Tuesday, July 29, 2008

Evolve - Eyes Live Bloggin'

I'm going to attempt to blog while watching "Evolve," the new History Channel show. This one is about the evolution of the eye.

So far, the previews have been pretty hyped up; the evolution of the eye is the fight for survival and of course, the eye is the weapon.

Intro about eye diversity. There's a really interesting description of eagle's eyes compared to human eyes focusing on the anatomy and how the anatomy of the eye changes vision. Not too bad. Then there's some talk of evolution as something that another thing does, specifically, "the eagle evolved" its eyes. Ouchie.

There's a segway with an animation timeline that displays evolution as linear.

We move on to the origin of eyes and use Polyorchis, the Bell Jelly, which has eye spots lining its base to talk about simple light receptors. The narrator describes an experiment where jellies are exposed to different light waves. The experiment is used to demonstrate how the eye aids in survival. In green light the jellyfish drift to bottom of tank, relaxed (the green light is the same wavelength as the ocean floor). In purple light the jellies become very active, pulsating (short wave light is higher energy - damaging to transparent organisms).


Narrator takes us back 500 million years ago (using that darn linear evolution animation). He describes the Cambrian explosion as an evolutionary arms race , the weapons being jaws, claws, body armor and eyes. In the Cambrian, we see the first evidence of compound eyes. There's some musing as to whether or not eyes were the reason for the explosion of life.

Little bit about insect eyes. Complex, compound eye. 29,000 lenses in Dragonfly eye. Poor focusing power, but rapid processing. Leave us with the idea that insect eyes and vertebrate eyes evolve from different ancestors.


Now we're talking about the vertebrate eye. It's a single lens camera of soft tissue. Someone talks about the vertebrate eye and it's history of being used to demonstrate the idea of an intelligent designer. There's a great animation showing Darwin's refutation of intelligent design of the eye, showing possible intermediate steps. I'm pretty impressed with this...it's not described in too much depth, but the average person could see it and get a pretty good idea of what's going on.

Okay...some dinosaurs and some really bad dino CGI. The narrator introduces Kent Stevens, who researches dinosaur vision. He made scale models and used lasers to plot the line of sight of both eyes. He then calculated degree of overlap (binocular field of vision). There's some talk about the advantages of binocular vision - mainly that it allows for judging depth and 3D vision. T. rex has 55 degrees overlap and therefore, like modern predators with similar overlap, probably hunted actively. Allosaurus had only 20 degrees of overlap and was therefore probably an ambush predators, like modern animals with lateral-facing eyes.

The narrator moves on to prey animals and how their eyes moved further and further apart over time, laterally. Rabbit eyes have 360 degree vision which allows them to see predators approaching from all angles, but see in 2 dimensions.


We begin with the evolution of night vision and how it may have aided in mammal survival during the Mesozoic. The narrator touches on the difference between eyes of nocturnals vs non-nocturnals; the cornea size. Larger corneas allow in more light. A really cool demonstration of Tarsier eyes and how they compare to human eyes.

Eyeshine. What is it? It seems that we won't ever know, but then tapetum lucidum, a layer of tissue behind the retina, is mentioned. Light bounces off the tapetum lucidum, giving a greater chance of absorption and causing some of the light to shine back out of the eye.


Color vision! Dinos out, mammals in. One group, the primates, settle into tree living. Somewhere along the line, there is an advantage to seeing more than just blue and green hues and the ability to see reds as well prevails. Why reds? Nate Dominy's research, which involves gathering the food of primates and using a spectrometer to analyze the colors of leaves that primates were eating, shows that red leaves composed most of the diets of tree-dwelling primates. Turns out red leaves are younger and more nutritious.

The narrator explains that binocular vision in primates, though they are not predators, comes in handy because the increased depth perception is compatible with arboreal living. Primates have 60 degrees binocular vision but that makes them vulnerable, so they live in groups to be safer, and therefore need larger brains?


So...I really liked the show. It was quite good. It had some fluff and there was a lot of hype, but I really feel that they did a good job of explaining why and how the eye evolved. To a layman, this show was neither too dumbed-down nor too technical.

What did you think?


Todd Oakley said...

Thanks for the summary! Here was my take as someone who studies eye evolution for a living.

Zach said...

What...what channel is this on? I need to catch the repeat!