Now, two teams of scientists have managed to map the nose of a mouse. Using advanced genetic sequencing and imaging techniques, the researchers found that each of the 1,100 different types of olfactory receptors in the mouse nose occupied a distinct and predictable position, consistent from mouse to mouse.

— Read more in Scientists Unveil ‘Long Lost’ Map for Smell at The New York Times.

They found that Negritos, the hunter-gatherer group, had unusually well-preserved olfactory receptor genes. [...]

The findings suggest there is a strong evolutionary pressure to maintain these genes among Negritos compared with other populations, likely because smell plays a crucial role in foraging and hunting.

In addition, Negritos were more likely to carry genes associated with detecting earthy, fruity, and herbal smells, scents common in rainforest environments and often associated with edible plants and ripe fruit.

— Read more in Human sense of smell evolved with diets and lifestyle, genetic study suggests at Phys.org.

When a smell is associated with a threat, our sensitivity to it can also increase dramatically. In one study, Lundström and his colleagues showed that pairing a smell with an electric shock can make people detect that odour at much lower concentrations – a response that likely evolved to help humans react quickly to potential dangers, even when the smells are only faint. Similarly, the rotten eggs scent of hydrogen sulfide, a gas produced in sewage processing, can be perceived in concentrations as low as 0.5 parts per billion – an alarm bell for a gas that is lethal in higher concentrations.

— Read more in How bad smells affect your health at BBC.