[nudephil (OP)]

Gabriel asks:

Is there any observable evidence of suicide in animals? If there is, could it help in our understanding of it in humans?

Can anyone help out?

[evan_au]

Is there any observable evidence of suicide in animals?

I have heard of species of octopus where the female lays eggs, and then spends the remainder of her life tending them, not even eating. That is close to suicide...

[Bored chemist]

To have suicide you need to have "sui"- the Latin for self.
It's, at best, questionable that most animals know that they exist.
Things like the mirror test, while flawed, suggest that most animals can't recognise their own existence.
https://en.wikipedia.org/wiki/Mirror_test

If an animal doesn't know it exists then it certainly can't understand its own death.
And it is, therefore, unable to kill the "itself" that it doesn't recognise.

So, for example, a bee that stings you (to defend the hive) and consequently dies, not only didn't know that it would die, it never knew it was alive.

[alancalverd]

Few other animals have the ability to actively kill themselves (as distinct from starving or surrendering to a predator). Indeed it is quite difficult for a naked human to commit suicide other than by jumping off a cliff,  and even that is not available in East Anglia or our native savannah, and doesn't always work - you need a cliff with an overhang and at least 50 ft clear drop to flat, solid rock. Anything less may result in some broken bones and possibly kidney rupture but it's not obviously lethal unless you have seen it happen by accident.

Whilst you can't club yourself to death with a stone, you might slash your wrists with a sharp flint. You wouldn't know it was lethal  unless you had seen or heard of some other animal bleeding out from a cut, and we have no evidence of other species making knife-like tools: you need  at least an apelike thumb. 

Interestingly, this leads to the second distinction between homo sapiens and all other extant species: creating the means to kill itself.

[Bored chemist]

Anything less may result in some broken bones and possibly kidney rupture but it's not obviously lethal

For anything other than humans, that's lethal- slowly and painfully, but pretty reliably lethal.

unless you had seen or heard of some other animal bleeding out from a cut,

i.e. you are not actually blind.

we have no evidence of other species making knife-like tools: you need  at least an apelike thumb. 

or a cat/ dog/ rabbit like tooth
(Rabbits occasionally have the misfortune to kill themselves by losing an upper incisor. The lower one keeps growing- with nothing to wear it down- and eventually pierces the brain.)

Interestingly, this leads to the second distinction between homo sapiens and all other extant species: creating the means to kill itself.

An option that isn't open to rabbits is deadly nightshade- they happen to be substantially immune to atropine.
But there are plenty of other toxic plants (etc) out there. That puts paid to

Indeed it is quite difficult for a naked human to commit suicide other than by jumping off a cliff

And any land creature with enough determination just needs to swim to the bottom of the river and breathe in.

[alancalverd]

The underlying point is that suicide, as distinct from accidental death, depends on foreknowledge of the lethality of your chosen technique. Humans are exceptionally adept at recording and promulgating such knowledge. Indeed one of our distinguishing features is the desire and ability to write down anything that is too trivial to remember. 

You might also usefully distinguish between self-neglect (sick dogs and cats tend to go off their food, even when it is prepared and presented to them, and thus hasten their demise) and actively seeking a lethal device or substance.

[Bored chemist]

Indeed one of our distinguishing features is the desire and ability to write down anything that is too trivial to remember. 

Any time you want to stop, feel free.

[alancalverd]

Not only an absence of evidence of suicide in other species, but positive evidence of psychic avoidance of death.

My garden has always played host to squirrels, pigeons and pheasants, which amused the dog and did a little damage to my fruit and nut trees and bushes. The dog died a few months ago and the invaders became bolder, appearing all day and every day, strutting about as if they owned the place, and eating every berry and nut as soon as it ripened. 

I bought an air rifle a week ago. I haven't taken it into the garden, or even waved it near a window, but I haven't seen a single squirrel, pigeon or pheasant from the moment I brought it home. Can they read my mind, or smell gun oil at 50 yards?