We see so well because of snakes?
theatlantic.com
theatlantic.com
"The crux of Isbell’s Snake Detection Theory focuses on vision and is straightforward: 'Visual systems are more developed in those primates that have shared the longest evolutionary time with venomous snakes and least developed in those primates that have had no exposure at all to venomous snakes'."
There's also a very interesting and much longer review I just submitted: http://news.ycombinator.com/item?id=1195869
Edited: I see a lot of comments about snakes not preying on humans. But humans evolved over millions of years from much smaller primates. That's where Isbell thinks the evolutionary arms race took place. You could argue the reason snakes don't prey on humans is because our ancestors won that arms race.
Those same environments with higher density of vipers also play host to the widest variety of plant life. In many fruits and leaves, the differences between positive identification and edible vs. inedible have more to do with color and texture than scent.
Additionally, in a canopy environment fraught with the hazards and complexity of 3 dimensional navigation, and lack of a constant "ground scent-base", food source identification via sight would seem to be a more caloric-efficient approach. That's the strategy employed by most tropical birds and they have an even greater freedom of movement amongst the branches. It's also worth pointing out that exclusively ground-dwelling tropical birds such as Kiwi, Kakapo, Cassowary, and the Ocellated turkey all forage by scent and all have undergone reverse evolutionary trade-offs in visual acuity.
From the pop science summaries I thought she was full of crap. But the details are actually quite interesting, and I can see why she has other scientists excited.
Most (all?) animal senses have evolved firstly for finding and obtaining food.
From antelopes to bees, the spectral and polarization sensitivity (if any) of the eyes is perfectly matched to discriminate their primary food source against the background of their visual environment.
Predators evolved binocular vision (for distance estimation), and vergence tracking to estimate future prey pathing movement. In fact, amongst humans, the extremely wide margin in vergence tracking performance between the sexes is indicative of a very early specialization for hunting by men and gathering by women.
Evolving defensively against such an extremely rare event (no known extinct or extant species of snake even actively preyed against humans) would seem counter to the daily duty cycle demands of the human sensorium.
One of the interesting results is that women are better at short-range vergence skills (e.g. obscured fast facial recognition & foreground-background discrimination) while men are better overall and absolutely excel at long range pathing prediction.
So when there are two predatory species that try to avoid each other as much as possibly, how can there be such a strong effect by one to the other?
[edit] grammar fix. too early in the am
Wouldn't the dangers of uneven terrain, tripping, and falling be a better explanation of why we are good at looking down? Peripheral vision makes sense if you're also watching out for the family as you walk.
In programming terms, it's a narrowing funnel of accuracy. You start off vague but very very quick to catch the important stuff early, then you filter it better and better as you have time.
Her answer: snakes. “I cannot think of any other object in the lower visual field that would have been more difficult to see and more unforgiving if missed. The relationship between declarative pointing and the evolution of language is so strong, neurological and cognitive studies find, that the two are, to a degree, interchangeable. And so, Isbell avers, Genesis has it right: the snake made us human.”
I disagree with the assertion that only humans point declaratively. Other methods of "pointing" could include a variety of behaviors apparent in the animal kingdom: perked ears (cats), nose / "catching the scent" (dogs / esp. bloodhounds), flickering tongue (snake).
[edit] message for the downmodder: wtf?
None of these behaviours are naturally evolved communication methods, two are evolved traits that better adapt the animal to it's environment and the other is a learned behaviour.
If creationism ever compliments evolution it is purely by accident.
This is pure speculation. Who is to say that learned traits can or cannot evolve naturally, over time?
Besides, your use of "it's" is wrong.
An underlying assumption of the statement "pointing declaratively" is that there's some one or some thing to be declarative to (as in an audience, or partner, or fellow pack member). I liked the article, but it did go about assuming that humans are the only creatures who know how to be declarative.
We're probably more verbally declarative than any other species, but I highly doubt we're the only "declarative" species out there.
Right from the second sentence: "Coolly testing hypotheses and assessing evidence across an impressive range of disciplines[…]." Read aloud, that's a lot of 's's in an article about snakes. Fun!
Out of all species there are a lot of things humans do which are unique to humans. That doesn't mean such things evolved from snakes.