Most mammals have poor eyesight. But they supply this drawback with other sensory organs, mainly with sense of smell. Animals use smell for choosing a partner, a victim, for finding their cubs and parents. They also mark their territory with smelly substances. Animals are able to distinguish their fellows as well as other species. Sense of smell allows them finding the exact smell in a complex mix of various odors.
 

Some animals dwell alongside with us, so studying them is not kind of idle curiosity. Grey rats are the example. We rarely see them and are hardly able to tell one from another. As for rats, the research showed that they do that easily. Scientists from RAS Severtsov Institute of Evolution and Ecology Problems have tested whether rats remember people or recognize their smell without any special training. The experiments were conducted on grey rats, 2-8 generations of wild rat offsprings. First the scientists have recorded smells of 14 people aged from 20 to 40 years (6 men and 8 women), whom rats have never met before. For this purpose they out a 10x12 cm piece of filter paper on the volunteer’s wrist or stomach. After the paper was cut into pieces stored in aluminum foil at room temperature. The researchers put the rat in a separate cage, where it was able to nose the smelly paper for 15-20 seconds. The paper was hanging on the wall at the height of 15-20 cm to make the rat reach it. Not every rat has showed its interest in this paper. Those who didn’t were out of further experiments. Those who decided to nose the paper were put into a Y-shaped labyrinth with a paper smelling familiar in the one arm and unknown smell in another. The labyrinth was very small, 10x10x25 cm. The rat has entered its arms and nosed the samples.
 

The experiment showed that grey rats definitely distinguished between smells of six men. They nosed the familiar papers twice as long as they did with unknown smells (about two seconds). They behaved vice versa when the smell was female. They took less time to nose familiar papers (1.6 and 4.2 seconds respectively). According to the authors, such difference in exploring familiar and unknown smells of people of different genders shows that grey rats include gender information in human smell picture created in their brains.
 

Grey rats are known for spending less time for nosing their own females rather than males. “Gender smell” is evidently common for some species, may be even for all mammals. But some animals have lost the ability to recognize it. Not only half-wild grey rats have taken part in the experiment, but also laboratory white rats, multicoloured rats, nonpedigree and line rats were involved. They turned out to fail distinguishing between people.
 

The scientists believe grey rats can be used for identifying people according their smell like working dogs do. The animals can get special training in order to show correct results. Further we will have working rats instead of working dogs.