biology which proposes that once species appear in the fossil record they will become stable, showing little evolutionary change for most of their geological history. This state is called stasis.

Here is a representation (from the above wikipedia link) of phenotypic divergence following an extremely gradual view of evolution and an extremely "punctuated" view of evolution

enter image description here

Evolution and Ecology time scales

Since the 2000s, there has been increased recognition that evolutionary processes even matter on a ecological/demographics scale. That is ecological/demographics processes and evolutionary dynamics influence each other dynamically and the old view that evolutionary processes are much slower than ecological/demographics processes is sometimes wrong.

See the post History: Do evolutionary and ecological processes occur at the same timescales?

Adaptive Radiation / rapid diversification

The speciation rate also varies through time. There are "burst in speciation rate" if you like the term. A sudden burst in speciation rate is called an adaptive radiation

In evolutionary biology, adaptive radiation is a process in which organisms diversify rapidly from an ancestral species into a multitude of new forms, particularly when a change in the environment makes new resources available, creates new challenges, or opens new environmental niches. Starting with a recent single ancestor, this process results in the speciation and phenotypic adaptation of an array of species exhibiting different morphological and physiological traits. An example of adaptive radiation would be the avian species of the Hawaiian honeycreepers. Via natural selection, these birds adapted rapidly and converged based on the different environments of the Hawaiian islands

You can find a list of classical examples of adaptive radiation on the above wikipedia link or at the post Is there a taxa that radiates faster?. If you don't want to be too extreme, you can as well just use the expression rapid diversification.

Mass Extinction

There are essentially two differences between an adaptive radiation and a mass extinction. 1) one is about an increase in speciation rate while the other is an increase in extinction rate. One is about a single taxon, the other one concern most of life on earth.

Because, a mass extinction sounds quite apocalyptic and because we seem to be at the start of a new mass extinction, most people are familiar with this term.

An extinction event (also known as a mass extinction or biotic crisis) is a widespread and rapid decrease in the biodiversity on Earth. Such an event is identified by a sharp change in the diversity and abundance of multicellular organisms. It occurs when the rate of extinction increases with respect to the rate of speciation. Because most diversity and biomass on Earth is microbial, and thus difficult to measure, recorded extinction events affect the easily observed, biologically complex component of the biosphere rather than the total diversity and abundance of life.

I want to highlight that when thinking of a mass extinction, many people think of a single event clearing up the surface of the earth in a day but the reality is very different. In fact, a mass extinction can well last thousands of years.

$\endgroup$
  • 1
    $\begingroup$ Great answer! Almost accepted it before I realized I hadn't posted the question! (+1)! $\endgroup$ – Harry Weasley Oct 23 '17 at 15:39
3
$\begingroup$

well to start evolution is continuous but not a constant rate. The rate is controlled by population size and the extremity of the selective pressure. Strong pressures in small populations tends to result in more rapid changes than weak pressures in large populations.

As for what to call rapid evolution it depends on what form of evolution is being seen.

  1. For instance a single large change in a single generation (often becoming a speciation event) is called saltation and is extremely rare, especially in animals, requiring a perfect storm of conditions.

  2. A founder effect induced rapid change is called a Genetic Revolution, although you will see it referred to as just a founder effect more often, and is caused by drastically decreasing the population which causes changes to spread much faster.

  3. Technically extinction might also qualify as a rapid evolutionary change.

  4. Quantum evolution is a hypothetical change in which new higher taxa arrise, but it is both poorly defined and there is absolutely no evidence it has ever occurred, indeed it appears to be mostly an artifact of how classification is determined, so I would hesitate to use it.

  5. Macromutation is the term for large single mutational changes, things like cold shock gene duplication would fall under this category. Tissue morphogenesis would be related to this, as it is a large developmental change which may or may not be the result of a large genetic change. A frame shift mutation could result in this.

  6. A rapid change in multiple species in the same place and/or time are referred to as adaptive radiation events, rapid diversification, if it is large and sudden enough it may even be referred to as explosive radiation.

Part of the issue is saying something is "fast" is a more qualitative assessment so it does not have a term in and of itself, the closest you see is things referred to as "rapid" so you might see rapid speciation or rapid extinction, rapid X or Y.

$\endgroup$
  • $\begingroup$ I think the OP is referring to geological periods where lots of different lineages arose suddenly, like the Cambrian explosion. If so, I think “rapid diversification” is exactly right. $\endgroup$ – Gaurav Oct 23 '17 at 15:17
  • $\begingroup$ A few comments. 1) Strong pressures in small populations result in more rapid changes than weak pressures in large populations is true or false depending on the details of the model and what statistic you are considering to measure speed of evolution. I would advice against using this kind of general statement. 2) I think the term 'genetic revolution' is very rarely used in the evolution literature (see e.g. this google scholar search). $\endgroup$ – Remi.b Oct 23 '17 at 17:06
  • $\begingroup$ 3) An adaptive radiation is not just [a] rapid change in multiple species. It is a sudden very high rate of speciation. 4) ` a single large change in a single generation (often becoming a speciation event) is called saltation and is extremely rate`. It depends what you mean by rare. Typically ploidy change mediated speciation and hybrid species are sudden events leading to speciation and not so uncommon in some lineages (Rieseberg et al. 2003). Otherwise, I think the answer is good. $\endgroup$ – Remi.b Oct 23 '17 at 17:06
  • $\begingroup$ Sudden is a fine qualifier I will add it. Yeah speciation kinda weird in plants to begin with, In runs back to the problems in defining species. And by rare I mean rare compared to other forms of speciation across all of life, for a general question I was trying to keep myself to a general answer. $\endgroup$ – John Oct 23 '17 at 17:14
  • $\begingroup$ @remi I'll clean it up and add some qualifiers, tell me what you think. $\endgroup$ – John Oct 23 '17 at 17:23

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.