Biology Asked on January 25, 2021
As far as I understand, various abilities like flying, sight, hearing etc. were caused by slow evolution, where those with a greater ability to to these things had better chance of survival. (If this assumption is wrong, then I am happy to delete this question).
Are there, however, any documented examples of by evolutionary leaps being made, over the course of just a few generations? I understand, that some abilities have a tipping point where one gets the ability suddenly, but there is not a lot of physiological change made. An example of this would be the ability to climb a tree, which could suddenly be possible if the body weight is reduced with just a few percent. What my question is about, are sudden changes to the characteristics of a creature.
@kmm and @shigeta provided you with a nice observational account of sudden leaps in large organisms. However, if you want to look at where this is the norm and try to build a mathematical theory then you need to look at something much smaller; the prime candidate is affinity maturation.
In the human immune system, when exposed to an antigen B cells produce antibodies. If it is your first exposure to the antigen then the antibodies produced will probably have very low binding affinity. However, after some exposure time, your B cells will start to produce antibodies with much higher affinities for the antigen and thus you will be able to better fight off the disease. The cool part, is that the antigen produced is tuned via an evolutionary process!
There is differential survival, with only antibodies with the highest affinity being able to survive. Variability is introduced by a very high mutation rate in the complementarity determing region (CDR). (Tonegawa, 1983). The length of this evolutionary process is very short, typically a local equilibrium is found after only 6-8 nucleotide changes in CDR (Crews et al., 1981; Tonegawa, 1983; Clark et al., 1985), so you need only a few point mutations to quickly develop a drastically better tuned antibody.
The standard mathematical model for this is Kauffman's NK model. With a protein sequence on $N$ sites, we say that evolution is fast (and we have a sudden leap) if after our fitness landscape changes, we can get to a new local equilibrium in a number of generations that scales with $log N$. Kauffman & Weinberger (1989) showed how this model can be used to study affinity maturation, and showed that to achieve a sudden leap we need high epistasis and low correlations between pointwise mutants. In particular, their model suggests that typical epistasis in the CDR is on the order of 40 proteins (out of the total 112 proteins in the CDR).
Clark, S.H., Huppi, K., Ruezinsky, D., Staudt, L., Gerhard, W., & Weigert, M. (1985). Inter- and intraclonal diversity in the antibody response to influenza hemagglutin. J. Exp. Med. 161, 687.
Crews, S., Griffin, J., Huang, H., Calame, K., & Hood, L. (1981). A single V gene segment encodes the immune response to phosphorylcholine: somatic mutation is correlated with the class of the antibody. Cell 25, 59.
Kauffman, S. and Weinberger, E. (1989) The NK Model of rugged fitness landscapes and its application to the maturation of the immune response. Journal of Theoretical Biology, 141(2): 211-245
Tonegawa, S. (1983). Somatic generation of antibody diversity. Nature 302, 575.
Correct answer by Artem Kaznatcheev on January 25, 2021
With all due respect, a few of these answers, although good examples of selection at work, were voted too high given the specific question asked: “documented examples of by evolutionary leaps being made, over the course of just a few generations?”
Sometimes we’re better being honest and identifying something as an ‘unknown’ or ‘yet to be observed’ than to list (and have people up-vote) poor examples. We do evolution a dis-service when we promote poor examples as answers to questions like these.
To expound:
The cricket losing the ability to sing (communicate) examples does demonstrate mutation and natural selection at work, but really only shows the REDUCTION of a capability. It’s not a good example of evolutionary leaps. It only happens to be beneficial in one SPECIFIC context. This would be analogous to tanks on a battle-field which communicate via radio, vulnerable to radio-frequency tracking missiles. Any tank with a broken radio would not be vulnerable to these missiles. Although technically ‘beneficial’ in this context, it’s an example of a loss of capability, not a gain of capability. We need to promote examples of mutations that PRODUCE capabilities.
Lactase persistence example likewise is an example of mutation and natural selection, but not a good example of a GAIN in functionality (as some have pointed out in the comments). It’s technically the loss of the normal switching-off mechanism of lactase production following weaning. So once again, a loss, that happens to have a beneficial side-effect.
Regarding punctuated equilibrium, I’m not surprised that was mentioned but was surprised that it got some votes. It’s a hypothetical explanation for why we see gaps in the fossils, but not conclusive ‘evidence’, or in the case of the question asked not “documented examples”.
Again: We do evolution a dis-service when we promote poor examples as answers to questions like these. Let’s focus on quality, not quantity when it comes to presenting evidence for evolution.
Answered by or1equals1 on January 25, 2021
I think that this might refer to evolution in punctuated equilibrium as described by Stephen Gould et al way back in the 70s. If this is the case, it refers more to the idea that changes and speciations can be quite rapid in time and for long periods you don't see morphological changes or speciation events in the record.
If so, then this is influenced by the study of evolution in cases where there are large changes in the environment very rapidly. The classic case is when there is a bare island and new animals arrive only rarely. This is all very much inspired by Darwin's observations in the Galapagos, but has since been studied quite a bit. In such cases you see just handful of sets of birds suddenly appear and you find a finch that can scrape bugs out of bark, another that can dig into narrow niches in the rock for food, where in a broader ecosystem two completely different species would be utilizing those 2 food sources.
It should be said that no evolutionary leap should be understood as an acceleration or deceleration of evolution. Only a change in the rate of adoption of variations because of a wider set of possible advantages those variations can represent.
Answered by shigeta on January 25, 2021
The ability to drink milk by the inheritance of lactase persistence via a single allele change. Sociology and genetic studies have shown that the immigration of a few lactose tolerant people into large non-lactose tolerant populations, the lactase persistence gene quickly spreads through the population, a sign of a dominant mutation and survival of the fittest at work.
Not in the mood to dissect the papers but here are a few commentaries:
Answered by bobthejoe on January 25, 2021
Zuk et al. (2006) document the rapid evolution of song-less crickets in a population of crickets that previously used song for courtship.
In less that 20 generations, over 90% of male crickets of the species Teleogryllus oceanicus evolved to a novel morphology ("flatwing") that rendered them unable to call to females. They hypothesize that this shift resulted from the presence of an North American invasive "acoustically orienting parasitoid fly."
Basically the flies detect calling males and parasitize them, rendering them unable to reproduce. Were it not for the presence of the parasitoid fly, the flatwing flies would likely not have survived. Non-calling individuals rely on the presence of calling males to bring females near for mating.
Answered by kmm on January 25, 2021
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