Obligatory Jennifer Wilbanks reference.
In your post #24 you suggested the question begging explanation that visible sclera were selected for because they were “attractive”. Der Trihs is saying that they may have been selected for because they are involved in social communication during courtship, which is quite a different matter, and much closer to what most of the other people in the thread have been saying than to what you said.
However, the highly developed human capacity for social communication is relevant to many other aspects of our success as a species apart from courtship - it enables all sorts of advantageous co-operative behavior - and there is much evidence that the human ability and strong inclination (which emerges in early infancy) to observe the direction of other people’s gaze is a very important factor underpinning that capacity.
Cats are not co-operative hunters, though, and are not particularly social. Your point might apply to dogs, however, or even to more social types of cats, such as lions. It might be interesting to look into whether such animals have the same sort of bias toward looking at one another’s ears that humans have toward looking at one another’s eyes.
I think it would be more accurate to say that don’t necessarily like each other very much. But cats living together under one roof definitely have nonvocal cues with which they communicate among themselves. What I observe right now, with regard to our latest addition to the family, is the new cat and Mia sorting out their territories and so forth.
Oh, I never told anyone about Suzie, did I? I’ll post pictures sometime.
I really don’t think it’s a different matter – he just focused on one element of attraction. Eye contact is a major part of attraction. My point was that the sexual selection angle makes more sense than the survival one, and that was an example of why this could be.
Anyway, I can figure out whether a dog or cat is looking at me pretty easily, despite their lack of obvious sclera.
Well, if what you say regarding evolution has any value, then we should be thanking our stars/Darwin that we have smaller eyes that we have lousier vision than the Neanderthals. Or that we see better with less brain. Or some such shit. (Athough the sclera’s component in their demise is not indicated. But still, we got to be be good-lookin’…)
Regarding neoteny, if in invoking it you imply its presence as a marker for inducing affection, this guy and this guy may argue differently. (In fact, this guy consciously ended his evolutionary potential years before he died.)
All of which brings up sanpaku, and how much fun you can have wasting time over it.
Yesterday’s VSauce touched on this. The video is ostensibly about why we kiss but drifts into this subject. Skip ahead to 4:30.
From the linked article:
That is utter bollocks. There is absolutely no reason why eyeball size should be correlated with the amount or proportion of the brain devoted to visual processing.
Guy, three points.
(1) I don’t see lions as group hunters. The telly videos almost always show a single female
lion taking down the prey alone, who is then joined quickly by the other females.
It makes sense for the best and fastest female to catch the meal so that the young, the lame
and the lazy don’t have to waste their diminishing calories.
(2) The sexual selection rather then the survival selection for visible sclera may by just
as significant. Back in the day, I learned that a female whom I caught looking at me twice
would be approachable at least for conversation. Smiling is a cue for chat but it is not
always the better cue.
(3) “calls” among group hunters? I don’t think so. Any noise or vocal signal might alert
the prey to danger. The exception would be a very large group of hunters that is flushing
a large beast or a small number of beasts.
However, I am sure your televisual researches, and insights into what “makes sense”, will lead science to reconsider its hasty conclusions on this matter.
OK David, then you’d better go tell hunters in general – and lions – that they’re all doing it wrong, haha.
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Watch this: http://www.youtube.com/watch?v=vRs3OjCrJYk
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I’ve been saying all along that sexual selection makes a lot more sense than survival-based selection in this case. I don’t see this as being important to survival.
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Hunters have probably imitated the sounds of animals (a.k.a. “calls”) while hunting for many thousands of years. It could be either to attract a certain prey, or to send a cue to other hunters (e.g. by imitating a harmless animal that wouldn’t alarm the prey). Example: Plains Indians - Wikipedia
And, once the trap is set, or the prey is already being chased, just yelling will work quite nicely (much, much more useful than trying to figure out where all the hunters are looking based on their sclera… looking at the directions their heads are facing ought to do just fine).
Agreed. The hypothesis also ignores that Neandertal brains were not only larger than those of modern humans, but *much *larger than those of their contemporaneous Homo sapiens. Size isn’t everything when it comes to brains, but it would seem Neandertals had plenty of brain to spare, even if, for some reason, more of it was devoted to visual processing.
Thank you for the warning, I’m sure I could scroll down a bit further because of it.
Well, actually, most of our brains are devoted to visual processing (more than to any other function, anyway). However, the fact is that we have absolutely no idea how functions were apportioned in Neanderthal brains (beyond the reasonable assumption that they did not differ all that much from ours), and almost certainly have no way of ever finding out. Certainly the size of their eyeballs is not relevant evidence. A bigger eyeball does not even necessarily imply more receptor cells in the retina, let alone how much brainpower might be devoted to visual processing.
The article says “Studies on primates have shown that eye size is proportional to the amount of brain space devoted to visual processing. So the researchers made the assumption that this would be true of Neanderthals.”
Is this not correct?
I find it hard to believe. Look at the Tarsier, a small primate with huge eyes (not the only one either). Indeed, its eye is as big or bigger than its whole brain.
It may be true that there is a rough and ready, on-the-whole, correlation between primate eye size and the proportion of the brain devoted to vision, but I do not believe it could be anything like sufficiently regular and exceptionless to support the inference that is being drawn. There are all sorts of factors that will influence the proportion of the brain devoted to visual processing, and most of them have nothing to do even with the number of receptors in the eye, which, as I pointed out in my post above, itself has little to do with actual eye size. Some of the relevant factors don’t even have to do with vision! If an animal has very good fine motor control in its fingers (as, for instance, humans do) this would probably mean that it would need a fairly large brain region devoted to motor control of the fingers, and that would mean that the proportion (although perhaps not the actual amount) of the brain devoted to vision would be smaller.
Even within our own species, there are some huge differences between individuals in the sizes of visual areas of the brain. Some people, for instance, have a primary visual cortex about two-and-a-half times the size of some other people’s. (AFAIK we really have very little idea why, or what effect, if any, this has on the people’s actual visual abilities.) In the light of this level of variability even within a species, let alone all the various factors that might influence both the actual and proportionate sizes of visual areas in different species, the idea that you could at all reliably infer the proportional size of a Neanderthal’s visual areas from its eyeball size is ludicrous.
True. I think this probably illustrates the principle that “correlation does not imply causation.” Primitive animals tend to devote larger proportions of their brains to visual processing. It just so happens that the most primitive primates (e.g. tarsiers and lorises) are nocturnal, and therefore have large eyes. There’s really no direct connection between large eyes and a relatively larger visual processing area in that situation, that I can see.
It’s also hard to look at a Neandertal and a tarsier and think, “yeah, those two are comparable.”
Not “or”, “and”. If a trait helps you survive but prevents or inhibits you from producing offspring, it won’t be selected for.
Their “contemporaneous H. sapiens” were modern humans. Modern humans and Neanderthals evolved at about the same time.
Even if you are distinguishing, as some paleo-anthroploigst do, between so-called “anatomically modern humans” and “us”, there are no significant anatomical differences between the two populations-- hence the name for the former.
Picture of Molly clearly showing the white of her eye.
