Tag Archives: Cambrian

Clovis and after

The Clovis culture lasts less than half a millennium. But it coincides with a major change in the North and South American fauna: specifically with a wave of extinctions of large animals. We’ve seen something like this before with the human settlement of Australia. There’s still controversy about the causes, but it seems likely that humans played a major role in both extinctions, even if climate change also mattered.

The mass extinctions caused by humans differ significantly from the five generally recognized earlier mass extinctions, which mostly seem to have resulted from physical disasters, like asteroid strikes and poisonous gases. A better analogy for human mass extinctions might be found all the way back at the beginning of the Cambrian period, 540 million years ago. Then, a relatively low-key, more-or-less predator-free fauna (the Ediacaran fauna) faced a devastating challenge from newly evolved, mobile, visually guided predators. The Human Revolution may come to rival the Cambrian Revolution in its biotic consequences.

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The Burgess Shale and “Wonderful Life”

The Burgess Shale (about 510 Mya) is not the oldest Cambrian deposit known. There are deposits from China (Chengjiang) closer to the beginning of the era. But it is particularly rich and well studied. It also featured in debates about some Big Questions: How important are evolutionary laws versus historical accidents? Has the living world become more or less diverse over time?

Stephen Jay Gould (1941-2002) was one of the most widely known evolutionary biologists of his time. In 1989 he wrote a book about the Burgess Shale, called “Wonderful Life.” The title alluded to Frank Capra’s movie, “It’s a Wonderful Life,”* starring Jimmy Stewart. In the movie, the Stewart character, who thinks he’s wasted his life stuck in his home town, has a chance to see how things would have turned out if he had died young in an accident. He learns that his existence made a huge difference to his town.

Similarly, Gould argued that accidents of which Cambrian species survived and which went extinct made a huge difference to the later evolution of life. To make his case, he developed a subsidiary argument: that the Cambrian fauna displays a radical diversity of body plans in comparison with later eras. Gould made an analogy with the early development of automobiles, which featured diesel engines, steam engines, and electrical engines, before settling down on mostly just gasoline engines. (He was writing before Priuses and Teslas, of course.)

hallucigenia-wrong

Hallucigenia (wrong)

hallucigenia-right

Hallucigenia (right)

This subsidiary argument has not fared well. Most of the supposedly radically different forms from the Burgess Shale turn out to be not that radically different from one another, or from modern forms. Most notorious was the case of a specimen called Hallucigenia. Paleontologists thought that this creature was like nothing that ever lived before. But later more complete finds of related forms made it clear they were looking at it upside down; its “legs” are actually defensive spikes, the “tentacles” on top are actually legs. It’s probably related to the ancestor of velvet worms, a group related to vertebrates and still living in Australia. A different perspective comes from Simon Conway Morris one of the experts on the Burgess Shale, in in his book “Crucible of Creation.”

That aside however, the question of accident versus necessity, in evolution and in history, will continue to come up throughout the Logarithmic History year.

*Not to be confused with Jerome Bixby’s short story “It’s a Good Life,” about a very different small town.

Clovis and after

13.1 kya. The Clovis culture lasts less than half a millennium. But it coincides with a major change in the North and South American fauna: specifically with a wave of extinctions of large animals. We’ve seen something like this before with the human settlement of Australia. There’s still controversy about the causes, but it seems likely that humans played a major role in both extinctions, even if climate change also mattered.

The mass extinctions caused by humans differ significantly from the five generally recognized earlier mass extinctions, which mostly seem to have resulted from physical disasters, like asteroid strikes and poisonous gases. A better analogy for human mass extinctions might be found all the way back at the beginning of the Cambrian period, 540 million years ago. Then, a relatively low-key, more-or-less predator-free fauna (the Ediacaran fauna) faced a devastating challenge from newly evolved, mobile, visually guided predators. The Human Revolution may come to rival the Cambrian Revolution in its biotic consequences.

The Burgess Shale and “Wonderful Life”

The Burgess Shale (about 510 Mya) is not the oldest Cambrian deposit known. There are deposits from China (Chengjiang) closer to the beginning of the era. But it is particularly rich and well studied. It also featured in debates about some Big Questions: How important are evolutionary laws versus historical accidents? Has the living world become more or less diverse over time?

Stephen Jay Gould (1941-2002) was one of the most widely known evolutionary biologists of his time. In 1989 he wrote a book about the Burgess Shale, called “Wonderful Life.” The title alluded to Frank Capra’s movie, “It’s a Wonderful Life,”* starring Jimmy Stewart. In the movie, the Stewart character, who thinks he’s wasted his life stuck in his home town, has a chance to see how things would have turned out if he had died young in an accident. He learns that his existence made a huge difference to his town.

Similarly, Gould argued that accidents of which Cambrian species survived and which went extinct made a huge difference to the later evolution of life. To make his case, he developed a subsidiary argument: that the Cambrian fauna displays a radical diversity of body plans in comparison with later eras. Gould made an analogy with the early development of automobiles, which featured diesel engines, steam engines, and electrical engines, before settling down on just gasoline engines. (He was writing before there were Priuses and Teslas, of course.)

This subsidiary argument has not fared well. Most of the supposedly radically different forms from the Burgess Shale turn out to be not that radically different from one another, or from modern forms. Most notorious was the case of a specimen called Hallucigenia. Paleontologists thought that this creature was like nothing that ever lived before. It turned out they were looking at it upside down; its “legs” were actually defensive spikes. It’s probably related to the ancestor of velvet worms, a group related to vertebrates and still living in Australia. A rather different perspective comes from Simon Conway Morris one of the experts on the Burgess Shale, in in his book “Crucible of Creation.”

That aside however, the question of accident versus necessity, in evolution and in history, will continue to come up throughout the Logarithmic History year.

*Not to be confused with Jerome Bixby’s short story “It’s a Good Life,” about a very different small town.

The Origin of Seafood by Means of Natural Selection

The Cambrian explosion — shells and skeletons, and all the major phyla of today — is one of the major events in the history of life. It’s hard to miss – Darwin was well aware of it – because for the first time you have abundant well-preserved fossils of animals with hard parts. From now on, if I miss a tweet one day or another, it’s because I didn’t get to it, not because the evidence isn’t there.

Why the explosion happened when it did is unresolved. The early Snowball Earth episodes probably contributed in some way, and the rise of oxygen in the atmosphere must have been important. Maybe the explosion was less dramatic than we think: earlier forms are less well preserved, and may be hard to recognize as ancestors. Or maybe there was some dramatic biological event that triggered the explosion: the origin of eyes, and/or the beginning of predation, setting off an arms race between predators and prey that’s been going on ever since.

If this last possibility is correct, then the transition from an Edenic, predator-free Ediacaran world to the Cambrian is a form of “symmetry breaking.” There is an analogy here to the transition from an egalitarian society to a world of rulers and ruled in human social evolution.

Speaking of predation: the Logarithmic History blog is partly about commemorating great events in the past. It seems fitting to celebrate the Cambrian as the origin of seafood. If you took your time machine back to any time before the Cambrian, pickings would have been slim – algae mostly, although we don’t really know what the Ediacara would have tasted like. The time-traveller’s menu gets a lot better with the Cambrian (although wood for a fire is still a problem). Nowadays you can’t hope to dine on trilobite, alas. (Check in March 13 for more of this sad story.) But sometime in the next few days why not have some mussels for dinner? (The recipe below has some non-Cambrian ingredients. It will be a few more days, incidentally, before the evolution of anything kosher.)

Steamed mussels, 4 servings

Wash and debeard:
4 to 6 pounds mussels
Place them in a large pot and add:
½ cup dry white wine
½ cup minced fresh parsley or other herbs
2 tablespoons chopped garlic
Cover the pot, place it over high heat, and cook, shaking the pot occasionally, until most of the mussels are opened, about 10 minutes. Use a slotted spoon to remove mussels to a serving bowl, then strain the cooking liquid over them. Drizzle over the mussels:
1 tablespoon extra-virgin olive oil
Juice of 1 lemon
Serve with:
Plenty of crusty bread

Clovis, and after

13.1 kya. The Clovis culture lasts less than half a millennium. But it coincides with a major change in the North and South American fauna: specifically with a wave of extinctions of large animals. We’ve seen something like this before with the human settlement of Australia. There’s still controversy about the causes, but it seems likely that humans played a major role in both extinctions, even if climate change also mattered.

The mass extinctions caused by humans differ significantly from the five generally recognized earlier mass extinctions, which mostly seem to have resulted from physical disasters, like asteroid strikes and poisonous gases. A better analogy for human mass extinctions might be found all the way back at the beginning of the Cambrian period, 540 million years ago. Then, a relatively low-key, more-or-less predator-free fauna (the Ediacaran fauna) faced a devastating challenge from newly evolved, mobile, visually guided predators. The Human Revolution may come to rival the Cambrian Revolution in its biotic consequences.

Nature, red in tooth and claw

“You’re trying to live without enemies. That’s all you think about, not having enemies.” Isaac Babel, Red Cavalry

“Enemies are the most important agencies of selection.” Geerat Vermeij, Evolution and Escalation

Much of what we’ve been seeing since the onset of the Cambrian, Friday February 27, is the outcome of evolutionary arms races, leading to steady improvements in teeth, claws, armor, and mobility. It may well be that the onset of predation is what triggered the Cambrian explosion in the first place. The paleontologist Geerat Vermeij argues that arms races – not adaptation to the physical environment – are the greatest cause of progressive evolution. And we’ll see when we start getting into human evolution, biological and social, that enemies – other people especially – and arms races go on being a major motor of change.

Yet it’s sometimes among refugees from arms races that the greatest evolutionary advances arise: fish moving onto land may have been doing it partly to get to someplace where enemies were weak or scarce. Vermeij himself is competitively handicapped, having lost his sight at three years old, but has made a distinguished career studying shelled invertebrates by touch.