Elephant poaching has been around since long before the Mozambique civil war. The number of tuskless elephants may have been at 2-4% prior to the war, but that doesn't mean that lower levels of poaching didn't push it up to that level from some much lower naturally-occurring level.
2-4% seems like a _very high_ rate for a trait that could negatively impact a female's chance of survival AND kills 100% of her male offspring.
https://nhatrangbay.net.vnwww.eaza.net/assets/Uploads/EAZA-D...
When I think of selective breeding I think of humans picking out which animals (cows/dogs/wheat/etc) get to reproduce.
Probably because the concept of "nature" no longer serves any purpose if you don't, as it doesn't exclude anything.
It's often a pointless distinction to make (see also: anything that labels itself as "organic"), but it's a convenient shorthand to describe a category of interactions that people often want to talk about.
"They identified two likely genes AMELX and MEP1a, which are passed from mothers to the offspring on the X chromosome. But if a disrupted gene is passed in a male elephant, the elephant dies; the female elephant would instead evolve to be born without tusks. "
What would be the effect of this on male elephant population when taken to the limit (i.e. 100% of females are tuskless)? Seems to me that it'd skew the proportion of births towards 2:1 (assuming it's now at 1:1)? How significant impact would that have to the species as a whole?
So while a tuskless female may generate 2:1 females to males, that's (hopefully, depending on poaching) far from a stable birth ratio for the population, though active poaching may cause the female to male ratio for living specimens can be further skewed much higher than 2:1.
Basically, when using sexual reproduction, it _would_ be highly effective for the species to have many more females than males, since females are the bottleneck of population growth. However, if the sex ratio is skewed then any traits which increases the likelihood of male offspring will enjoy a reproductive advantage (because the male offspring will itself have more offspring than the females), spread through the next generation, and reduce the sex ratio, until it reaches the balance of 50/50. This applies whether the trait is dominant or regressive, etc.
So in this scenario, as the tuskless mutation spreads, the number of males decreases and the genetic advantage of having tusks grows, until it balances out the genetic disadvantage of losing females to poachers.
I think you are making a good case for that conclusion, and would that not imply that the mutation - or, more specifically, its most recent manifestation - arose fairly recently, i.e. subsequent to hunting for ivory becoming a serious problem for elephants?
For anyone else wondering how this is possible on an individual level, apparently a lot of people used to reproduce with their first and second cousins.
Alice has a son, Eve has a daughter.
Alice's son knocks up Eve's daughter.
Their kid will have two biological grandmothers, but only one biological grandfather.
Apparently, historically, this type of thing was quite common and could heavily skew family trees towards the female side of things.
Let's adjust the example above slightly to include Bob's friend Darren, who who never got laid because he spent his whole life watching pornography and playing video games.
Even in this case, despite the 50:50 ratio of males and females both across society as a whole and within each generation, the child has more male ancestors.
This will be the case for any sufficiently large population where males have more variance in reproductive success than females, and people (of either sex) reproduce with others who have a shared ancestor (the closer the ancestor, the greater the effect the variance has on the ratio of male to female ancestors).
(im not a historian so this is speculation)
I imagine that early humans had divided roles, and roles assigned to males involved more danger. (bearing in mind that the state of medicine meant that relatively minor incidents by our standards could lead to infection and death in theirs.)
So populations start out 50/50,but skew badly once men age enough to take on dangerous work.
This leads to men having multiple partners and the scenario mentioned in the sibling comment.
I thought it was 2:1.
Later on they mention that if this genetic trait gets passed on to males, they die. So along with hunting, males are doubly at risk.
It may be advantageous for the survival of an individual to be born without tusks, but it doesn't sound too good for the survival of the species.
Traits that are rare, are often rare because of shortcomings. But if environmental changes make that tradeoff worthwhile, it can be made. Meanwhile, evolution doesn't stop. Once the trait/gene is common there is positive selective pressure on complementary genes. Over time, these may mitigate or compensate for the negative traits that have acquired.
Of course, on the timescales that humans tend to selectively pressure species, there isn't time for all this elegance to emerge, usually.
My parent said:
> And this is why genetic diversity is a good thing.
I guess what I meant was: genetic diversity is a good thing. But this particular case is not a great example for illustrating why.
It may be the case that at least one typical X chromosome is necessary for survival, and males only get one X chromosome.
Words like "natural" and "artificial" don't admit tidy definitions, and you know that, which is why you demanded that I define it for you, presumably so you could poke holes in whatever definition I provided.
Not really. Your original use of the word implied the definition you were using, and my comment was merely to point out that it's the wrong definition (in my opinion, obviously).
In this context it makes more sense to include the intention, because the evolution itself in this case is not something we artificially induced.
The elephants, for example, might have evolved to have green tusks instead, which would have made them not attractive to poachers. They could have grown wings that would made them more difficult to be hunted. The point is, poaching might be artificial, but the elephants responded to a threat (coming from humans or not) with a completely random and natural process.
That's precisely what I said... you asked me to provide the definition in order to poke holes in it. Rather than go through this back-and-forth nonsense with implications, why not just say it up front?
Anyway, seems like you think I was saying that the evolution was artificial. Evolution is heritable variation and the forces that choose among those variations. Natural selection, artificial selection, and genetic drift are possible forces that choose the variation, but in this case, the variations themselves are still random mutations.
You can't peel off the "natural" in "natural selection" in this case and say "because this is done by humans, it's artificial selection," when artificial selection already has a distinct meaning.
[0]: https://en.wikipedia.org/wiki/Selective_breeding [1]: https://www.nationalgeographic.org/encyclopedia/artificial-s...
If I were a philosopher, or if I wrote dictionary entries, I might decide to spend the time to come up with a rather clever definition for "artificial". Feel free to come up with a definition yourself, if that's your fancy.
People trust traditional techniques of preparing food because they have proven successful at their intended goals. When you start messing with people's food, they become suspicious as to whether you know the full repercussions of what you are doing.
So the injection of a novel element is considered "artificial" - despoiling the "natural" -- e.g. time-tested technique, and possibly disturbing something fragile -- e.g. human health.
Similarly, people are quite reactionary when it comes to open spaces and nature because they see a system that appears to be in balance and has survived the test of time. They oppose altering the current state of affairs because they are sure some unintended side effect will screw things up.
On the one hand, it's laudable to have these goals, but if they used the standard language of conservatism, traditionalism, etc, they would be branded as reactionaries, so the spirit of the age is to invent new words like "artificial" and "natural" that are less loaded with politics, even though it is all just conservatism at its roots.
I ask because it’s not a change in the genetic structure of elephants. It’s an existing trait becoming more wide spread.
There are no new species and there is no change to genetic code
It is not uncommon, in forums like HN, for there to be arguments over the 'true' definition of a word, but unless the issue being debated is lexicographical, these arguments are usually missing the point. While it is the case that the teaching of a subject often begins with some definitions, that is only the beginning, and it is usually done to shortcut the difficult process by which those definitions came to be written in the first place. On reflection, it should be clear that the definitions cannot be written (or, at least, finalized) until after we have gained an understanding of that which we are defining.
What we are observing here is the selection part of evolution. We did not observe the origination of the mutation causing the trait being acted on by selection, but it is empirically established that it is not uncommon for such mutations to occur. Nor have we seen it play out fully, where the trait, and the mutation causing it, become ubiquitous, and other alleles disappear (if the selection pressure continues and the species does not become extinct.) Here, we are observing evolution in progress, not its ultimate result.
This change alone will not create a new species, but if enough changes occur that the descendants could not, in principle, breed successfully with their ancestors, then it has. We can see a precursor to this in the mutation being lethal in males.
natural selection, i.e. the environment they're born in, is what picks winners and losers among those inherited characteristics and mutations.
Almost all individual mutations on a genetic level are benign. It's the combination of (selection of specific trait + compounding change) that is what we know as evolution.
In this case, the "change to the genetic code" produces elephants without tusks. That happened by change. But now, the elephants without tusks are the ones who get to live, because they're not poached. That specific mutation allows them to live/thrive. In the same way better hearing might allow a bird to evade its predators.
"no change to genetic code" ignores the fact that there are elephants wandering around who don't have (and will never have) tusks. (also: evolution is quite slow. this by any right is a huge, "forced" evolution. not in that we forced a change in the genetic code through editing it, but we are changing the course of genetics in a species through our collective behaviour).
Try this resource instead: https://evolution.berkeley.edu/evolibrary/article/evo_01
It's like market share. More users can simply download your software and you can gain market share without releasing an update.
Like others said, it's evolution + natural selection. In this case the evolution part came long ago and now natural selection is making it more prevalent.
-- 18.5% of females were tuskless before the war
-- 50.9% of females were tuskless after the war
-- 33% of females were tuskless in the first post-war generation
Of the offspring:
-- 8.7% of females born to two-tusked females were two-tusked
-- 44.7% of females born to tuskless females were tuskless
... were tuskless, you mean?
It makes me suspect there's something else going on here that's not just good old natural selection.
Have they done any tracking to confirm the tuskless elephants are actually being born to tuskless mothers? Or could it be that the parents are actually affecting the way their offspring are born in some lamarckian-esque sense? If there'd be some trick animals can pull to change their offspring in some ways, that ought to be highly effective for long term species survival and should thus be highly selected for.
If a new predator is introduced to a population that selectively kills only certain traits, that mutation can become dominant in the population within just one or two generations.
Imagine if aliens came to Earth and killed everyone over 5'6" tall. That "evolution" would be essentially instantaneous.
I think it is ridiculous to think that more elephant are born without tusks as a kind of "random selection" or even adaption
I imagine the poaching process doesn't actually differentiate tusked and tuskless elephants, both types of elephants would fall into the trap and die? And then if it has tusks the poachers take them, if it doesn't have tusks the poachers just abandon the dead elephant?
Or does their trap actually trap them by the tusk?
The poacher could always hang around near the trap, but if you're doing that you might as well just shoot the elephant, not trap it.
Edit: I found an article[0] describing some poaching methods and apparently they do use traps! Including snares and a spiked board. But that it appears homemade shotguns and rifles are the most common method.
[0] http://www.open-earth.org/document/natureR_main.php?natureId...
Are 100% of tusked females giving birth to 32% of the newborns without a tusk?
What % of tuskless females give birth to tusked females?
So it's a significant change, but it's not like this property was coming out of nowhere. It started off about as common as humans having green eyes.