- Animals of all sorts kill themselves.

- Animal suicides can teach us a lot about human suicides.

- For centuries people either denied animal suicides or took them as evidence of human-like intentions.

Whether it's a grieving dog, a depressed horse or even a whale mysteriously beaching itself, there is a long history of animals behaving suicidally, behavior that can help explain human suicide, says newly published research.

The idea that animals could actually be very good models for human suicide started to take root in the 20th century, said Edmund Ramsden, one of the authors of the study published in the latest issue of the journal Endeavour, along with Duncan Wilson of the University of Manchester.

"You begin to challenge the definition of suicide. The body and mind are so damaged by stress and so it leads to self destruction. It's not necessarily even a choice," Ramsden told Discovery News.

"It becomes reversed, in a sense," said Ramsden. Animal and human suicides are no longer seen as willful acts but as responses to conditions.

There are many stories of animal suicide dating back centuries. In 1845, for example, the Illustrated London News reported a "Singular Case of Suicide" involving a "fine, handsome and valuable black dog, of the Newfoundland species." The dog had for days been acting less lively than usual, but then was seen "to throw himself in the water and endeavor to sink by preserving perfect stillness of the legs and feet."

The dog was rescued and tied up. But as soon as he was released he entered the water again and tried to sink himself. This occurred several times until at last the dog appeared to tire and "by dint of keeping his head determinedly under water for a few minutes, succeeded at last in obtaining his object, for when taken out this time he was indeed dead."

Such anecdotes tend to reflect the values of the societies they are from, said Ramsden.

In the 19th century, animal suicides were often seen as acts of abuse, madness, love or loyalty -- the same causes then given for human suicides. In earlier times, such qualities weren't assigned, but animals were still used to help define suicide.

A Newfoundland dog. An 1845 article in a London newspaper describes the drowning suicide of a similar dog.Getty Images

"For (St.) Augustine and (Thomas) Aquinas it goes against natural law and so goes against God's law," Ramsden told Discovery News. They called on the lack of suicide in Nature as proof that people should not kill themselves.

But Aquinas couldn't have been more wrong, says psychologist Thomas Joiner of Florida State University and author of the newly-published book "Myths of Suicide."

"It's incredible how actually pervasive it is in nature," said Joiner. Organisms of all sorts are known to self-destruct in one way or another, usually in order to protect their relatives -- and so to save their genes.

"If you take the statement: 'My death will be worth more than my life,' that plays out in all sorts of organisms," said Joiner. "That calculation is the same, whether it's written in the genes or English."

Pea aphids, for instance, when threatened by a lady bug can explode themselves, scattering and protecting their brethren and sometimes even killing the lady bug. They are literally tiny suicide bombers, Joiner told Discovery News.

The big difference is that in modern humans that calculation can go wrong. There are some acts of suicide that do save lives. But most of the millions or so human suicides each year worldwide benefit no one, Joiner explained. They are acts that perhaps used to serve a purpose in early human societies, he said, but have lost their function in the modern world.

What that suicidal Newfoundland was telling us, then, is not so much that animals and humans think alike, but that it is, as Joiner said "...a fatal consequence of biologically-based and extremely serious illness."