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An elephant's trunk is not only long, it is packed with five times more smell receptors than humans.

And now research has found that the African elephants have the greatest sense of smell among mammals - even beating dogs including the bloodhound renowned for its sniffing ability.

Humans were found to have the worst sense of smell across the species studied.

Researchers studied genes of 13 mammals. It found African elephants (pictured) have the greatest sense of smell, while humans were found to have the worst. According to the researchers, the African elephant can detect water from miles away and use their olfactory ability to detect predators at a distance

According to the researchers, the African elephant can detect water from miles away and use their olfactory ability to detect predators at a distance, find food or a mate.

The study, published in the journal Genome Research, examined the olfactory receptor (OR) range in 13 mammalian species.

These included horses, rabbits, guinea pigs, cows, rodents and chimpanzees.

They found the African elephant has the largest number of OR genes ever characterised.

To characterise the olfactory capabilities of different mammals, researchers examined genome sequences from 13 placental mammals and identified over 10,000 OR genes in total.

The repertoire of OR genes found in any given species was highly unique - only three OR genes were shared and evolutionarily conserved amongst all 13 mammals.

Yet, the African elephant had the most extensive olfactory repertoire, with almost 2,000 OR genes.

Dr Yoshihito Niimura of Tokyo Medical and Dental University said: 'The functions of these genes are not well known, but they are likely important for the living environment of African elephants.

'Apparently, an elephant's nose is not only long but also superior.'

By contrast humans, along with our primate relatives, have much fewer numbers of OR genes compared to all other species examined, possibly because we rely less on smell as our sight improved.

To characterise the olfactory capabilities of different mammals, researchers examined genome sequences. The repertoire of OR genes found in any given species was unique - only three OR genes were shared among all 13 mammals. Yet, the African elephant (pictured) had the most extensive range, with almost 2,000

The authors traced the evolutionary histories of OR genes using a novel computational tool to deduce ancestral genes, and then examined their duplication or loss in each species.

Some lineages of OR genes have greatly expanded in a given species, such as an ancestral gene that has duplicated in elephants.

This generated 84 distinct genes - humans and other primates only have one copy - while other OR gene lineages are completely lost.

Each species' unique olfactory repertoire, resulting from hundreds of gene duplications and deletions during evolution, highlighted the molecular basis for differences in olfaction across organisms.

Dr Niimura said: '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.'