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Except it's only advantageous to female elephants, according to the article: "They identified two likely genes AMELX and MEP1a, which are passed from mothers t
by bialpio 5y ago
Except it's only advantageous to female elephants, according to the article:
"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?
- esturk 5y agoMaybe not as much as you would think. Naturally, not all males mate and the mating ratio is not always 1:1. Take humans for example, it's been shown our ancestors comprise mostly of females in a ratio roughly 3:2 to males. That is, some male ancestor probably mated with more than one female ancestor somewhere.
- thaumasiotes 5y ago> it's been shown our ancestors comprise mostly of females in a ratio roughly 3:2 to males. I thought it was 2:1.
- caymanjim 5y agoI don't know what the numbers are like for elephants, but in many species, most males don't get to mate at all, and a handful of dominant males mate prodigiously. Even if tuskless males were viable, they'd fail miserably at mating if there were tusked males around, because they'd get their asses kicked.
- AussieWog93 5y ago>our ancestors comprise mostly of females in a ratio roughly 3:2 to males. 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.
- manquer 5y agoStill not that uncommon in few parts of the world.
- TedDoesntTalk 5y agoI do not understand how mating with a 1st or 2nd cousin affects the ratio of females to males. Could you explain?
- AussieWog93 5y agoAssume that Bob knocks up both Alice and Eve. 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.
- tehjoker 5y agoThat skews the tree shape, but the odds of each baby are still ~50/50 so the overall population numbers should be stable.
- dotancohen 5y agoAussie was demonstrating how an individual could have more male ancestors than female ancestors. And his very simple example did in fact provide the 3:2 ratio that was previously mentioned.
- tehjoker 5y agoI think I misunderstood the proposition. Sorry.
- AussieWog93 5y agoThe overall population is roughly 50:50, but men are more likely to be the "final node" in the family tree. 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).
- lvass 5y agoWarning: guesswork. If only females survive with this disruption, it can only be inherited from a mother, so only 1 X chromosome of a female can have it. If somehow only those females survive, there's a pool of 50% of X chromosomes of females with the mutation. The following generation would be born with half of the female population with the mutation (25% of female X chromosomes), and half of the male population dead. The following one, without artificial selection, would have a fourth of mutated females and dead males. So this mutation tends to just disappear without selective pressure. 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.
- mannykannot 5y ago> So this mutation tends to just disappear without selective pressure. 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?
- piaste 5y agoI'm a layman in genetics, but I believe the effect you described is what is known as Fisher's principle. 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.