I asked my masters in the Freethoughtblogs collective, because there are (I believe) some evolutionary biologists in the house. However, I don’t want to turn this into a case study of “what happens when you ask a scientist a question?” [because the answer is usually “maybe” or “that’s bullshit.”]
Over at Vice, there is a report that some elephants have evolved to be tuskless, due to the evolutionary pressure caused by poachers/hunters. [vice]
Elephants in Mozambique are evolving away from having tusks due to pressure from rampant poaching over decades, according to a daunting new study.
Published in the journal Science on Friday, the report from researchers across departments at Princeton University, the non-profit ElephantVoices, Gorongosa National Park in Mozambique, and the University of Idaho, analyzed survey data that suggests natural selection has favored tusklessness in female elephants – a rare genetic trait that has become more common – amid high rates of poaching and population decline.
I always thought that evolutionary changes are slow(ish) and elephants haven’t really been hunted to near-extinction prior to the 1800s. (Probably a combination of cheaper/faster travel and the development of massive empires with a wealthy class that can afford to travel someplace for their bloodbaths) – so I asked the FtB HiveMind(tm) and I got a kind of “well… maybe.” One thing I hadn’t thought of is that the population of elephants in some areas are very small, which amounts to an “evolutionary bottleneck” – changes ripple through small populations faster. So, it could be.
The researchers took scans of the entire elephant genome and located two genes associated with tooth development in mammals, both of which guide the formation of enamel, dentin, and other materials necessary for tooth and tusk development. One of the genes – AMELX, which provides instructions for the creation of a protein called amelogenin – was found to be associated with selection pressure due to poaching.
The team undertook the study after observing both growing rates of tusklessness among female elephants and severe population declines (2,542 elephants in 1972 whittled down to 242 in 2000) among both sexes in Gorongosa National Park. A civil war in Mozambique from 1977 to 1992 killed off some 90 percent of the country’s elephant population, the paper notes, as armies on both sides of conflict targeted the animals for ivory. Though tusklessness is currently considered a rare genetic trait in female African elephants, they’re significantly less attractive to poachers. Tuskless elephants are therefore much more likely to survive, passing on the tuskless gene to their offspring, who pass it onto their offspring, and so on. The paper notes that as the population of elephants took a nosedive, there was a threefold increase in the frequency of tuskless females.
242 elephants is a tiny population; that’s a hell of a bottleneck. Apparently early proto-humans experienced a similar bottleneck, in which it came down to 6 females that everyone alive today descended from.
I’m not too encouraged for the fate of the elephants, though. As we’ve seen from NRA executives, basically nothing is safe from the “killing as entertainment” crowd; the elephants are going to have to evolve to not have feet, next, so Wayne LaPierre can’t turn them into umbrella-stands. Someone ought to hunt him, because apparently he likes that kind of thing.
Exactly what I thought when, several years ago, I saw a sickening picture of the frogspawn of the Orange Idiot displaying some big cats (leopards maybe, I don’t remember for sure, and I damn sure am not going to look up the photo) that they had hunted and killed. I thought it would be poetic justice if those two idiots were turned out into the the wilds of Africa with no guns or knives and became prey for the leopards.
This makes it sound like there was a time when there were only 6 female proto-humans.
The “6 females” number comes from studies of mitochondrial DNA, which only comes from one’s mother. What this says is that if you trace everyone’s ancestry back along the female line — i.e., mother’s mother’s mother’s etc. — you’ll eventually find one of 6 different people. That doesn’t mean there were only 6 women around. (Remember, a person alive today has many, many, many ancestors back in the days of protohumans.) What it means is that if you follow any other female protohuman’s “descent tree,” at some point, each branch ends up with a woman who either had no female children or those female children never had children.
This could, in principle, happen with no evolutionary bottleneck at all, although it sounds a bit unlikely to me.
You don’t have to go to Africa to see the same effect, or Japan’s heike crabs, as Carl Sagan noted. US commercial and “sport” fishing kept targeting the largest fish, even within the same species. After decades of this, the result is only the smaller ones survived and now make up the bulk of the populations.
https://psmag.com/environment/fish-stories-the-ones-that-got-away-3914
I think that another point to bear in mind is that selective hunting by humans is much more selective than most other forms of natural selection.
… elephants haven’t really been hunted to near-extinction prior to the 1800s. (Probably a combination of cheaper/faster travel and the development of massive empires with a wealthy class that can afford to travel someplace for their bloodbaths)
Perhaps today the “’killing as entertainment’ crowd” constitutes a lot of the elephant-extinction factor, but historically most of that came from the $$$ demand for ivory (conveniently transportable and with indefinite storage life). Blame the scrimshaw artists, chess set makers, and – above all – piano manufacturers.
I think this is an excellent case of showing how evolution usually works – i.e. not waiting for some new mutation, but by selecting from an already present gene pool. In such a case, evolution can happen really fast, in a matter of just a few generations, or even one.
One problem with this particular case is that the genes involved are dominant, on the X chromosome and seem to be fatal in males. That means the population cannot become completely tuskless unless novel mutation(s) occur(s) that make(s) these genes tolerable for males too. And that would take a longer time, probably too long for the population to survive. So if this particular selective pressure continues, the species will be doomed to go extinct in short order at the precise time when the last living male with tusks gets shot.
A second problem is that tuskless elephants might be viable as individuals, and eventually even as a population, but they do not occupy quite the same ecological niche as tusked elephants. I do not know enough about African ecology to say whether elephants are keystone species or not, but as the article states, they definitively have a big impact and tusks play a role in that. Change of elephants from those with tusks to those without would of course be less disruptive than downright extinction, but it still would be bad.
https://en.wikipedia.org/wiki/Peppered_moth_evolution
@3: https://decapoda.nhm.org/pdfs/3729/3729-001.pdf
The speed of evolution will depend on the strength of selection. What this means is that the population pressure on the elephants due to ivory harvesting is very strong.
I just feel depressed about hunting elephants. It’s logical that taking the animals with large tusks will lead to reduced tusks.
All of the various domestic dogs are the same species, they just look very different due to human selective breeding.
It’s the same with white tail deer. There is a branch of trophy deer hunters who noticed that selectively hunting bucks with the largest antlers was resulting in smaller antlered bucks.
They changed the rules to protect the huge old bucks, and started managing the hugely overpopulated deer herd by issuing doe permits instead of just hunting the bucks.
I’m not a hunting enthusiast, but I’m glad that the people who do hunt are interested in keeping the deer herd healthy, even if they only do it because they dream of huge trophy racks.
Too bad that the same isn’t true for the poor elephants.
“elephants haven’t really been hunted to near-extinction prior to the 1800s.(Probably a combination of cheaper/faster travel and the development of massive empires with a wealthy class that can afford to travel someplace for their bloodbaths)”
I donno about that. The mammoths and the mastodons and the gomphotheres were hunted to extinction slightly before then. As much as I like to blame things on wealthy colonizers, driving big animals to extinction seems like a more widespread problem.
because of their propensity to travel and their excellent swimming abilities, elephants often colonize islands, where founder effects, population bottlenecks, and selection pressure drive remarkable (and often quite fast!) evolutionary changes. Pygmy mammoths evolved independently on many islands, and survived on Wrangel Island until ~4000ybp. Pygmy elephants were likely the original food source for Komodo dragons, before humans introduced deer and buffalo
Marcus:
Apparently early proto-humans experienced a similar bottleneck, in which it came down to 6 females that everyone alive today descended from.
That is a misconception. There likely were population bottlenecks, but that’s neither here nor there. There were plenty more individuals alive at the time those six were alive, it just happens that none of their genetic material survives today. This is probably about mitochondrial DNA, which is just a small subset that’s easy to trace because it’s inherited only matrilineally. The Mitochondrial Eve Wikipedia page has a useful section about misconceptions. The Most recent common ancestor page is slightly mind-bending but makes the point in a different way.
I always thought that evolutionary changes are slow(ish)…
Well, as you admitted, the initial variation — lack of tusks — had already happened, long before poachers started selecting.
Not sure if this adds anthing particularly new but Aussie ABC has coverage of this here :
https://www.abc.net.au/news/science/2021-10-22/elephants-ditching-tusks-to-escape-ivory-poachers/100406480
(An extra confirming source of info if naught else I guess?)