(C) Daily Kos
This story was originally published by Daily Kos and is unaltered.
 . . . . . . . . . .



Top Comments: The Geosmin Molecule and Human Evolution [1]

['A Pagan In Arizona', 'Bill In Portland Maine']

Date: 2026-08-21  

Uploaded to DailyKos by Ed Tracey

Here at Top Comments we strive to nourish community by rounding up some of the site’s best, funniest, most informative commentary, and we depend on your help!! Here’s how to submit nominations in DK6: If you see a comment by another Kossack that deserves wider recognition, please send it either to topcomments at gmail dot com or via kosmail to topcomments- either search for user @topcomments, or click that link then click “send message”!) by 9:30pm Eastern for inclusion in that day’s diary. Please, please include a few words about why you sent it in as well as your user name (even if you think we know it already :-)), so we can credit you with the find! It’s especially helpful if you include a link to the comment you’re nominating… hover over the comment and you’ll see Share and Report options. Click Share, then choose ”copy url” and paste that into your message to us.

Structural formula of geosmin. Each unlabeled vertex is a carbon atom. Each carbon atom in this molecule bonds to four other atoms. Each line is a bond between atoms. As shorthand, most of the hydrogen atoms in this molecule are not explicitly drawn; For any canon atom explicitly depicted as having fewer than 4 bonds actually has the number of hydrogen atoms needed to satisfy that condition. By Calvero – self-made with ChemDraw., Public Domain, Link

I recently discovered the existence of the molecule geosmin, shown as a 3D model in the title image. Its chemical formula is C 12 H 22 O. An alternate structural formula is shown at the right. This molecule is produced by bacteria in soil when the soil becomes damp. It carries the scent of moist soil to us. You know that scent after a rain? That’s geosmin. The name of the compound comes from Greek for “smell of the earth.”

What’s unusual about this compound, in relation to humans, is how sensitive humans’ sense of smell is to this particular compound. We can detect its presence down to 400 parts per trillion. (That’s equivalent to all of $16,000 out of the recently reported national debt of $40 trillion.) Normally, we don’t think our sense of smell is all that sensitive, but for this particular compound, it is uncharacteristically sensitive. You might be able to guess why that should be: It helps us find water, a vital resource.

It was recently reported that humans went through an evolutionary bottleneck about 900,000 years ago in Africa. (Note that this claim is in dispute, but that there is genetic evidence that at least one significant population of humans surviving today went through this bottleneck event.) Due to a climate change event, the environment became cooler and drier, and it is estimated that the number of humans capable of reproduction dwindled to about 1,300. If the claim is correct, that suggests that 99% of human population was wiped out. In a situation where water was scarce, that extreme sensitivity to geosmin may have brought us through that bottleneck. (Let me be clear that this last sentence is pure speculation, but I still think it’s possible.) It’s interesting to consider that the pleasant smell of rain may have saved us from extinction.

On to the Comments:

From RosyFinch:

[END]
---
[1] Url: https://www.dailykos.com/stories/2026/8/21/800087814/community/top-comments-the-geosmin-molecule-and-human-evolution/

Published and (C) by Daily Kos
Content appears here under this condition or license: Site content may be used for any purpose without permission unless otherwise specified.

via Magical.Fish Gopher News Feeds:
gopher://magical.fish/1/feeds/news/dailykos/