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POPPER AND THE PELVIS: AN ESSAY ON CONJECTURES AND REFUTATIONS

By January 27, 2017 No Comments

 

In the last issue of this magazine, it was pointed out by Todd Kliendienst (Organiser of the Karl Popper Philosophy Meetup Group, Brisbane), in a letter to the editor; that, while he enjoyed what I had written about Karl Popper, he felt obliged to point out that I was in error on a point of detail. I wrote, towards the end of the essay on Popper:

Popper did not venture into the arena of biology, but a similar story holds in that regard, of course. The bold conjecture by Charles Darwin that natural selection had driven a process of evolution and that the observable changes in the biological world were due to such selection pressures, opened up the biosphere and the human past to inquiry in a way that no creation myth had ever done.

The 20th century saw developments and refinements of this theory, with the integration of genetics into the picture and then the realization, only thirty years or so ago, that evolution had proceeded not through a gradual, progressive process, but via many changes and catastrophes of a quite haphazard nature – punctuated equilibrium. Little by little, our understanding had to be adjusted in the light of the refutation of assumptions or poor inferences embedded in the original conjecture.

All this was fine, Todd pointed out, except that Popper had ventured into the philosophy of biology.

This was freshly on my mind late last year when I got hold of the November/December issue of American Scientist, which features a story about new discoveries in palaeoanthropology that upend the conventional wisdom about the evolution of the human pelvis. What a happy coincidence, I thought, that on article in a serious magazine about conjectures and refutations in evolutionary biology – and human evolution, in particular – should appear in print even as I was being corrected on the matter of Popper and biology!

The article in question is titled ‘An Updated Prehistory of the Human Pelvis.’ It is by Caroline VanSickle, a specialist on anatomical sex differences in hominins base on the fossil record. It is a made to order case study not only in evolutionary biology, but in Popperian critical rationalism. The larger context for the piece, as she wrote is ‘The mystery of how humans came to be the only species of their kind on the planet.’ The problem, as she also points out, is that trying to figure this out is ‘a lot like working on a never-ending jigsaw puzzle without a box-lid for guidance and with most of the puzzle pieces missing.’ How could any intelligent person, at this point of her piece, not want to read on?

Here is her summary of what, in fact, passes for the box-lid – the up to date conjecture of specialists about the course of human evolution:

Sometime between 7 million and 13 million years ago, our lineage diverged form that of Pan troglodytes, the chimpanzee…At the end of the nineteenth century, when Charles Darwin was writing about human evolution, many scholars thought the evolutionary path to humans was a straight line. This conception seemed reasonable at a time when we hadn’t yet found many types of hominin fossils…Today, however, we have a lot more fossils to fit into the hominin lineage and what we’ve found is that evolution rarely proceeds in a straight line…This situation means that whenever fossil evidence of a new species is discovered, it has the potential to change the entire ‘map’ of human evolution. Lately, the map has begun to look less like a direct route than the roadways of a complex city, complete with dead ends, detours, roundabouts and side roads, representing both the fossils we know and the hominin species we haven’t discovered yet.

Having sketched this lid box out for us, she then cuts to the chase. Her own field is the evolution of the human pelvis. This, she hastens to advise the naïve reader, ‘is an important part of our evolutionary story, because the pelvis of hominins differs dramatically from that of the chimpanzee – and possibly, there, from that of our last common ancestor. ’

The conventional wisdom for some considerable time has been that the shape of the pelvis changed to accommodate the bipedal gait and upright posture that our ancestors adopted from well over three million years ago. The Laetoli footprints, from Tanzania, show that there were fully upright and bipedal hominins not less than 3.6 million years ago. The chimpanzee birth canal is elongated and spacious, allowing their small-brained infants an easy passage. The human birth canal is smaller and the infant’s brain larger, which results in the painful and difficult birth process for our species. It has long been assumed that as upright posture made birth more complex, the pelvis adapted to the emerging challenge. It just never quite adapted sufficiently to save human females the pangs of childbirth.

New evidence now suggests that this conjecture is false. Popper, I feel sure, would be fascinated. Up until about 15 years ago, VanSickle tells us, the available fossil evidence suggested that pelvic evolution had moved in only one direction, with the pelvis adapting imperfectly but steadily to accommodate bipedalism and upright posture. But in those past fifteen years, ‘a terrific sequence of fossil finds has provided enough additional evidence to change the picture.’ Here is the Popperian deductive process at work:

It now appears that paleoanthropologists need to find a different explanation for hominin pelvis variation than birth adaptations, because the old model does not fit the new evidence.

The most astounding such new evidence surfaced only in 2015, in the Rising Star Cave outside Johannesburg, where more than 1,500 human fossils were discovered; an extraordinary, even unprecedented abundance of matter.

As VanSickle remarks:

To find more than 1,500 fossils of the same species, representing nearly every part of the skeleton, including 41 pelvic fragments – often from multiple individuals of different ages – was like winning the paleoanthropological lottery. But there was a catch: What these new fossils told us about hominin evolution was confusing…Suddenly, it appears that mixing primitive and modern pelvic traits was relatively common in the past.

The scale of the find and its radical implications reminds me of the discovery of the Nag Hammadi Library in Egypt in the 1940s, with its trove of gnostic gospels and their implications, which threw open the field of New Testament scholarship. But the Rising Star Cave finds takes us back a whole lot further than anything in the Bible ever did! And its holdings confront us with a beautiful Popperian question. In VanSickle’s words: ‘If birth constraints do not explain the pelvic variation of the past, that must mean we don’t really understand why human pelvises look the way they do today. In the absence of any simple answer…paleoanthropologists have started to consider more complicated possibilities.’

There are now several hypotheses being considered, one of which is that human pelvis shape has been shaped by diet and that a carbohydrate heavy diet, after the invention of agriculture, has been the main cause of problems with the birth canal. This, at least, ought to be fairly readily testable. In any case, as VanSickle observes, testing this and other hypotheses ‘will call for developing a better understanding of what causes variation in the shape of the modern human pelvis’. She adds a salutary comment about the nature of inquiry:

It seems to me very likely that we scientists have spent so much time focused on figuring out how birth explains the evolution of the hominin pelvis (only to realize belatedly that it might not), that the real explanation may be something we haven’t thought of yet.

So it goes when inquiry is open and scientific. This plays directly into Popper’s argument for critical rationalism and freedom of discussion. We need to revitalize that argument right now, because there are far too many parties abroad in the world whose approach to matters of knowledge is dogmatic, sectarian, partisan and anti-liberal.

As Popper wrote in 1963, in Conjectures and Refutations (p. 352):

Truth is not manifest; and it is not easy to come by. The search for truth demands at least

  1. Imagination
  2. Trial and error
  3. The gradual discovery of our prejudices by way of a and b and of critical discussion

The Western rationalist tradition, which derives from the Greeks, is the tradition of critical discussion – of examining and testing propositions or theories by attempting to refute them. This critical rational method must not be mistaken for a method of proof, that is to say for a method of finally establishing truth; nor is it a method which always secures agreements. Its value lies, rather, in the fact that participants in a discussion will, to some extent, change their minds, and part as wiser men.

It is striking that he wrote ‘men’, in 1963; but we can be confident that this was a linguistic convention, not a prejudice on his part. We might add, moreover, that it was too sweeping to say that critical rationalism derived from ‘the Greeks’, as if it had been a racial or cultural trait. It was not. It was the brainchild of a small subset of Greek thinkers, who (like Anaxagoras and Socrates) were at times persecuted for their critical rationalism.

Such thinking is a human possibility. Variations in its occurrence and practice, like variations in the shape of the pelvis across evolutionary time, call for careful analysis and explanation, not glib assumptions. The statement that the ‘Western’ rationalist tradition has the quality of considering and testing hypotheses is less narrowly racial than the claim that ‘the Greeks’ hold pride of place, but it has the same limitation. The great majority of people in the Western world have never been any more scientific or devoted to critical rationalism than human beings elsewhere. Those things have always been the work of a sub-culture and they require constant nourishment, institutional embodiment and active exercise in order to survive. That is as true now as ever and if we are to bring a viable new global economic and ecological order to birth in the 21st century, we will need to work hard at getting the cultural birth canal into shape. Let’s go to it.