Animal researchers have traditionally been apprehensive about attributing human emotions to other animals for fear of being anthropomorphic. But observations of animal behavior over the last few decades have made the attribution of deep emotion to some non-human animals more difficult to deny.

For instance, observations collected in 2006 and 2007 suggests that dolphins and whales, like with chimps, gorillas and elephants, may experience complex emotions once believed to be reserved for human beings: deep grief at the death of a loved one, according to a report by New Scientist.

That work comes from Joan Gonzalvo of the Tethys Research Institute, who since 2006 has been observing the bottlenose dolphin population of the Amvrakikos Gulf in the Mediterranean Sea. During one expedition, the researcher and his team witnessed a heartbreaking scene between a mother dolphin and her deceased newborn calf. The mother could be seen repeatedly lifting the corpse to the surface.

"This was repeated over and over again, sometimes frantically, during two days of observation," said Gonzalvo. "The mother never separated from her calf.... [She] seemed unable to accept the death."

Gonzalvo experienced a similar scene a year later, when he came across a pod of dolphins that appeared to be assisting a 3-month-old dolphin that was having difficulty swimming.

"The group appeared stressed, swimming erratically," he said. "Adults were trying to help the dying animal stay afloat, but it kept sinking."

"My hypothesis is that the sick animal was kept company and given support, and when it died the group had done their job. In this case they had already assumed death would eventually come — they were prepared."

In the first case, the mother dolphin seemed to be exhibiting grief at her calf's death, while in the second case the pod of dolphins seemed to show an understanding that death for their pod-mate was imminent. Taken together, the two cases suggest that the dolphins not only experience grief, but also that they may possess some of the higher level concepts entailed by the emotion. In other words, it seems as if they comprehend, and perhaps even contemplate, their own mortality.

Mourning behaviors transcend species

While interpretations of animal behavior are always suspect to some degree (Gonzalvo admits that his hypothesis is only speculative), his interpretation is backed by at least one recent study on cetacean neurology which showed that dolphins and whales possess specialized, human-like "spindle" neurons, which are the brain cells linked to empathy, grief and intuition in humans.

Gonzalvo isn't the only researcher to have observed such behavior. Ingrid Visser of the Orca Research Trust in Tutukaka, New Zealand, has observed bottlenose dolphins and orca whales carrying dead infants. She has also witnessed grieving behavior during pilot whale strandings.

"When one died the others would stop when passing by, as if to acknowledge or confirm that it was dead. If we tried to get them to move past without stopping, they would fight to go back to the dead animal," said Visser. "I do not know if they understand death but they do certainly appear to grieve — based on their behaviors."

Similar behavior has been observed in elephants, which have been known to stop and intently examine the bones of other elephants that have died. They only show interest in the remains of elephants, ignoring the bones of other species, which researchers have taken to show an understanding for what the skeletal remains represent.

Dramatic footage of chimpanzees grieving over the death of a loved one also offers compelling evidence for deep emotion in the great apes.

While there's not likely to be irrefutable evidence for the presence of higher emotion in other animals, examples such as these at least make the case for it.

"It's great to accumulate examples ... as more are gathered a clearer picture emerges," said elephant researcher Karen McComb of the University of Sussex.

Evidence continues to mount

To that end, a 2016 meta-analysis published in the May issue of the Journal of Mammalogy examined researchers' observations of mourning-like behavior in certain marine animals, from sperm whales to spinner dolphins. The researchers who compiled the analysis found numerous cases of the ocean animals engaging in unusual behavior, including an orca balancing a dead calf on her head to keep it above the surface of the water (similar to the dolphin Gonzalvo observed) and a spinner dolphin in the Red Sea pushing a dead body up to a boat and then swimming off once the humans aboard the boat placed the carcass on board.

Robin Baird, a co-author of the analysis, told National Geographic that orcas seem to "go through a period where they're experiencing the same kind of emotions you or I would when a loved one dies." This even includes examples of whales failing to eat or neglecting social bonds to instead focus on the dead companion. Sound familiar?

Editor's note: This story has been updated with new information since it was originally published in September 2011.