{"id":528,"date":"2009-09-04T13:47:40","date_gmt":"2009-09-04T01:47:40","guid":{"rendered":"https:\/\/blog.waikato.ac.nz\/bioblog\/2009\/09\/wait_until_you_can_see_the_whi\/"},"modified":"2009-09-04T13:47:40","modified_gmt":"2009-09-04T01:47:40","slug":"wait-until-you-can-see-the-whi","status":"publish","type":"post","link":"https:\/\/blog.waikato.ac.nz\/bioblog\/2009\/09\/wait-until-you-can-see-the-whi\/","title":{"rendered":"wait until you can see the whites of their eyes"},"content":{"rendered":"

I was in a schol bio tutorial the other day & one of the students asked a really intriguing question – one that I hadn’t really thought about before. Apparently the class had watched the series Walking with cavemen<\/i> a few weeks ago, & at some point (she couldn’t remember which species it was) the narrator said that this particular species was the first to have whites to their eyes. The student said, I was wondering what the significance of that is.  Do you have any ideas<\/i>?<\/p>\n

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And of course I said – no, I honestly haven’t got a clue. But I could offer an hypothesis, & try later to find out more. But first – I don’t know how the narrator (well, the people writing the script) could actually know if a particular species, one known only from reasonably scanty fossil evidence, had eyes like ours. And yes, our eyes are<\/i> different. If you look at any of the great apes, you’ll find that the whole of the visible part of the eye (both sclera & iris) is pigmented. Other animals may have a white sclera but (as for my puppy) normally all you see is the coloured parts of the eye. Ours, on the other hand, have that prominent while sclera surrounding the coloured iris. But things like that don’t fossilise, so it’s surely just conjecture to say that a particular species had what we’d regard as fully ‘human’ eyes…<\/p>\n

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Anyway, what about that hypothesis? Well, I suggested to the class that having that expanse of white around the iris really makes our eyes stand out. You can see which way someone’s looking, or if they’re surprised or startled (in which case your eyes often open wider, so that white ring would be even more obvious). Perhaps, I said, this is an adaptation that aids communication & social interaction. (Hard to cast deep & meaningful glances if the object of your attention can’t really be sure that you’re looking at them!) The class agreed that this might be a possibility & we left things at that.<\/p>\n

But now I’ve done a bit of research \ud83d\ude42 First up was a news report<\/a> that suggests that maybe I was thinking along the right lines: it describes research examining the effect of head & eye movements on redirecting the gaze of apes (gorillas, common chimpanzees, and bonobos) & 12- to 18-month-old human infants (Tomasello, Hare, Lehmann & Call, 2007). Tomasello & his colleagues noted that humans seem more likely than other primates to spend time in collaborative activities that see each individual keeping an eye (pardon the pun!) on what the other individuals are looking at – this may allow better coordination of their joint activity. They devised an experiment to see whether humans were in fact more likely than apes to follow the direction of someone’s gaze.<\/p>\n

Working first with the different apes, they used the following set of experimental conditions. One of the team (the ‘experimenter’) sat before one of the apes (the subject), and did one of the following:<\/p>\n