This is a video after my own heart, since it’s about speciation: the splitting of a single lineage into two or more lineages unable to exchange genes. The question at hand, since this series—put together by PBS and “It’s Okay to be Smart”—is a long refutation of common creationist arguments, is this one: “Can we see new species form in real time?” For some reason creationists favor real-time rather than historical evidence, for we already have ample evidence of lineage splitting from the fossil record, from genetic data, from vestigial organs and embryology, and from biogeographic distributions. Well, creationists wouldn’t really accept any data, but they prey on people’s tendency to put more weight on stuff they can see happening with their own eyes.
At any rate, there is other evidence for real-time speciation beyond this, particularly involving polyploidy: the creation of new species (usually in plants) by the doubling of an entire genome. Such doubling can occur within either a pure species (“autopolyploidy”) or of a sterile hybrid (“allopolyploidy”). Matthew Cobb wrote about a new allopolyploid plant species on this site in 2012, and there are several other examples in my book Speciation, coauthored with Allen Orr.
The video is pretty good, emphasizing the importance of geographic isolation in speciation (i.e. allopatric speciation). We have very little evidence for speciation occurring between populations that live in the same area and are able to exchange genes while they diverge (sympatric speciation). To get genetic divergence extreme enough to make species genetically isolated, they must usually begin as populations that are geographically isolated.
There’s one big error in this video: at about 1:05 the video conflates genetic drift (the random changes in gene frequency due to sampling error) with natural selection. Both can contribute to speciation, but selection is thought to be much more important (see chapter 11 of Speciation).
Another mistake in the video is its claim that we were reproductively isolated from “our Neanderthal cousins.” That’s not true, of course, for many of us carry some genes from those cousins, and if that’s the case then our ancestors not only hybridized with Neanderthals, but the “hybrids” were fertile—allowing them to inject those Neanderthal genes into the genome of our ancestors. In other words, we were not reproductively isolated from Neanderthals. I would thus categorize Neanderthals as a “race” or “ecotype” or “subspecies” of H. sapiens, one that went extinct for reasons unknown. At any rate, this series could have used a bit more input from evolutionary biologists.
If you’d like to read about real-time speciation in British mosquitoes, click on the image below to go to the relevant paper:
How does genetic drift occur without natural selection?
Drift is the component of evolutionary change that is truly random. If two alternate versions of a gene (alleles) are present in a population, and neither allele provides any fitness advantage, the relative frequency of the alleles varies randomly in each successive generation through “sampling error”. In fact, given enough time, it is inevitable that one or other allele will be lost completely, and the other will be “fixed” in the population. This is the same statistical process that accounts for the fact that in isolated villages with little migration in our out (historically in Italy for example), it was common for almost everyone to have the same surname.
https://en.wikipedia.org/wiki/Genetic_drift
It is particularly important at the molecular level where the large majority of DNA mutations are “neutral” – they have no effect on the fitness of the organism, they are not subject to natural selection. It means that DNA evolution is random to a good approximation, and amenable to statistical analysis. This is extremely powerful when we compare the genomes of different species. It allows us to make quantitative as well as qualitative statements about evolutionary relationships.
https://en.wikipedia.org/wiki/Molecular_clock
Yes, but also alleles that are under selection will also experience drift while still under selection. As a general rule, even alleles that are strongly selected for- or against will be no match for the power of genetic drift in the case of small populations.
My brief use of Star Wars dialogue just now is b/c I just got back from seeing the new Star Wars movie. I am still geeking out.
As a small-time apple grower, one of my evolutionary “heroes” is a pest we have to be concerned about: the Apple Maggot Fly. Formerly Known As Haw Fly, this little fruit fly (with lovely, spider-mimicking wing stripes) fed only on Hawthorn trees, until colonists introduced the apple into New England in the 18th century. Then the little critter evolved a new life cycle, enabling it to feed and mate on apples rather than haws. This is “sympatric speciation” at its finest…and the rest is evolutionary history…and a real pain in the ass for apple growers who have to spray now for apple maggots..
I think that the thinking is that they have not completely speciated. It is a case of ‘incipient’ speciation.
Rhagoletis pomonella is covered extensively in Speciation, if you want to learn more, at least of the research as of 2004. There is a discussion of why this may not actually be sympatric speciation.
Thanks for the comments, guys. Is Speciation suitable for a lay reader?
To the extent I’m able to judge (and, warning, I’m an evolutionary biologist), yes. It seemed quite accessible to me, and I’m pretty sure you would get a lot out of it even if you had to bleep over a few bits.
I am not a biologist, and I found it quite readable. It drills down into more technical details though, compared to something that would be aimed at a lay audience.
Amazing how evolution deniers play the “we weren’t there to see it happen” game with evolution and then they’ll tell you they know that Jesus rose from the dead because the Bible says there were witnesses who saw his empty grave.
A hit, a very palpable hit!
Well played, sir.
Thoroughly enjoyed both this piece and the original article to which you refer, and have ‘pressed’ the original article on to my London transport themed website, http://www.londontu.be 🙂
I am so proud of myself…when they talked about “genetic drift” I could just see Larry Moran cringing. Then I read your commentary.
People like you and Professor Moran really are teaching us something! 🙂
It baffles me. Why neanderthals and sapiens should be categorized as subspecies? What is the crucial difference between these humans on the other hand, and coyotes & timber wolves or polar bears & grizzlies on the other hand. These carnivores produce fertile offspring, don’t they? We nevertheless think them as different species for obvious anatomical and ecological reasons.
Isn’t there ample evidence that shows neanderthals had a slightly different niche than sapiens? And anatomical differences are self evident. For example:
http://www.sciencedaily.com/releases/2015/12/151207131517.htm
Well, the Neanderthals did, for a long time, inhabit different areas with different climates, and also had appreciably different skeletal characteristics. From their material culture (tools, dwellings etc) they also seem to be significantly different in behaviour. Having noticeable, consistent and heritable differences is clearly not enough to be sure that complete speciation (i.e. reproductive isolation) has occurred.
In palaeontology, looking back at specimens from a million, two million, a billion years ago, we have to be aware that we’re only seeing one part of the structure of an organisms. While we’ve got the shape of the bones, we don’t have the colours of the bones, most of the soft tissues (though we may have the insertion points of suspensory ligaments and tendons) … we have to be aware that we’re dealing with a “morphological species” based primarily on the bone shape, but do have to be aware that that does not necessarily map perfectly onto the reproductive/ genetic definitions of “species”.
One recurring example of the problems that come with this are issues where people are debating – with varying degrees of evidence – whether already known morphological species might actually represent the different genders of biological species which are sexually dimorphic. If you compare the skeletons of adult gorilla, and completely lost the social cues, you might actually classify them as separate species. (Hmmm, maybe not a good example – would the birth canal be obvious enough in the skeleton to notice that you’d only got males in one species and females in another. Perhaps giant tortoises might be a better example.)
Bringing up the various types of wolves, polar bears versus grizzlies, etc are appropriate. Are they actually separate species? Good question.
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