Hey, the next episode of the History Channel’s series on evolution is coming up soon: Evolve: Sex. I don’t quite have the stamina to liveblog it tonight — I’m ready to fall asleep sitting down — but I’ll be tuned in and trying to watch it.

Last week, we watched Evolve: Eyes on the History Channel; tonight, shall we watch the next episode, Evolve: Guts, together? Tune in shortly!

A disgusting beginning: competitive eaters? Bleh. It’s a basic introduction to mammalian digestive physiology — I can tell we’re going to get lots of Big Vertebrate biology again.

They show a cool machine called Cloaca that simulates human digestion, with vats containing chemicals to act as the various chambers. They don’t bother to explain why this machine was built, but it is kind of weirdly interesting.

Once again, they openly say that the complexity of the digestive system evolved — that’s rather refreshing.

Yay! They go back to microorganisms 700 million years ago…for 30 seconds. Then we move on to Ediacaran organisms. The evidence shows that they weren’t photosynthetic, but were some kind of animal that had to have fed somehow, and probably were passive absorbers of drifting nutrients. They suggest that they were replaced by Cambrian organisms that had guts.

Jellyfish just have a sac, not a tube. Cambrian creatures had a more elaborate feeding system, allowing for sophisticated mobile predators, and we see an arms race. Nice animations of Anomalocaris all over the place!

Zip to the modern day: submersibles discover exotic deep sea worms that live on dead whale bones. They have no mouth or gut, so how do they eat bone? They were drilling in and bringing bacteria with them that broke down the bone, and then the worms absorbed the bacteria.

Hey, they mention bacteria, and talk about how digestive enzymes secreted by bacteria are predecessors, and are necessary for the extraction of food in our own guts.

They also mention fish and specialization of regions in the gut tube! More fish, please! But no, we’re going to go straight to tetrapods now, and the promise before the break is dinosaurs. Oh, well.

I’m really pining for more about the actual evolution of guts — and something about development. How can they talk about epithelial tubes without talking about development? Jumping to dinosaurs skips all the interesting stuff. Guts are done by the time you’ve got dinosaurs.

OK, dinosaurs. Yeah, yeah. They discuss gizzard stones and the relationship of dinosaurs to birds. Were dinosaurs warm-blooded? Their digestion was less croc-like and more bird like, determined by analyzing dinosaur coprolites, including T. rex droppings, which contain fragments of fossilized bone. They contain large quantities of bone, which suggests a croc-like eating pattern. But they also contains fragments of fossilized muscle tissue, which suggests that food passed through rapidly, like a bird. So it was a glutton that also had to eat frequently.

The K/T event meant that these big consumers all starved to death. The lead-in to the next section is all about snakes and mammals.

Snakes! Theyre going to talk about the evolution of feeding strategies (why not use cichlids, though? They’d be better). Oh…because you can show movies of snakes swallowing mice whole.

Nifty x-rays of poor mice dissolving in a snake’s gut.

Discussion of the ability of the snake to shut down its gut between meals. Microvilli lining the intestine actually contract while fasting, and increase in length when feeding.

20 million years ago, there was a widespread increase in grasslands that represented a new opportunity … but was hard to eat because much of it was bound up in cellulose. Ruminants evolved fermentation chambers. They show a surgically fistulated cow that allows researchers to get their hands right into a gut. They use bacteria to help break down tough plant material.

These adaptations promote the growth of herbivores…which leads to the evolution of predators.

Now it’s on to humans, of course. They suggest that maybe the key innovation in our ancestors wasn’t our brain, but guts: big-toothed, small-brained apes evolved into small-toothed, big-brained humans. A switch in diet to more meat, and the use of tools to ‘pre-digest’ food allowed us to have smaller guts. Cooking was another huge change that greatly improved the quality of the diet.

They measure the energy required by snakes to digest raw vs. cooked meat. Cooking reduces the cost of digestion by 12.5%. Human guts evolved to be more efficient, liberating more energy for the evolution of the brain.

OK, much like last week’s episode, this show’s strengths are also its weaknesses. The emphasis on charismatic megafauna may be great for catching the attention of casual viewers, but it leaves out all the important events in the evolution of these structures, and ends up emphasizing late refinements and details. Somehow, we need to get a documentary that brings up more molecules and development and the all-important teeny-tiny creatures, where the major innovations first appeared.

But still, I’m most impressed to see a television show that unapologetically discusses evolution as the only credible explanation for the appearance of these features.

Tonight, at 9 Central/10 Eastern, it’s time for the second episode in the History Channel’s series on evolution: Evolve – Guts.

It doesn’t just take willpower to survive. It takes guts–in the form of a digestive system that turns food into fuel. Look closely at the role guts have played in shaping some of Earth’s most successful animals: tyrannosaurs, snakes, cows, humans and others. Take a 575-million year journey that begins with the planet’s first multi-cellular organisms and ends at our dinner tables. Watch as live-action natural history sequences, CGI, epic docudrama, and experimental science help to illustrate our and our fellow species’ eternal struggle for survival on earth.

I think I’d rather hear more about the digestive systems of protists, Trichoplax, sponges, and cnidarians than T. rex again, but shall we watch it together as we did last week?

The warm-up act for this program was a dinosaur program called “Jurassic Fight Club”, which was loaded with CGI and lots of gratuitous razzle-dazzle — but I thought it was a hoot. It also had enthusiasatic scientists talking about how they figured out what had happened (although it does bug me that they treated some speculative stuff in the narrative as if it were factual). Most of the show was taken up with glitzy animations, but it was balanced with at least some discussion of the process of science, so I’ll give it a thumbs up.

Now to settle in for the story of the evolution of eyes…

Oooh: “the sparks of evolution are tiny, random changes called mutations”. I’m pleased that it jumps right in without compromise. It also promptly pushes the timeline back to 600 million years, and describes work done on jellyfish eyes. They show some very cool behavioral studies of how jellies respond to different wavelengths of light, illustrating why even simple animals would find light-sensing organs beneficial.

Teaser before the first commercial: trilobites. It looks they’re trying for a chronological approach.

The commercials are really annoying: Kinoki foot pad quackery and bigfoot. Bleh.

Now we get a quick summary of the Cambrian explosion — I saw an anomalocaris swim by. The first fossil eyes are from the Cambrian; compound eyes on arthropods. Modern insects are shown, explained as not descendants of trilobites, but probably share the same genes Good acknowledgment of the successful utility of dragonfly eyes.

Dang. Too little time spent on invertebrates — they’re already switching gears to focus on vertebrates.

Pikaia! Cool. Kinda nice that they’re setting up the vertebrate eye as an icon of evolution, and a kind of machine — good dig at ID. There’s also a nice simple animation of how an eye patch could form an eye cup, then an eye with a lens.

Yeah, they already leap into those sexy, glitzy dinosaurs. A little more time should be spent on those unsexy hagfish and lampreys, more interesting as transitional forms, but OK, most people wouldn’t find them as interesting as I would. They show Kent Stevens (UO! Yay!) work on identifying visual fields from dinosaur fossils, and discuss binocularity.

T. rex makes for good visuals, but is it really the best animal for discussing the evolution of vertebrate eyes? The innovations were all in place before the dinosaurs came on the scene!

Next lead-in: we’re about to learn about mammals and night vision.

Primitive mammals were largely nocturnal. So what are the special adaptations in the mammalian eye for night vision? Lots of isolated eyes in jars; the answer from comparative anatomy is that the size of the cornea is important. Cool: tarsiers have eyes that are bigger than their brains.

Another strategy: the tapetum, a reflective layer at the back of the eye. Nifty dissection of a big cat’s eye to show the structure.

Looks like the last 15 minutes of the program will be about human vision…

We lucky humans have color vision. Mammals radiated into numerous niches after the great extinction at the K/T boundary, and primates moved into the trees. Why did natural selection favor improved color vision in primates? Monkeys are shown to favor the youngest, tenderest leaves…which have color differences from old leaves.

Primates also have binocularity for better depth perception, an adaptation for living in trees. This gives them a narrower field of view, unfortunately. Birds of prey targeted these animals with limited vision, which made group living more advantageous for primates. They suggest that this would promote more social behavior and intelligence.

Summary: Not bad. The title is a bit of a misnomer, though, since only a little bit of it was about the evolution of eyes. A program more true to its title would have spent much more time on invertebrates, would have said more about the molecular underpinnings of vision, and would have concentrated on hagfish, lampreys, and teleosts among the vertebrates.

I know…dinosaurs and people are much more popular creatures, so the show compromised on the science for the sake of visual appeal. That’s an unfortunate reality of the conventions of TV programming, but it would have been nice to see them break out of that straitjacket, especially since the early part of the show on jellyfish was arresting and cool, showing that it can be done.

It was unabashedly pro-evolution, too, not giving a second to the silly stories we get from creationists. That’s a real plus, too.