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From a story about Richard Feynman:

Then I looked at the bookshelf and said, "Those books you haven't looked at for a while, right? This time, when I go out, take one book off the shelf, and just open it--that's all--and close it again; then put it back."

So I went out again, she took a book, opened it and closed it, and put it back. I came in--and nothing to it! It was easy. You just smell the books. It's hard to explain, because we're not used to saying things about it. You put each book up to your nose and sniff a few times, and you can tell. It's very different. A book that's been standing there a while has a dry uninteresting kind of smell. But when a hand has touched it, there's a dampness and a smell that's very distinct

Is this true?

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    It's easier than picking a vault's lock in Los Alamos – Dr. belisarius Apr 11 '11 at 15:14
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    I don't have evidence, but try it - when you open a book which hasn't been looked at for a while you let air get to it. Makes perfect sense that that will allow dust and other particles to come out, and for some of the moisture in the air to get at the pages. Haven't tried Los Alamos yet @belisarius :-) – Rory Alsop Apr 11 '11 at 18:58
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    Out of curiosity, was "she" wearing perfume? – oosterwal Apr 11 '11 at 20:01
  • Might be one of those cases where there's another, simple, trick to it, but to make it more interesting you claim it's something more subtle. :) – Lagerbaer Apr 11 '11 at 22:14
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    @David I think it does make a difference. Paper decays and the act of opening a book will probably scatter decayed paper molecules. Given that only very few molecules are needed to trigger our sense of smell this seems a plausible cause. – Konrad Rudolph Apr 12 '11 at 12:16
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Firstly, we know that the mechanism exists for this to be achieved: dogs can already do this and can distinguish which and where human scents have been left.

In the case with Feynman he is claiming a similar mechanism, getting people to touch books that haven't been touched in a while so there is no residual scent and being able to find which book has been touched by comparing a person's scent to a scent left on a particular book. He has a slightly easier job to a dog that is picking up the scent of a stranger running through the bush.

I also have other anecdotes on the net where people have claimed Richard continued to do this as a party trick to non-believers, so it appears it was not a one-off which he refused to do again.

Years later, when Feynman was first at Caltech, he went to a party at Professor Bacher's house. He was talking to a group of people from Caltech when the story of smelling the bottles came up. Nobody believed a word of it. So, Feynman decided to perform the experiment again. He left the room and had three people touch three different books to see if he could identify who touched which book. He came back, smelled everyone's hands, and then smelled the books. He found the three books correctly and got one person wrong. Yet, the people still did not believe him.

There is this research paper (extract only) which indicates smells can be picked up between humans, but there results were only better in chance between relatives:

The basis of olfactory signatures mediating human kin recognition was investigated in two experiments. The odors of mothers and offspring were correctly matched (by subjects unfamiliar with the stimulus individuals) at a greater than chance frequency. In contrast, subjects were not able reliably to match the odors of husbands and wives. These data support the hypotheses that characteristic individuals odors are genetically mediated and that kin recognition should be facilitated by the similarity of such familiar odors among close relatives.

The only other evidence I could find of it being possible is this passage from Darwin's "Descent of Man and Selection in Relation to Sex":

“(36. The account given by Humboldt of the power of smell possessed by the natives of South America is well known, and has been confirmed by others. M. Houzeau ('Etudes sur les Facultes Mentales,' etc., tom. i. 1872, p. 91) asserts that he repeatedly made experiments, and proved that Negroes and Indians could recognise persons in the dark by their odour.”

Note this article seems to go into Olfactory Perception in excrutiating detail, if you want go through it in fine detail I suggest this would be the place to do it.

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