Notes on ACAAPNZ 2008 II

A third selection from the 2008 annual conference of the NZ division of the Australasian Association of Philosophy

Tool Use and Life History of Early Homos. Ben Jeffares (ANU).

How to account for human cognitive and social evolution? One approach is to focus on the physical evidence of human evolution (skeletons, tools, drawings, etc.) and on the periods where this physical evidence indicates dramatic changes in human life, thought and behavior. This is Jeffares' approach, and in this talk he concentrated on a dramatic change in human tool use that seems to have taken place around 1.5 million years ago.

1.5mya is a hotspot for archaeologists because it's meant to be the great coming of age of our species – the point where we stopped being walking chimps and became hairy humans. And a jump in tool use is the main marker of this shift. Jeffares thinks tools were around well before the point where the first appear in the archaological record. Skeletal remains indicate that early bipeds had a hand structure suitable for tool-use well before 2.5mya. Be that as it may, tools became more refined around 1.5mya, being more symmetrical and sophisticated and more likely to be “time travellers”: made in advance and for repeated use.

How to account for this change? It's really quite interesting, but the evidence is fragmentary. Studies have suggested that homos started living differently around the time that tool-makers sharpened their act. The started having longer childhoods, longer periods of learning and maturing: the age of the teenager had begun. They also had patchier resources, had to kill away from home and in unknown places. So they had to plan ahead, making tools at home using secure resources. And, crucially, the children sat around while the tool-makers worked, and the tools lay around as well. Teaching ensured that any new skills or gizmos could be passed on. And the tools that lay around acted as “templates”, finished products that young killers could copy. As Jeffares put it, students could learn from “products”, not just from “behaviors.”

A nice story, but is it true? Jeffares is sensitive to the weaknesses of the evidence, and with good reason. It is not an exaggeraion to say that the extended-childhood data is based often based on “half a dozen teeth.” Human evolution is light on evidence and heavy on theorising – not necessarily a bad thing, and good for philosophers. There's some doubt about Jeffares' early tool-use thesis. Tools are not the only reason that manual dexteritry, of the kind found in skeletal remains, can arise. As Sterelny puts it, “it's always important to be able to scratch your bum.” Turning over rocks for food, extracting berries or flesh, forcing other animals to the ground: all would need precise and powerful grips.

Some will also question the inference from stone-crafting to tool-use. Some of the stones in question are beautifully symmetric, crafted beyond the needs of mere huntsmen. They have the look of ornaments, icons. Jeffares insists, though, that the elegant tear-drop stones are the exception. And there's no need to worry about the fact they have a sharp edge all the way round. True, this would make them inpracticable as hammers or weapons. But they were not always like that, says Jeffares. Whenever one edge wore out, our frugal ancestors worked on another edge of the same stone -- and so on until the stone was crafted all the way around. It's only the finished product we see.

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Notes on ACAAPNZ 2008 II

A second highly selective selection from the 2008 conference of the NZ branch of the Australasian Association of Philosophy.

When not to have an Argument: the Different Explanatory Goals of Population Biology and Evo-Devo. Brett Calcott (ANU)

This talk was an attempt to resolve (in so far as it can be resolved) the debate between population biologists and evolutionary developmental biologists. A persuasive talk, but Calcott may have missed something important. I should note that part of Calcott's project is to unify evo-devo explanations with pop-bio explanations by showing how they both fit into a single account of explanation -- the “difference-maker” account of explanation. But the meat of the talk comes in Calcott's account of how explanations differ between the two approaches to biology.

Calcott distinguishes between “population-level” and “individual-level” explanations for evolutionary change. The former uses the genetic make-up of a population, plus the mathematical theory of genetic change, to explain changes in that genetic make-up. The latter uses certain physical differences between two stages in an individual's evolution, plus a knowledge of bioengineering, to explain certain other physical differences between the same two stages.

Calcott elaborates this distinction by saying that the former explanation is one of motive, and the other of means. Imagine an explanation of why a child got the chocolate bars on the top shelf in the kitchen. One could say that the child liked chocolate very much, so he was motivated to get it. Or one could say that he used a stool to help him reach the chocolate – he had the means. Both of these are genuine explanations of the child's behavior; whether we are satisfied with one or the other will depend on what we already know and what we want to find out. We can't ascribe motives to evolution, of course. But it seems reasonable to distinguish between what drives an evolutionary change (gene frequencies and their interactions) and what facilitates it (ie. how adaptive changes in structure to an individual are underwritten by other structural changes).

If this distinction holds, two things are clear. First, Calcott's distinction cuts across another popular distinction that is sometimes used to account for the disagreements between evo-devo and pop-bio – that between “proximate” and “distal” explanations. How can we explain, say, the human scab? We could give a biochemical account of why blood goes hard when exposed to air, and how this helps to heal the wound underneath. We need not look to the past to do this. Or we could try to explain how the tendency to form a scab has evolved – how it has come about that humans have the kind of biochemistry that leads to scabbing. This would certainly involves studying the past. Sometimes evo-devo is said to give “proximate” and pop-bio to give “ultimate” explanations.

Against this, Calcott insists that individual-level explanations, as he describes them, can account for how current phenotypical traits came about. After all, those explanations tell us how the structure of an individual at one point of time leads to a different structure in the same individual at another time. It tells us the mechanical means for this change. If we want a more fine-grained account of change over time, we just give a continuous series of these individual-level explanations.

As Calcott points out, certain “lineage diagrams” do just this. The lineage diagram we all know is of human evolution: a series of imags of our species in profile, running from the hunched and hairy ancestors to the pale and upright modern human. This doesn't explain much. But a more sophisticated diagram might. To illustrate, consider a set of instructions on how to make an oragami figure. These usually consist in a series of five or six drawings of different stages along the way to the final figure. And each drawing has dotted lines and arrows that tell you how to get to the next figure – what combination of small changes are needed in order to add a wing here, an envelope there, a sharp point there. Producing these “instruction series” is one job of biologists, and Calcott has all the right slides to show that they take the job seriously.

Calcott is clear that his distinction between individual-level and population-level explanations defuses the debate between evo-devo and pob-bio, rather than resolving it. He points out that the two forms of explanation he describes can come into conflict. That is, one form can give an explanation of a phenomenon that the other can refute. In any particular case of such a conflict, there can be a dispute about which account should hold more weight. But this is just as reconcilable as any other dispute in science between two competing explanations for a phenomenon. No two correct explanations of the two kinds could ever disagree over the facts of evolution. In this sense, they are “commensurable.” What should not be disputed is that both of them can give insight into how species have evolved.

Now, all of this strikes me as pretty well on the right track. But I'm not convinced that Calcott has covered all the areas of serious disagreement between evo-devos and pop-bios. As I understand them, evo-devos do in fact propose a new population-level process of evolution. The don't just give us, for each evolutionary event, an account of how certain structural changes are grounded in other structural changes. They give us an alternative view of how natural selection occurs. On the old view, genotypes fix phenotypes. And evolution occurs when a new and better genotype is randomly produced and outlasts the other ones. On the new view, genotypes have a very loose hold on phenotypes. Evolution occurs when the environment changes and phenotypes change in response to it, without any genotypical adjustments occuring. Genes only change further down the line. They help to ground the new phenotype, but the new phenotype arose earlier and independently, as an adaptive response to the environment. In a phrase, phenotypes lead genotypes, and not the other way around.

One can argue about whether this new picture is really new, or just a new angle on the old one. But it is a matter of sociological fact (I thought, perhaps wrongly), that the evo-devo picture was, and is, new enough in appearance to cause a big split between the evo-devos and the pop-bios. And this really does seem to be a split about the way in which evolution occurs, not about two different patterns of explanation that can be applied to evolution. Hence Calcott's distinction does not help to heal this particlar split, even if it can heal others.

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Notes on ACAAPNZ 2008

ACAAPNZ = annual conference of the New Zealand branch of the Australasian Association of Philosophy

Naturally, the Australasian Association of Philosophy has a New Zealand branch and (just as naturally) this branch has a regular conference that takes place in New Zealand. Oddly, though, the 2008 conference had a lot of Australians. But there's a natural explanation for this. The Australian National University can't find enough top Australian philosophers to fill their gaduate programs, and New Zealanders get first pick of the international scholarships at the ANU. Couple this with the fact that some top thinkers at ANU have dual careers in the big and small islands of the South Pacific, and you get quite a lot of inter-breeding. And when the man with the dual careers is Kim Sterelny, the scruffy luminary of cognitive evolution, you get quite a lot of Australian philosophers of biology at your New Zealand conference. This is all to the good, of course. But it means there's lots of philosophy of biology in the following notes on the conference, and not a whole lot else. So in here (in this and the following two posts) is my very selective list of conference talks, and some thoughts on them.


Presidential Address: On Turing on Intelligence as an Emotional Concept. Diane Proudfoot

A curious talk with drama, video, and a spiky question-time. The puzzle about the Turing Test is that Alan Turing's original version of the test seems needlessly complex. It consists in a jurer who asks questions of two hidden objects. One is a real person and the other is either a real person or a computer imitating a person. The jurer's task is to judge whether the second object is a real person or not. But it seems like one could just as well get rid of the first hidden object, and ask the jurer to judge whether it is a human or not.

Proudfoot thinks that the more complex test was better for Turing because he thought of mind as an “emotional” and not just an “intellectual” concept. Which is to say that whether we judge an object to be thinking or not depends on “our own state of mind and training”, which can vary between judges.

Proudfoot drew on three bodies of data, two sociological and one historical, to make her case. One is that humans are naturally credulous when interacting with computers. This can be nicely demonstrated by quirky videos of humans led into conversation with blocks of moving metal. Another is that humans guard their uniqueness jealously. We don't like being taken in by mere metal. At the annual Turing test Olympics, humans are more often mistaken for computers than the other way round. The historical fact is that Turing did indeed say that thinking is “emotional” in the way described above.

What to say about these bodies of data? The audience consensus seemed to be that they are interesting, but that it is not clear how they explain Turing's preference for the more complex test. Perhaps the idea is that the complex test brings out our jealousy to counteract our credulity. But how does the complex test accomplish this? And if mind really is an “emotional” concept, then the judgements we naturally make about the intelligence of machines should be our raw data about that intelligence, not fallible hunches.

To the second question, Proudfoot responds that according to Turing, our emotional response to a machine is only one component of the machine's intelligence, the other component being a fact about the machine itself. So Proudfoot would presumably claim that our credulity is not part of the subjective component, and is fallible. She did not give grounds for this claim -- even so, it can still form part of a how-possibly explanation for Turing's complex test.

The drama from the talk came from a mock-up of Alan Turing's 1952 broadcast on the BBC. Not all the original listeners liked the original broadcast. One listener said it sounded as if it had been “read from a prepared script, and badly.” Others were flatly opposed to the idea that machines could think. The mock-up got a receptive audience, though, not least because it shown the hidden dramatic talents of some professors of logic – talents great enough that noone could work out who they were.

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Cancer and stem cells: what's the connection?

Economist article leaves something to be desired

This week's Economist (Sept 13-18) put on a show about cancer research and stem cells. The front-page byline is: "The connection that could lead to a cure." Great for pulling in readers, but did the article live up to the cover? Yes, because it's explanation of the science made sense, it was duly cautious about "cures", and it had a bit of history.* From the article, however, it is not easy to know what the fuss is about.

Stem cells and cancer research are certainly converging. Scientists are getting keen and holding meetings on the topic, and drug companies have tentatively mined the field. Researchers have got some promising results, though no decisive ones. One class of study involves separating out two different kinds of tumor cells and measuring their effects on animals -- mice seem to be the in thing here. One kind of cell is no more harmful than a needle prick. The other kind leaves the rodents with a fat brown cancer. Experiments like this were done in 1997 on leukemia, in 2003 for breast cancer, and since then for a long hit-list of different cancers. The bad news is that some cancer victims have died within 14 months even when their tumors housed no stem cells (at least as far as scientists could see, which is not very far in these cases).

But 1997 is a long time (and lots of mice) ago. According to the article, scientists have taken two main strides since then. One is a the use of targeted drugs to weaken stem cells against radiation treatment. The other is the discovery that the non-stem-cells in tumors can morph into stem-cells. As the Economist author points out, this is a blow to the view that stem cells are at the root of the problem.

All this is exciting and equivocal, and the author conveys both aspects. But I don't see what stem cell research has to do with it. I want to know: of all the detailed research that has been done about stem cells, which bits of it help us to understand the behavior of stem cells in tumors, and ultimately to get rid of them? What have scientists learnt from growing livers that can be used to dissolve cancers?

Granted, it's useful to know that cancer cells are of two kinds, and that they breed in the way that stem cells do. But does it tell us something about their chemical structure that we didn't know already, or about their susceptibility to particular drugs, or their life cycles or self-dispersing behavior? I couldn't find much of that kind described in the article.

It's true that one strong lead, noted in the article, is to use a drug developed by the biologist Craig Jordan (Rochester, NY State), and which is known to kill normal stem cells. But the article reads as if this drug was developed to target cancer cells, not stem cells -- it's not clear how the knowledge that the cancer cells are stem cells contributed to the discovery. (I would also quite like to know *when* Craig Jordan made this discovery, which you won't find out from reading the piece).

Recall the byline on the Economist cover. I see the cancer research and stem cell research in the article, but I don't see the connection.


* But one thing puzzled me about the history. The story goes that before the stem-cell theory of cancer there was the mutation theory -- that's where normally sterile cells mutate and start making babies, but they don't have much practice and they make really bad babies. According to this theory, in a healthy body only the sex cells reproduce. But how did people explain the healing of wounds, the growth of hair, and all of the other cell-consuming human events, before the stem-cell theory arrived? Was it just that there was a big lag between the idea of stem cells and their application to cancer?

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