lpetrich

However, there is an alternate scenario that goes like this:

Some extraterrestrial visitors arrive at the Earth about 580 million years ago and set up a big floating genetic-engineering lab. The Earth had just come out of a sequence of big ice ages, and the visitors were curious to see how much had survived. And they found that various algae and fungi and protists and bacteria had survived in the Earth's oceans and rivers and lakes, with some of them inhabiting the soil.

But they were dissatisfied, and they wanted to see more. So they took some flagellate protists and started exploring the microbes' genes and internal mechanisms. When they were satisfied that they had learned enough, they decided to see what they could create from these protists.

So over the next several million years, they did lots and lots and lots of genetic engineering, producing the beginnings of all the animal phyla.

Kosh

NOTICE: You have just violated the non-disclosure
agreement you signed with the Vorlon empire.
Our starships are are enroute to annihilate your
planet, unless you can tell us the answer to
the ultimate question.

Buckster

Ah! Finally!! My chance to save the world!!

42!!

I hate Vogon poetry...

Oolon Colluphid

Actually I quite like it. Some of the metaphysical imagery counterpoints the surrealism of the underlying metaphor of the, er, Vogonity of the poet’s compassionate soul.

Buckster

Hmmm... You may have a point.

Perhaps I should try it without a babblefish in my ear... Hold my towel a moment...

lpetrich

Cute comment as to who revealed the secret. I'll now imagine some vignettes of extraterrestrial genetic engineers in action in the Vendian and early Cambrian.

I imagine those genetic engineers to be software personalities inhabiting the control computers for their machines, which form a vast network. I'll give them the names of some well-known evolutionary biologists for convenience.

Tom: Whew! Our new home has passed the tests. We are now ready for action. We're now off the western shore of Laurentia, at the Burgess Banks continental shelf. Ernie has been sent to the nearby land.

Ernie: I've gone several km inland. And so far, no macroscopic life has been identified. However, the soil is a greenish color, and I looked more closely at it and found algae growing in it.

Charles: I've found some algae-eating protists in those river-mouth-algae-mud samples Ernie had sent me, and I've succeeded in producing a self-sustaining colony in a tank.

Some time later, Ernie has scoured most of the land area of the Earth and found it to be devoid of serious multicellular life, and Lynn has likewise done that for the oceans.

However, Charles has been tinkering with the genes of his protists, and he's succeeded in making them form colonies. Tom wasn't impressed -- lots of organisms form colonies. But Charles wanted them to take definite shapes, shapes that would be useful to them.

He succeeded in making a big mass of these protists that had lots of holes in it for them to circulate water and released them into the environment.

They multiplied, but the others weren't impressed -- a big amorphous mass wasn't exactly something to be proud of.

So Charles went back and tried a more advanced design. He decided to take the tube-forming expertise and make a fancier tube with tentacles in front that would shove food in. This was a tough design project, and Charles had to make the cells specialized, with some of them being specialized for changing shape and some for rapid communication. And Charles had to work out how to wire the communication cells properly.

Tom wondered why Charles was exclusively working with the diploid phases and letting the haploid phases stay single-celled; Charles said that it's convenient to have the haploid phases single-celled, because haploids from different diploids can meet and join and make a new diploid.

Several million years passed, mostly of observing and snoozing, when Charles got a newer idea. He decided to create a really fancy worm. For convenience, it was segmented, its neural tissue was concentrated in a strip the length of its belly, and its digestive system extended the length of its body.

Tom noted that these worms had a hard time growing very big -- it became hard for food to diffuse throughout its length. So he created an ectopic throat above its real throat whose swallowing motions circulated the worm's internal fluid. Charles thought that that was weird, but it worked.

The worms were released, and they proliferated in the algae-matted ocean floor. Lynn and Ernie were soon reporting the worms elsewhere in the world, alongside their earlier creations.

So they started working out variations on the worm theme. Tom created a version that liked to lie on its back, collecting food from above -- eventually, that worm grew a new mouth and effectively became upside-down.

Charles, however, thought about how to make the worms stiff, and he thought of an idea: make its skin stiff. But the worms would have to crawl out of their skins as they grew -- which he also implemented. Tom thought that that was an odd thing to do, but it worked.

Charles also had the idea of making the segmentation work in the limbs of some of these creatures, and he came up with worms with jointed limbs.

And soon, all these modified worms were crawling all over the seafloor, eating up all the algae there; floating algae was more difficult to catch, and some of the worms took to swimming.

Eventually, Charles and Tom and Ernie and Lynn and the rest decided that they'd prefer to watch than to create -- their work had become the foundation of the evolution of a great diversity of life.

[ February 23, 2002: Message edited by: lpetrich ]</p>

mac_philo

The Cambrian Explosion was a period 600 million years ago when multicellular organisms really god a head of steam going. In the early 20th century Charles Walcott found and classified a set of Cambrain fossils at Burgess Shale, British Columbia. By any standard these fossils were remarkably well preserved.

In the 1970's these fossils were reclassified. This brilliant reclassification showed many phyla otherwise unrepresented. In other words we were shocked by a lot of new phyla.

The tiff is over the importance of this. For Gould, it says something important about punctuated equilibrium, the improbability of life evolving, the periodic nature of evolution, etc... Somehow this is supposed to challenge the view that natural selection can account for all that there is. For people like Dennett, the Cambrian explosion and the 1970's reclassification are interesting topics that we should analyze, though they see no implications for the theory of evolution.