Animals have been smelling for hundreds of millions of years, but the evolution of that sense is difficult to trace. You can’t ask an elephant to describe the fragrance of an acacia tree, for example, nor can you ask a lion if it gets the same feeling from a whiff of the same plant.

So scientists have to gather indirect clues to how different species use their noses. One way is to run simple tests on animals, seeing if they show an ability to tell different odors apart. Elephants, for example, can tell the difference between the smells of as many as 30 different members of their extended family.

Another way to track the evolution of smelling is to dissect the