Friday, October 14, 2005

This article is kinda interesting:

SYDNEY (AFP) - Australian scientists have revived a project to try to bring an extinct animal, the fabled Tasmanian tiger, back to life, the team leader said.

I'm not sure that's even possible, actually. A while ago I read What Does a Martian Look Like?, an excellent book on what extraterrestrial life might look like and how it might be adapted to its world. Near the beginning of the book (around page 40, if Amazon can be trusted), the authors begin railing against Jurassic Park's idea that we could clone dinosaurs just from having samples of their DNA. Again trusting Amazon, since I don't have a copy with me, I'll try to excerpt some of the key passages and hope that I don't get sued. After a brief summary of Jurassic Park's premise, they write:

The scientific errors, unfortunately, are gross. In order to make a dinosaur, even nature needs more than its DNA sequence. In particular, it needs a female dinosaur to set the developing egg off on the correct trajectory. This 'dinosaur-and-egg' problem implies that you can't make a dinosaur unless you've already got one, in which case (give or take a male as well) you don't need to sequence ancient DNA in amber.

After this they unabashedly "rid[e] one of [their] scientific hobbyhorses"--the myth that once you know a creature's genome, you understand everything about it. After ranting for the better part of a paragraph (they do that a lot), they turn back to Jurassic Park:

This is the belief that lies at the core of Jurassic Park: that the genetic 'blueprint' for the organism determines everything about it. However, organisms are far more complicated than just a 'message' written in DNA.

We don't want to rehearse the biological arguments at any length, because we've already discussed them in The Collapse of Chaos, Figments of Reality, and The Science of Discworld--but the list of things that affect how an organism develops, but aren't DNA, is enormous. Parents often supply 'privilege'--extra food, such as yolk in an egg or milk. The example of the anglerfish, already mentioned, is instructive: here the fish's DNA does not even tell it which sex it should be....

Let's take this point one step further. All vertebrates start much the same: the embryos are very similar at what is called the phylotypic stage (stage typical of the phylum): all annelid worms look similar at their phylotypic stage, as do all gastropod molluscs (snails). Very different eggs (think of chicken egg, mammal egg, frog-spawn, caviar among vertebrates) all converge on to the phylotypic stage, and the strange thing is that they don't need their genetic instructions to do it. The egg architecture, plus a suite of clever molecules called informosomes copied from the mother's genetics, guides the pre-phyletic embryo to its phylum-typical shape, with its nuclei in lots of different kinds of cells. These different cells call up a different developmental programme from each of their nuclei, so that different genes are expressed in liver, kidney, nervous system and skin. In a very real sense, vertebrates are vertebrate because their mothers were: they made eggs that developed into vertebrate phylotypic embryos, which then read out their genes in the characteristic vertebrate way.

Because of this two-stage development, it is much easier to have a well-controlled passage of information: think of the egg as the tape-player, the chromosomal DNA information as the tape, which has on it instructions for making the ovary that makes eggs--tape-players--of the appropriate kind. That rather destroys the background 'science' of Jurassic Park, because it suggests that the tape player evolves as well as the DNA type. Ostrich eggs, and a bit of frog DNA to fill in the tape, just won't work. Nature agrees: rat nuclei (complete good-condition nuclei, not DNA that's been through a mosquito gut and then been bombarded by cosmic rays for 70 million years [--does that mean we'd get dinosaurs that could turn invisible? or stretch?] ...) won't develop properly in mouse eggs, and vice versa. And rat and mouse are a lot closer together than ostriches and tyrannosaurs, or frogs and velociraptors.

Perhaps the people trying to clone the Thylacine know a way around this. Perhaps they don't know what they're trying to do is impossible. Perhaps Misters Cohen and Stewart are the ones that are wrong. I'm certainly not qualified to say.

No comments: