Back in 1986 a biologist named Cindy Lee Van Dover was poking around the innards of shrimp from the bottom of the sea. They came from a hydrothermal vent in the Atlantic, where boiling, mineral-rich water came spewing up from cracks in the Earth’s crust and supported rich ecosystems of tube-worms, microbes, crabs, and other creatures. The animals that lived around these vents were generally blind, which wasn’t surprising considering that no sunlight could reach them. But Van Dover noticed that they had two flaps of tissue running along their backs that connected to nerves. Closer inspection revealed that the tissue was actually made of light-sensitive pigments and photoreceptors. What, Van Dover wondered, could these shrimp possibly be looking at. Dives to mid-ocean ridges later revealed that the vents produce a faint light of their own.
The New York Times, June 21, 2005
Jellyfish have traditionally been considered simple and primitive. When you gaze at one in an aquarium tank, it is not hard to see why.
Like its relatives the sea anemone and coral, the jellyfish looks like a no-frills animal. It has no head, no back or front, no left or right sides, no legs or fins. It has no heart. Its gut is a blind pouch rather than a tube, so its mouth must serve as its anus. Instead of a brain, it has a diffuse net of nerves.
A fish or a shrimp may move quickly in a determined swim; a jellyfish pulses lazily along.
Continue reading “Plain, Simple, Primitive? Not the Jellyfish”
I’ve got an article in today’s New York Times about jellyfish and their kin—known as cnidarians. Cnidarians look pretty simple, which helped earn them a reputation as simple and primitive compared to vertebrates like us, as well as insects, squid, and other creatures with heads and tails, eyes, and so on (known as bilaterians). But it turns out that a lot of the genes that map our complex anatomy are lurking in cnidarians, too. Scientists are now pondering what all that genetic complexity does for the cnidarians. They’re also using these findings to get a better idea of how the major groups of animals evolved between 600 and 500 million years ago.
In October 2004 Australian and Indonesian announced they had discovered a three-foot tall species of hominid, Homo floresiensis, that was still alive no earlier than18,000 years ago. As I’ve detailed in previous posts, this claim has inspired a lot of debate, much which revolves around whether the fossils, found on the Indonesian island of Flores do in fact represent a new species, or whether they were human pygmies. This week a new study was published in the journal Biology Letters (link to come) that puts this debate in the proper evolutionary frame. The paper is not about hominids, however, but about bats.
So let’s recap: It’s been almost eight months now since scientists announced the discovery of Homo floresiensis, the diminutive people that some claim belong to a new branch of hominid evolution and skeptics claim were just small humans. We seem to have entered a lull in the flow of new scientific information about Homo floresiensis. The last thing we heard from its discoverers came in March, when they published scans of the Homo floresiensis braincase, which bolstered their case that the skull they found didn’t happen to belong to someone with a birth defect. The skeptics have made various noises about evidence that the fossils are indeed pathological, and thus can’t be the basis for recognizing a new species. They have told reporters about their visits to pygmies who live near the fossil site on the Indonesian island of Flores. But they have yet to publish any of this in a scientific journal, where their claims could be put to some serious scrutiny. For example, you can’t refute the claim that the fossils are a separate hominid species by showing that living pygmies on Flores are very short. You also have to deal with the odd body proportions of Homo floresiensis, such as its long arms. Perhaps these are pathological too, but no one has gone on the scientific record yet.