This is another recent paper from PNAS, and I’ll put the link in the screenshot (pdf here), but I’m not going to report on it in detail. Rather, this is an excuse to show a video that demonstrates the paper’s main point: while some animals can distinguish greater from smaller amounts of food using vision, elephants can do it using smell. This appears to be the first example of the use of olfaction in cognitive tasks by an animal. You might think dogs have a keen sense of smell, but they fail the smell test used in this paper.
The journal Science gives the video below as well as presenting a short popular summary of the paper.
To conduct the research, scientists presented six Asian elephants (Elephas maximus) at an educational sanctuary in Thailand with two opaque, locked buckets containing 11 different ratios of sunflower seeds, a favorite treat. The elephants could not see how many seeds each bucket contained, but they could smell the contents through small holes in the lids.
The animals chose the bucket with the greater quantity of food 59% to 82% of the time, the team reports today in the Proceedings of the National Academy of Sciences. (Even dogs, with their famed sense of smell, fail this test, other research has shown.)
And there’s a cool bit of stuff about olfactory receptor genes (OR genes), which I discuss in Why Evolution is True because we have many dead ones compared to our relatives. The presence of nonfunctional OR genes that are functional in our relatives can’t be explained by anything other than common ancestry, one of the tenets of evolutionary theory. Here’s more from Science:
The discovery makes sense, the scientists say, because elephants are known to have the highest number of genes associated with olfactory reception of any species (about 2000 versus dogs’ 811). They can distinguish between the scent of Maasai pastoralists and Kamba farmers, and rely on their sense of smell to navigate long distances to find food and water (up to 19.2 kilometers). The researchers hope their findings could help mitigate human-elephant conflicts in Asia and Africa, because wandering herds use odors to decide where to travel; enticing scents might help lure them away from agricultural fields, for instance.
I was surprised at elephants’ smelling ability even though they have those big trunks, as the trunks are used for many other things, like pulling down leaves and fruits. Humans have about 400 active OR genes, versus the 800 in dogs and 2000 in elephants. We also have another 400 inactive OR genes, showing evolution. (We’re a visual and auditory rather than an olfactory species, so the loss of smelling ability probably didn’t cost much.) In dolphins, as you might expect, the bulk of OR genes are inactive, because they have a different way of “smelling” underwater.
But enough didactic stuff. Watch two elephants pass the “smell test” (remember, they err between 18% and 41% of the time). I love the experimental setup, and hope that the investigators weren’t giving any “Clever Hans” signals!