A new examination of the olfactory receptor (OR) genetic repertoire in 13 mammalian species found African elephants have the largest number of OR genes ever characterized.

These elephants have twice as many "smelling" genes as dogs as and five times more than humans, Cold Spring Harbor Laboratory reported.

The findings were published today in the journal Genome Research.

The researchers examined the genome sequences of 13 placental mammals and pinpointed over 10,000 OR genes. Only three OR genes were found to be shared between all 13 mammals looked at in the study. African elephants proved to have the most extensive "olfactory repertoire," possessing almost 2,000 olfactory genes.

"The functions of these genes are not well known, but they are likely important for the living environment of African elephants," author Yoshihito Niimura said. "Apparently, an elephant's nose is not only long but also superior."

Humans and primates have significantly fewer OR genes when compared with the other species looked at in the study. This may because through time humans have relied less on scent and more on vision for understanding and interacting with the world around us.

To make their findings the research team traced history of OR genes using a "novel computational tool." This tool allowed them to deduce ancestral genes and look at how they were duplicated or lost in each species. Some OR genes in African elephants were found to have duplicated, creating 84 distinct genes. Each species had a distinct olfactory repertoire made up of hundreds of gene duplications and deletions throughout the generations. The findings highlight the "molecular basis for differences in olfaction across organisms."

"Comparison of the repertoires of OR genes among mammals lets us know the commonalities and differences of olfactory perception, deepening our understanding of the sense of smell in humans," Niimura said.