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I'm trying to layout a scientifically correct evolution path for the octopus to develop intelligence on the post-human Earth. I'd like to know if it's possible for an octopus mom to choose, or use other environmental factors (temperature, oxygen level, etc) to impact its egg or hatchling's gender ratio? I hope that's possible as some sources say octopus do not have sex chromosome.

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    $\begingroup$ off tangent but ''There are three plural forms of octopus: octopuses, octopi, and octopodes. Currently, octopuses is the most common form in the UK as well as the US; octopodes is rare, and octopi is often objected to as incorrect.'' $\endgroup$ – EveryBitHelps Mar 26 '18 at 20:03
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    $\begingroup$ Now this is a question for which I'd really enjoy seeing some answers :) $\endgroup$ – Renan Mar 26 '18 at 20:05
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    $\begingroup$ AFAIK the mechanism for sex determination in cephalopods is not yet understood. It may be that sex is determined by environmental factors, or it may be genetic (in which case experimental work suggests it's oligogenic). In addition it seems that secondary sexual attributes are determined by a mechanism separate from that which determines sex. (Here is a report of a functional female which looked like a male from the outside.) $\endgroup$ – AlexP Mar 26 '18 at 21:32
  • $\begingroup$ Wouldn't the most limiting factor be size and age? From what I know, Octopuses are already highly intelligent but don't have the lifespan to actually start using it to full effect. Having a brainsize similar to ours would also help, so the Giant Octopuses might offer a solution with enough space in their bodies for a larger brain. $\endgroup$ – Demigan Mar 27 '18 at 7:43
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    $\begingroup$ I believe the most limiting factor is not necessarily age, but that Octopuses are left to fend for themselves from birth onward, each having to essentially learn everything anew. I read something that said that thanks to pollution the Octopuses are being forced to live closer together, and so the older ones are starting to teach the infants. Maybe octopus society is not as far off as one might think. $\endgroup$ – Callum Bradbury Mar 27 '18 at 9:39
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I'm trying to layout a scientifically correct evolution path for the octopus to develop intelligence on the post-human Earth.

We don't really know how evolution works in the sense of being able to make a scientifically correct path. And there can presumably be many paths leading to the same end result (intelligence).

I'd suggest that for a human-like intelligence the key stage is the development of some form of sophisticated communication to act as a language. Evidence in people born deaf suggests that if they are taught any form of communication (typically sign language) they can develop an inner voice which allows for the development of an active intelligence and without this they do not. It seems to be a key step in our development. I'm not really familiar with communication between octopi but I gather that they have some relatively developed features in this sense.

So you probably just need them to continue to develop better communication and tool handling skills from the ones they already have. Mucking around with sex (as usual) will just complicate things. :-)

I'd like to know if it's possible for an octopus mom to choose, or use other environmental factors (temperature, oxygen level, etc) to impact its egg or hatchling's gender ratio ?

I'm not aware of Earth octopi having this capability now, but if you're writing about them in some future they could always develop such an instinct.

However a likely flaw here is that there's no evidence to suggest male or females are going to be more or less intelligent on average. At the very least this kind of story based decision would be politically incorrect and draw a lot of the wrong type of criticism. I'd suggest caution with this idea.

The problem with exploiting any such mechanism is that initially your octopi will not have self awareness sufficient to make a conscious decision. You're really better off developing a mechanism that relies on either random chance (and works out at the required ratio) or having them develop a systematic biology that does the job (e.g. first they produce predetermined male eggs, then female eggs in turn). Some mechanism that does not rely on "making a decision" in creatures that we would assume don't have such high level of conscious thought.

I hope that's possible as some sources say octopus do not have sex chromosome.

As a side note I'd suggest you link to your sources in your questions for those sort of statements. Doing that will likely get more interest from people in your questions.

This doesn't really make much difference to your intention. Even if they did have a chromosome that determined sex, or a group of them, this might be manipulated by e.g. diet - choosing a diet that's richer or poorer in certain chemicals than normal for a period prior to mating. It may even be an easier mechanism to create (in a book that can gloss over details a bit) than something else.

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In the last couple centuries, many cultures around the world would kill a newborn in the case twins were born, or if the child is born ill or with malformations. This happened in Japan up to the 20th century (mabiki), in Australia, in Africa, and in some indigneous tribes in South America it is still practiced today.

What the expletive does this have to do with mollusks?

Humans usually bear one child at a time, sometimes two. More than two children in one pregnancy is rare, and more than eight fetuses in a human womb is unheard of.

Cephalopods, on the other hand, are spawners. They may have thousands of children from one single fertilization, and only a few are expected to live to become adults. Were them to develop intelligence comparable to ours, it is not a stretch to expect their views towards abortion and infanticide, at least regarding their own species, to be much different from humans'. These might be generally more acceptable to them.

To make myself clear: just as there is no general consensus on the ethics of abortion between humans, there might be no consensus in a cephalopod society. But I believe the cephalopod society would be, in general, more accepting of it. As for infanticide, it has been a thing among humans, I think it would be a thing among them too.

So if a cephalopod family wishes to have more male or female offspring, they could resort to different methods.

  • Before technology allows them to probe a child's sex during egg and larvae stages: They can wait until a larvae is advanced enough to show primary sexual characteristics, and dispose of the larvae in some way. That would be infanticide.

  • After technology allows them to probe a child's sex during egg and larvae stages: They can simply discard the eggs they don't want. That would be abortion.

There is indication that sexual determination in mollusks is oligogenetic (see AlexP's comment in the question). If so, they might one day acquire the technology to do fertilization in vitro, using gene markers to find out which gametes have the genes for the desired sex. That way gender rations could be adjusted without neither infanticide nor abortion.

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    $\begingroup$ That's exactly what I plan to use as the core of the conflict. Octopi gain intelligence, this competitive edge increases their offspring's survival rate. They basically deplete resources of the entire ocean before they advance into tech age. To limit population brutal infanticide is practiced, and the hero is a small octopus to put an end to it. $\endgroup$ – A.Z. Mar 27 '18 at 17:25
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Sex ratio is more or less irrelevant.

your biggest issue with octopi is getting them to stop ding after mating, It is hard to evolve child rearing when you are not alive at the same time as your offspring. Only getting to mate once also locks you into having many many offspring at once (r strategy). Since we don't know why they die after mating you can get away with hand waving such an alteration.

Once this happens something like mimic octopus could get a lot of benefit from teaching their offspring different mimic techniques which will go a long way to intelligence, as it gives high returns for evolving language, empathy and the like, and could even encourage pack hunting to evolve.

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