Question 1

How many smell genes do humans have and why are half of them dead?

Accepted Answer

Humans carry roughly 800 olfactory receptor genes, but about half are non-functional pseudogenes, disabled by mutation over evolutionary time. This left around 400 working receptors, which is still an enormous repertoire capable of distinguishing a vast range of odors.

Question 2

Is the human sense of smell actually weak?

Accepted Answer

No. The idea traces to anatomist Paul Broca in 1879, who judged the human olfactory bulb small relative to the brain and assumed poor smelling. Later research showed the bulb is normal in absolute neuron count, and humans out-smell dogs on certain molecules.

Question 3

Can humans track a scent trail like a dog?

Accepted Answer

Yes. In a 2007 Berkeley study, blindfolded participants on all fours successfully followed a chocolate-scented trail across grass using only smell, and they improved with practice, showing the human nose can track odors in stereo.

olfaction

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The Ruin That Wasn't: How Science Slandered the Human Nose