http://www.msnbc.com/news/754908.asp

-- Stephen M. Poole (smpoole7@bellsouth.net), May 20, 2002

Answers

A great writer and a respected scientist. He was one of the authors of the Theory of Punctuated Equilibrium - a recent (and widely accepted) refinement of Darwin's basic theory. Too bad. He was only 60. Now I can't look forward to reading his next few books.

-- Little Nipper (canis@minor.net), May 20, 2002.

LN--

Can you elaborate on Goulds's notion of punctuated evolution? I have never read Gould. Punctuated evolution connects for me in the sense that it is fairly obvious that evolution is not gradual. Each generation is not a millimeter more evolved than the previous generation. Modern homo sapiens is the same creature that created cave paintings in France 20,000 years ago but it is a different creature than the one that wandered the African savannah a million years ago. So at various times there must have been "step" changes (a little engineering lingo there) in our evolution. How does Gould explain this?

-- (lars@indy.net), May 20, 2002.

Lars,

Good article from Scientific American

-- Stephen (smpoole7@bellsouth.net), May 21, 2002.

With the understanding that I am merely stating my layman's viewpoint and am likely to oversimplify, here's how I would sum up Gould's theory.

Within a given ecosystem the mass of lifeforms that make up the ecosystem, from plants to bacteria to predators, reach a certain equilibrium. Each species has adapted to the way things are.

Under these conditions, genetic variations continue to occur, but the only variations that are selected are those that are massed near the center of the bell curve of what's "normal" for that species. Variations at the outer edges of the curve don't conform well to the prevailing conditions. The species remains stable and does not evolve. That's what we observe most of the time.

From time to time, the prevailing conditions change. Not just a temporary shift, such as a drought, but a fundamental shift, such as an ocean current relocating. Life forms that had adapted to a niche that changed may find the rug pulled out from under them. The mass of their genetic variation will still cluster near the center of the bell curve, but to quote Yeats "things fall apart, the center cannot hold". Under such circumstances, some variations near the edge of the curve may become more adaptive to the new conditions.

When this happens, the mass of the species will suffer, struggle, become ill-adapted, lose population and become marginalized, but the lucky individuals who inherit unusual, but marginally more adaptive traits will form a very small cohort within the species. This cohort will rapidly move away from the "norm" and within a geologically short time form the basis of a new species.

That is my best understanding of what Gould thought happens.

-- Little Nipper (canis@minor.net), May 21, 2002.

Thanks. That makes sense. I think it says that a step-change in evolution is driven by a step-change in environment. So we are unlikely to see more evolution until the mag poles reverse, an ice-age begins, etc.

One problem I see here is that this view doesn't necessarily predict that evolution will always lead to a more advanced creature, does it? Nor does it explain how cro-magnon man and neanderthal man coexisted (ie, we did not evolve out of neanderthal, which doesn't mean there wasn't some hanky panky between the two)

All I know is that we are here, wherever "here" is.

-- (lars@indy.net), May 21, 2002.

You really ought to pick up one of Gould's books of essays, Lars, just to see if it appeals to you. His writings are exemplary, in that they are clear, lively and interesting without the usual problems of "popularizing" science books-- he doesn't dumb it down or get the details wrong. He wasn't just a great scientist, but also a great teacher.

Anyway, to address a couple of your comments. Human activity is making fundamental and profound changes to ecosystems all over the world right now. Just the population loss among predator species in the last century alone has been of cataclysmic proportions -- not to mention the loss of habitats of all kinds. I doubt we are a temporary condition, either. We still may not "see" the evolution we are provoking for another 10,000 years, but that is an eyeblink in evolutionary time.

As for the "problem" that evolution doesn't necessarily produce more "advanced" species - that isn't a problem at all. It doesn't. It only produces species that live and reproduce. That is the only measure of success that species "strive" for.

Complexity is not an end in itself, but only one possible means to an end. Bacteria are still the most successful organisms on the planet and always will be -- with algae in second place. We happened to evolve intelligence and opposeable thumbs because the intermediate steps between our ancestors and ourselves were each successful in their own way and for a time, and the aggregate effect was to produce the species we have become.

Gould has some wonderful essays on this misconception. I don't recall the titles or which of his many books they appeared in. What is far more important than those is what I do remember -- the beauty and clarity with which he explained this concept and the welcome feeling of understanding what he was saying.

Try his book Wonderful Life and see if you get hooked.

-- Little Nipper (canis@minor.net), May 21, 2002.

LN:

Of course that explanation doesn't agree with the view that the vast majority of surviving mutations are neutral [as they relate to survival; which is what you are talking about; when they don't, they are lethal; most mutations are]. Using your explanation, most of the mutations would remain in the middle of the bell curve [where, indeed, most of the population resides]. Social or environmental changes would then select from the middle of the curve and not from the edges.

Best Wishes,,,

Z

-- Z1X4Y7 (Z1X4Y7@aol.com), May 21, 2002.

Z, interesting point. But why should survival-neutral genetic traits be present in more than a small cohort, since there has never been any selective pressure to spread them?

-- Little Nipper (canis@minor.net), May 21, 2002.

Little Nipper,

Not sure if this answers your question but here is a quickly found quote from John Maynard Smith's book Evolutionary Genetics where he is assigning a computer project to the reader.

"Simulate genetic drift. Start with a population of N asexual types, all different. produce a new population by random sampling, and continue until all are identical. Use the program to check the statement that the expected time is 2N generations, with a standard deviation a little greater than N."

-- dandelion (golden@pleurisy.plant), May 21, 2002.

Wonderful Life? Didn't they make a cornball movie from that?

-- (lars@indy.net), May 21, 2002.

Yep Dandy:

LN:

They are, of course, random; hence they are more common in the largest population segment. That would be in the middle of your curve.

Of course, this could all be wrong; it is just the current thinking. I am not working in the area, but I have 15 or so seminars to choose from each week; sometimes I go to the ones on evolution. The ones on mutational clocks can drive you nuts. Man, when they give you one slide comparint 50 sequence analyses, you become cross-eyed ;<)

Best Wishes,,,,,

Z

-- Z1X4Y7 (Z1X4Y7@aol.com), May 22, 2002.

LN:

But why should survival-neutral genetic traits be present in more than a small cohort, since there has never been any selective pressure to spread them?

As I understand the argument, they are present in a small cohort; but a large number of small cohorts. Since they generally serve no purpose, they aren't selected against. When some social or environmental change makes them survival positive; that cohort survives. At least that is the present thinking. Of course, time may change that thinking. This isn't religion. ;<))

Best Wishes,,,,,

Z

-- Z1X4Y7 (Z1X4Y7@aol.com), May 22, 2002.

Of course, time may change that thinking. This isn't religion. ;<))

You bet! We change the "truth" daily to accomodate the nuances of quantitative methods.

-- (Dr Strangelove @ my Skinner.box), May 22, 2002.

Of course my good Dr. "truth" is only availble to religous fanatics. Everything else is called intelligence. Gawd, I am now sounding like Flint.

LN:

The system that I study involves two organisms. It is reported to be the most recent mutualistic associations; circa, the end of the last ice age. I go to these things because it helps me to think about the association and how to understand it. For you libertarians out their; this association caused nearly 1 billion dollars of loss to the economy last year [government estimates]. For you envirnomentalists out there; it is causing a massive ecological change east of the Mississippi. It will move west. ;<)

Best Wishes,,,,,

Z

-- Z1X4Y7 (Z1X4Y7@aol.com), May 22, 2002.

There is no "truth". All "truth" is a social construct. Indeed, Deconstructionism itself is a social construct. So there!

-- (Jacques Derrida@postmodern.deconsructionism), May 22, 2002.

Croaked but not forgotten. Let us hope he contributed to the gene pool. We know he contributed to the "collective unconscious".

-- (Il Papa@Vat.City), May 24, 2002.