Re: Did Neanderthals need glasses?

Tom,
	Interesting question.  The short answer is that most early humans 
probably saw well enough that they wouldn't need glasses if they were 
around today.  Now, why do I say that?
	Most physical characteristics fall into a normal, Guassian distribution.  
Refractive error does not. Refractive error is the mathematical amount of 
defocus that your eyes produce on your retina.  Refractive error is the 
biggest determinant in how well you see.  By the way, a positive refractive 
error means you're farsighted (hyperopic).  A negative refractive error 
means you're nearsighted (myopic).  
	Anyway, refractive error has a leptokurtic, not a normal, distribution. 
That means that a lot more people are near or at the mean (the mean is no 
refractive error in most studies) than we would expect from chance. In 
fact, the vast majority of people are either emmetropic (no refractive 
error, perfect vision) or slightly hyperopic.  If we look at macaque 
monkeys, the same thing holds true, although monkeys are a little more 
farsighted on average.  This distribution is already in place by somewhere 
between 18-36 months of age in humans.  We seem programmed to see well.  
Why and how this happens is a big, big debate that we won't get into.
	I think we have to assume that the distributions were much the same way 
for early humans.  Why, then, are so many people today in glasses?  The 
answer seems to be environment. Although nearsightedness does have a 
genetic basis, it correlates most strongly with amount of education a 
person has had.  This may explains why, at age 6, studies show very little 
refractive error in Western populations, but that myopia increases 
dramatically around the time kids start school.  
	In societies where people don't go to school (farming communities, 
aboriginal peoples), nearsightedness is pretty rare. Early humans didn't 
spend a lot of time reading, looking at chalkboards, watching TV, or 
surfing the net either.  They were probably checking out the horizon, 
looking for far off prey or predators.  So they probably didn't fall prey 
to the environmental factors that make so many people (myself included) 
nearsighted today.  Guess I shouldn't have read so many books.  Oh well.  
	As for hyperopia, most people can correct themselves by accommodating 
(increasing the power of their lenses, which we normally use for near 
vision).  This works for most hyperopes until they are in their thirties.  
Most early humans were probably dead by that age, and the ones that were 
still alive probably had other things to worry about than eyestrain.
	Of course, there are other factors that would have been important to 
early humans in vision besides whether they saw 20/20.  Consider peripheral 
vision, night vision sensitivity, motion sensitivity, color vision, etc., 
and there are definitely ways in which a person who wouldn't do as well on 
a simple vision test could have some powerful advantages over someone who 
"saw" a little better.  There is more to vision than just 20/20.

As always, 

Tom Stickel