Rolston’s Understanding of “Possibility Space” in Evolution

Rolston’s Understanding of “Possibility Space” in Evolution

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The main difficulty I have with Holmes Rolston’s essay on “Possibility Space” is in his statement:

“We face questions about the increase of complexity and diversity, about contingency and inevitability in such increase, about novelty and progress.”

Looking over my notes from the April 19 presentation, I am struck by the comment that Rolston presents a fair amount of information about the increase in diversity — at least with respect to the number of taxa *preserved* for our examination. But showed nothing to support the assumption of increasing complexity. As the recent data from Ediacara and, of course the Burgess Shales, show, life was pretty interesting and diversity AND complex pretty far back. It is clear that vertebrates as we know them and flowering plants, for example, emerged late in earth’s history; but the kind of character state which Rolston seems to regard as “complexity” has more to do with specialization and coordination seen in vertebrate physiology, especilly us humans. But really, we are a pretty poor sample of the complexity of life out there and lots of what people used to call “lower” animals must be consider as complex and most of the “higher” ones, albeit it a different way.

The other issue is that of the anthropic principle. Vic Stenger has a “Toy Universe” program that he uses for teaching and research. The program allows the user to play with the “universal constants” and adjust the relationships between matter and energy and so on. After thousands of simulations, it is clear that there are *many* ways in which the universe could have been constructed and that many of these are quite suitable for the formation of life — although it would be life under a different physics than the one we know.

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I am also puzzled why calcium-and-phosphorus endoskeletons are more surprising than exoskeletons derived from chitin, diatomaceous silica, and calcium carbonate (which is left our here for some reason).

The vertebrate embryo, it seems, is an inverted invertebrate embryo — that is development proceeds in the opposite direction (upside down and backwards, as it were), so an internal-vs-external skeleton is not hard to explain. And we see an cartilagenous precursor of the skeleton in vertebrate embryos and young; calcification comes AFTER. The building block of the endoskeleton in vertebrates is cartilage — a few living connective tissue cells in a foundation of non-living protein and linked-sugar compounds (lovingly called “snot-and-slime” compounds by connective tissue specialists).

Rolston here is confusing the outcome with the process and misreading evolutionary biology badly. He seems to think that the vertebrate skeleton had to emerge in toto and in its present biological condition, but neither the fossil record, nor embryology and development, nor a minimal examination of the skeletal data across living taxa would support this starting assumption.

Indeed, this was my main objection throughout his presentation (and it goes back to the great american think-off contest); he seems to rely on sweeping interpretations and judgments levied by the “great thinkers” and not to be paying attention to the research from which these conclusions are drawn. Too often I found the basic biology to be quite disputable; and therefore the conclusions must be weakened.

Rolston writes:

“Biology, meanwhile, though prediction is often possible, is also full of unpredictable surprises–like calcium endoskeletons in vertebrates after millennia of diatomaceous silica and chitinous arthropod exoskeletons.”

Then there is this …

“…Nevertheless, there is the epic story–eukaryotes, trilobites, dinosaurs, primates–swarms of wild creatures in seas and on land, followed by humans who come late in the story.”

The problem is that these are only the survivors — even the extinct ones were experiments and modifications that succeeded enough to spin off a new taxon with sufficient number of members and sufficient duration that we were able to sample them in the fossil record. So, it seems like a progression; but it is more like the “drunkard’s walk” scenario that Gould uses. It only seems like a simple progression in retrospect when we look at the starting and ending points.

The point that evolutionary biologists make and which Rolston desperately needs to understand is that each event changes the probabilities (that is a matter of statistical theory), but also creates new possibilities which were not there in the previous step.

What is it in the common ancestor of humans and chimps that provided the possibility of self-recognition and of language use? We don’t know, but both taxa have it to some extent. Where are these traits in the common ancestor of these apes and other primates? Absent, as far as we can tell. Something occurred with the emergence of this lineage which would lead to the apes (including us) that set up different probabilities for these taxa than for others.

We can do this at any level — even on an ecosystem level. It’s pretty clear that the emergence of flowering plants and the rapid radiation of mammals are related. CHanges that produced flowering plants changed the ecosystems and opened up niches for small mammals (and for pollinating insects). So, the probabilities emerged out of the outcome of events and the interactions of systems to produce those events. In no way was it necessary for trilobites to have pollinating insects in mind, so to speak.

Andrew J Petto, PhD
Editor, National Center for Science Education 
Assistant Professor, University of the Arts, Philadelphia PA

Philosophy of Education: “Take Chances! Make Mistakes!! GET MESSY!!!” -Ms Frizzle