[Jasmine1]

hello every one new here , I just read a interesting things, that is about the dolphin killing the porpoise around Cornwall. Is it due to both looking for the same food? Some dolphins were killing young to bring their mother back into season, did't know they did that thought they were more social than that? I saw there are few people appy it, so is it the fact, so it exit ??

[cabbage]

Hi and welcome to the forum

As far as I know (and I'm about the furthest thing from an expert you're likely to come across on this board) the dolphins aren't killing porpoises for food or due to competition for resources, they don't eat the same things.

I don't think anyone knows why they do it but the best explanation I've seen is that it may just be pure aggression - or even something akin to 'fun' or play for dolphins to hunt and kill porpoises. I believe I've read that they often play with the carcasses afterwards. Perhaps it could be a learning thing? A way to hone or develop fighting skills used against other dolphins? Mistaken identity? Its all speculation really.

I've wondered in the past wether the capacity for, or even enjoyment of, 'non productive' violence may be some sort of function or side effect of intelligence in a species (not necessarily in the actual individual involved of course!) I believe chimps are known to do similiar (to monkeys though, not to porpoises!) and of course humans... well that doesn't even need said.

Killing infants to bring females into season is well recorded in many species. Lions are quite famous for it despite (or because of) their social nature, as are wolves I think. Dolphins are known to be pretty sexually aggressive, I suppose the two traits would fit? It could also be done if the animals are struggling for resources, killing infants could reduce competition either for the animal itself or for its own offspring.

[Hawk_Eye]

I've heard similar stories. Dolphins can be very agressive toward other dolphins with larger species attacking smaller ones even attacking their own species.
Cabbage mentioned chimps. I remember seeing a programme, possibly Chimp Diaries, where a troop of chimp went out to patrol their territory and heard a bordering troop nearby. They went on to attack them killing and eating one or two I think.

[cabbage]

I've heard similar stories. Dolphins can be very agressive toward other dolphins with larger species attacking smaller ones even attacking their own species.
Cabbage mentioned chimps. I remember seeing a programme, possibly Chimp Diaries, where a troop of chimp went out to patrol their territory and heard a bordering troop nearby. They went on to attack them killing and eating one or two I think.

I'm sure the chimps were hunting monkeys rather than other chimps in the article and programme I watched but a quick look online shows you're right Hawkeye there certainly does seem to be a fair amount of evidence for chimp groups attacking and killing each other with some scientists speculating it may even be something akin to the human practice of making war - they even suggest that they do it for specific reasons such as seizing land or resources.

[Hawk_Eye]

I'm sure the chimps were hunting monkeys rather than other chimps in the article and programme I watched but a quick look online shows you're right Hawkeye there certainly does seem to be a fair amount of evidence for chimp groups attacking and killing each other with some scientists speculating it may even be something akin to the human practice of making war - they even suggest that they do it for specific reasons such as seizing land or resources.

Whatever programme it was I saw I think they gave similar reasons. I have also seen a similar programme to yours where they hunted monkeys. I wonder whether BBC Wildlife could do or has done an article on this subject, just out of interest.

[Deimos]

Another consideration in the "infanticide" discussion is when a new dominant male will kill young he did not father. Means of ensuring available resources go into keeping his genes surviving and being passed to future generations (which I guess is what it is all about). Social grouping and cooperation is still selfish at the end of the day.

Ian

[cabbage]

Another consideration in the "infanticide" discussion is when a new dominant male will kill young he did not father. Means of ensuring available resources go into keeping his genes surviving and being passed to future generations (which I guess is what it is all about). Social grouping and cooperation is still selfish at the end of the day.

Ian

I think this is essentially the strategy followed by male lions. I think its also how wolf packs behave, the dominant pair have offspring but prevent other members of the pack doing the same - I think I've read that a dominant female wolf will attack any subordinate that becomes pregnant, usually forcing a miscarraige. By doing this they ensure all the resources of the pack go towards raising their offspring (and their genes).

For any species the greatest source of competition for resources will always come from others of the same species - and for social groups it will come from members of the same social group. From a strictly evolutionary perspective then if a parent can get away with killing other infants of the same group it could be a good strategy. Likewise for many species, siblings killing each other whilst young is pretty common. A sibling is the ultimate source of competition. My brother for instance was always stealing my lego.

[Deimos]

Another consideration in the "infanticide" discussion is when a new dominant male will kill young he did not father. Means of ensuring available resources go into keeping his genes surviving and being passed to future generations (which I guess is what it is all about). Social grouping and cooperation is still selfish at the end of the day.

Ian

I think this is essentially the strategy followed by male lions. I think its also how wolf packs behave, the dominant pair have offspring but prevent other members of the pack doing the same - I think I've read that a dominant female wolf will attack any subordinate that becomes pregnant, usually forcing a miscarraige. By doing this they ensure all the resources of the pack go towards raising their offspring (and their genes).

And then it gets more complex ... when you start to consider "kin-altruism" (suicidal altruism); where behaviour resulting in an individual's death but allowing others who are genetically related to survive can actually help some of their genes to be passed on, although obviously not all and not directly. Saving two siblings/parents/children but die in the process is genetically "break even". Save more and as far as passing your genes on and you are on the beneficial side, save less (and die in the process) and you are below the line. And you can then do the maths for more distant relatives. So in packs where many individuals are genetically related, behaviour that results in the individual's death but saves the rest of the pack can work well as far as ensuring your genes get passed on. And then consider the case of monozygotic twins. And were does germline chimerism fit into all this (e.g. in Marmosets) ?

etc. etc. I guess it comes down to strategy.

Ian

[cabbage]

Another consideration in the "infanticide" discussion is when a new dominant male will kill young he did not father. Means of ensuring available resources go into keeping his genes surviving and being passed to future generations (which I guess is what it is all about). Social grouping and cooperation is still selfish at the end of the day.

Ian

I think this is essentially the strategy followed by male lions. I think its also how wolf packs behave, the dominant pair have offspring but prevent other members of the pack doing the same - I think I've read that a dominant female wolf will attack any subordinate that becomes pregnant, usually forcing a miscarraige. By doing this they ensure all the resources of the pack go towards raising their offspring (and their genes).

And then it gets more complex ... when you start to consider "kin-altruism" (suicidal altruism); where behaviour resulting in an individual's death but allowing others who are genetically related to survive can actually help some of their genes to be passed on, although obviously not all and not directly. Saving two siblings/parents/children but die in the process is genetically "break even". Save more and as far as passing your genes on and you are on the beneficial side, save less (and die in the process) and you are below the line. And you can then do the maths for more distant relatives. So in packs where many individuals are genetically related, behaviour that results in the individual's death but saves the rest of the pack can work well as far as ensuring your genes get passed on. And then consider the case of monozygotic twins. And were does germline chimerism fit into all this (e.g. in Marmosets) ?

etc. etc. I guess it comes down to strategy.

Ian

I love this sort of stuff, germline chimerism is a new one on me I'm off to research it

Kin altruism I'm more confident on I think the classic example of this is - in mammals at least - naked mole rats. Its a fascinating and elegant strategy and, once you get your head round it, it makes a lot of sense.

I've heard it given as an example as well as to why such things as 'heroism' and self sacrifice exist in human society - though I think its a bit contentious. Any group which contained a certain amount of people - but not too many! - prepared to give their lives for the group as a whole would have a better chance of survival than a group which didn't contain any of those individuals. The individual may die but his/her genes will go on in the group.