Elephants have the longest noses on the planet, so it makes sense that they have best sense of smell. Now scientists at the University of Tokyo have proved they at least have the potential.
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With some 2,000 genes coding for olfactory receptors, elephant genomes contain more genes for "smell bulbs" than any other species. By the criteria of number of genes, the beasts potentially smell five times better than people do, Japanese scientists have found. Humans have abut 400 genes for olfactory receptors.
Yoshihito Niimura of the department of applied biological chemistry examined 13 mammals and the elephant trounced the lot. The study, done on African elephants, found they have almost 2,000 different types of smell genes, more than twice the number in the most sensitive of dogs, says Niimura, one of the authors of the study published last month in Genome Research.
Let us now distinguish between having a gene and having a characteristic. You can have a gene, but it may not be expressed at all, or may be expressed weakly. For instance, you may have genes for brown eyes and blue eyes but (probably) your eyes will be a single color.
So, our elephants may have the most genes but that doesn't mean they're superior at smelling, just that they could be.
Previous studies done on Asian elephants did find extremely keen olfactory talent, as reported by a team headed by Alisa Rizvanovic in the journal Chemical Senses in 2012. The study, done admittedly on just two elephants, found with the help of food rewards that the beasts "performed at least as well as mice and clearly better than human subjects, squirrel monkeys, pigtail macaques, South African fur seals, and honeybees."
That team concluded that the elephants' extraordinary olfactory ability wasn't a function of the relative or absolute size of their olfactory bulbs. They did find a positive correlation with the number of functional olfactory receptor genes, which are expressed in the skin cells of the elephant's trunk.
Oddly, only three olfactory receptor genes were found to be shared by all 13 mammals. "Common genes have been preserved throughout the evolutionary process and we think that these hold important functions for all types of animals," says Niimura.
Genes specific to an animal probably developed to help it in its specific environment, he adds. And it turns out that elephants can distinguish between very similar scent molecules, which we can't. They can also tell each other apart by the smell of their pee. We can't do that either.