One thing I often hear regarding evolution is the notion that it can end. That is, I hear people make the claim that in one way or another, a species can (or has) reached a point where it will no longer evolve. This idea is generally applied exclusively to humans, but perhaps advocates would extend their arguments. I’m not sure. At any rate, it’s a surprisingly popular claim. Geneticist Steve Jones even made a version of it. He was speaking more of rates than anything, and I’m likely to chalk up his statements to hyperbole, but he did title one of his talks, “Human Evolution is Over.” Unfortunately for him, he’s wrong.
Evolution at its most basic is the transmission of genes from one organism to another. That isn’t to say individuals can evolve – they can’t – but broken down to its constituent parts, evolution is the flow of alleles from one vehicle (individual organism) to another. So long as that is occurring, evolution is occurring. To put it another way:
Evolution happens every single time an organism reproduces.
Evolutionary rates – generation time, mutational rate, environmental pressures, frequency of drift, etc – will vary from species to species and over great swaths of time, but they can never reach zero for any given population unless that population ceases to exist. At the point where members of the group no longer produce offspring is when evolution stops. It is literally the only time it can stop.
The fact is, evolutionary theory is the most integral part of the field of biology. The famous Theodosius Dobzhansky paper and now phrase, ‘Nothing in biology makes sense except in the light of evolution’, couldn’t be any more true; from the moment the first replicator evolved into something more, evolution has not once taken a break. So long as there is life, there is evolution.
Filed under: Biology, Evolution | Tagged: Evolution, Nothing in biology makes sense except in the light of evolution, steve jones, Theodosius Dobzhansky |
For the Sake of Science 
I’d have to disagree with you there, Michael. Evolution is genetic variation coupled with natural selection. Natural selection equates to increased or decreased birth / survival to reproductive age rates brought about by the genetic variation.
In our first-world society, just about everyone survives to reproductive age thanks mainly to medical care. People who would have died young in previous centuries because of, say, haemophilia, can now survive thanks to the likes of Factor VIII.
Greater or lesser intelligence gives nobody in our society an edge in survival rates, where in the wild a more intelligent person might better be able to find water during drought periods, but it comes out of the tap for everyone now.
Turner syndrome can cause infertility in women, but can now be treated with fertility treatment.
If anything, I would say (without espousing eugenics or other interference) that we’re effectively “devolving” by artificially selecting lethal genes.
In all practical sense, evolution is as you describe. However, that is in practice. In (nonscientific) theory, evolution needn’t be culled by any specific mechanisms. That means we should refer it simply as allelic change of time; the way by which it happens isn’t important here.
The only time allelic change does not occur is when there is asexual replication where the copy is perfect. Other than that, evolution occurs every time a new organism comes into being.
As for modern day survival rates, even if we ignore places like Haiti or sub-Saharan Africa, all we’re looking at is different selection pressure. It will be lessened in some areas, but it still exists. And, on the flip side, we can see how decreased pressure can still lead to change. For instance, with the advent of glasses, contacts, and LASIK, it would be reasonable to predict that the average person’s vision will become worse over time. That is an evolutionary change right there.
I agree with Alastair J Archibald in the definition of Evolution. And the truth is that human genes do not undergo any selection because of the phenomenon of panmixia. Therefore, the evolutionary rates for humans are as close to zero as they can ever get. Of course that does not mean that these rates are not a part of evolution, it is in fact a huge stasis with almost no perspective for any change in the future.
The specific mechanisms are not relevant here. Unless we’re talking about perfect replication, we have change from generation to generation. That is evolution.
Sorry, Michael, but I’m afraid I still disagree. To take your example of worsening eyesight due to glasses, etc., how does the worse eyesight become selected? People with glasses don’t have any reproductive advantage over people with 20:20 vision. Assuming eyesight is highly hereditable, the 20:20 guys will presumably continue to pass those genes on to their offspring.
There may be greater genetic variation due to the “artificial selection” I mentioned earlier, but no selection pressure favouring weak over acute eyesight.
Variation is indeed a prerequisite for evolution, but it needs to be partnered with a selected advantage or disadvantage arising from specific aspects of that variation.
For example, in the much-touted example of the pepper moth, Biston betularia, the genetic variation was pretty much constant, but the sooty trunks of Victorian ash trees gave the once-persecuted darker-shaded moths a distinct survival advantage.
With the advent of the Clean Air Act, the same variation re-selected the silver moths.
Darwin’s genius was not in discovering evolution, but in defining its source, and the kicker was natural selection. Imperfect heredity was just a ground rule necessary for N.S. to take hold.
It isn’t selected and it isn’t favored. The pressure has been removed (in most parts of industrialized areas). That means the alleles will move more and more towards poor vision just by chance. That is a change in frequency, and a change in frequency is evolution. Natural selection is the mechanism by which everything moves with ‘purpose’, but it and evolution are two different things. That’s a distinction I think I need to emphasize here.
I still see it as only an increase in genetic diversity, and that is just not evolution as I understand it.
Surely the whole point of evolution is the drive towards an undefined and unanticipated “goal”. I understand your use of the word “purpose” in its metaphorical, as opposed to teleological, sense, but evolution proper is surely a permanent change in a species (or even a speciation event) brought about by natural selection, not a mere increase in variety. Indeed, it seems that evolution is all about a limitation in diversity due to selection pressure.
Viz, drug-resistant bugs, as predicted by Fleming as far back the 1940s shortly after penicillin became widely available. It’s been artificially selected inadvertently through overuse of antibiotics, but the net result has been a culling of non-resistant bacteria: a reduction in diversity, since drug resistance is now increasingly the only game in town for viable bugs. The “winning hand” has been picked out of the pre-existing genetic melange. As evolution often appears to be, this looks to the uneducated like a “hey presto” sudden and permanent change.
A genetically highly-diverse species is one with no selective pressure towards a permanent “change”, meandering this way and that with no drive to any single direction. I can’t see in any way how that can be classed as evolution.
I’m not trying to be obtuse here, but selection pressure surely is evolution.
I don’t see evolution as simple culling. That is what natural selection does and, of course, that is what drives all the tremendous change we see, but it is that change that is evolution, not how tremendous is happens to be.
I certainly didn’t mean to imply that evolution is a mere increase in variety. As far as I’m concerned, total allelic variety can stay entirely steady and there will still be evolution. The only requirement is that the specifics change. That is, the total variety can remain constant so long as we don’t have perfect replication and I would call that evolution without hesitation.
We may end up agreeing to disagree on this one, Alastair. Selection pressure is one mechanism of of evolution, but the terms “natural selection” and “evolution” certainly can’t be said to be interchangeable. Plus we have to consider the other mechanisms. Genetic drift is random and without inherent direction, but it happens and it brings about changes sans selection pressure. Does that not cause at least some injury to your argument? We see evolution happening even when there is no pressure, so I do not think it is correct to define the process by its primary mechanism.
I can certainly see that over time, random “purposeless” genetic variations could make the alleles of a breeding group incompatible with those of their former peers, say by geographic isolation. And I’d agree that that is evolution without natural selection.
But even an isolated cauldron of bubbling micro-changes is unlikely to cause speciation in modern human groups. Humans have never been so mobile. Next Friday, I’m hopping onto a metal tube and being whisked over half the globe to China. I will expect to see people of many races in PuDong, Shanghai, as I do in London, New York, Adelaide, Mumbai…
Genetic variation cannot cause a change to become “permanent” for one group within a large, widespread breeding group. Denied even geographic isolation, the human race is not being genetically propelled, in however gentle or undirected a manner.
Surely, for any allelic change such as poorer eyesight to become “locked in”, it needs either:
To become ever wider-spread within a contiguous breeding group due to differential breeding frequency or survival
or
To become isolated from the larger former breeding group, e.g. by tectonic drift.
Modern humans don’t have either of these options. We don’t have either differential selection pressure or the opportunity for one breeding group to lock itself away from the wider gene pool.
I’m happy to call difference of opinion, but I’d rather see your (allelic?) drift.
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