Blog Rating

Selected Books by Edmund Blair Bolles

  • Galileo's Commandment: 2500 Years of Great Science Writing
  • The Ice Finders: How a Poet, a Professor, and a Politician Discovered the Ice Age
  • Einstein Defiant: Genius vs Genius in the Quantum Revolution

« What I've Learned About Language | Main | Speakers, Listeners, and their Common Ground »


Gordon Worley

I find your argument about gateways that can't be passed back through highly suspicious. It's tempting to think that an adaptation is so useful that it can't be evolved away, but really I think a better metaphor here is that of momentum. For example, symmetry in organisms evolved early on, so in order to remove symmetry requires either developing symmetrically and then activating additional genes to skew the symmetry (cf. the flounder) or following a path of successive adaptations that peals away the functions of various genes to eventually remove symmetric body development. Symmetry is an adaptation that has so much momentum, though, that to the best of my knowledge the latter has not happened, and if it has was likely near the point that symmetry was introduced.

As for your gateways, I'm not sure I would consider any of these particularly high momentum. Full bipedalism is a complex adaptation made up of many smaller adaptations, hence it would be harder to evolve out of but still possible (cf. dinosaurs, where this transition happened a couple times). Similarly, hairiness could be evolved again, given the right conditions and enough time, where sweating was less useful than a fur coat. As for the others, evolving out of them might require an event which would cause extinction first, but it would still be theoretically possible. So other than the first two I agree with you in spirit, if not in the details.


After 1 y 2, there is a third anatomical change. Human beings and only human beings (at least amongst the species alive nowadays) possess the ‘white of the eye’. (Cf. Kobayashi & Koshima, 2001)
BLOGGER: Yes, that's a notable feature of humans, but that is the kind of change that could easily be reversed if need be.


Well, the whole notion of "reverting" through these evolutionary doors is a kind of counterfactual imagining, which may have some heuristic interest, but it is more in the line of evolutionary studies to explain actual historical facts, rather than hypothetical or improbable ones. Therefore, I prefer to take the post's multiangled explanation on what makes us human (there must be more things besides) and say that I won't leave any of them out, though I might list them from top to bottom. Humanity has somewhat fuzzy limits, but the ability to use language, along with having a human shape, seem to head the list. Keep them all, though, because leaving one of them out would change all the others to a greater or lesser extent.

The comments to this entry are closed.

Bookmark and Share

Your email address:

Powered by FeedBlitz

Visitor Data

Blog powered by Typepad