Tuesday, 28 July 2015

Pygmy Puzzle for Creationists

Baka Pygmies of Gabon
Growth pattern from birth to adulthood in African pygmies of known age : Nature Communications : Nature Publishing Group

How do African Pygmies make the 'Intelligent (sic) Designer' look like an incompetent amnesiac?

Imagine you're a designer and you design something that's fit for purpose and does the job perfectly, why would you start again and design something else to do exactly the same job? Well, maybe if you're a chronic amnesiac and can't remember from one day to the next what you've designed, you'd maybe have an excuse, but you're hardly likely to be much of a designer and certainly not what people would regard as an intelligent one.

The problem is, if you want to believe in an intelligent designer as the best explanation for just about everything you don't understand in biology, cosmology, physics, geology, etc., this is what you are required to believe constitutes intelligent design - starting afresh every time and coming up with lots of different ways to do exactly the same thing, even when starting from the same point - a bit like a designer who keeps designing wheels.

As I described almost a year ago here, researchers discovered that two different groups of Pygmies have genomes that don't overlap, showing that their short stature evolved separately and independently in a case of convergent evolution. Now, another team of researchers have shown that short stature results from two entirely different growth processes.

Abstract
The African pygmy phenotype stems from genetic foundations and is considered to be the product of a disturbance in the growth hormone–insulin-like growth factor (GH–IGF) axis. However, when and how the pygmy phenotype is acquired during growth remains unknown. Here we describe growth patterns in Baka pygmies based on two longitudinal studies of individuals of known age, from the time of birth to the age of 25 years. Body size at birth among the Baka is within standard limits, but their growth rate slows significantly during the first two years of life. It then more or less follows the standard pattern, with a growth spurt at adolescence. Their life history variables do not allow the Baka to be distinguished from other populations. Therefore, the pygmy phenotype in the Baka is the result of a change in growth that occurs during infancy, which differentiates them from East African pygmies revealing convergent evolution.*


In this open access paper, the authors provide the following background information:

African pygmies live in equatorial rain forests and grow to an average adult stature of <155 cm. They share an economy based on hunting and gathering and a complex socioeconomic relationship with their farming neighbours. Moreover, in each case pygmy peoples are identified by their culture and behaviour as pygmies by farming neighbours, who in turn identify themselves as non-pygmies and are recognized as non-pygmies by pygmies, as well as by other non-pygmies. Pygmy populations are distributed across equatorial Africa in two main clusters. One is in East Africa (Ruanda, Uganda and Eastern DRC) and comprises (following Schebesta, Gusinde and many others nomenclature) the Aka, Sua, Efe groups (also frequently called ‘Mbuti’) and the Batwa. The other cluster, in West Africa (Cameroon, Central Africa Republic, Congo, Gabon and Western DRC), includes the Kola, Bongo, Koya, Aka, Baka and Twa. Pygmies share a common ancestor and splitted from Bantu-speaking populations at around 60,000 years BP; the split into an eastern and a western cluster would have taken place later than 20,000 years BP. Substantial admixtures between pygmies and non-pygmies have occurred in the last ~1,000 years. Even today, the main barriers to admixture are the cultural and behavioural differences between these two groups. The pygmy phenotype itself is usually interpreted as an adaptation to life in equatorial rain forests. Studies of genetic introgression have shown that the pygmy phenotype stems from genetic foundations, perhaps involving a deficiency in the GH–IGF axis. Although some particular SNPs in genes associated with stature have been identified in pygmies the exact genetic foundation remains elusive.* [My emphasis]

By measuring their growth from birth over a 25 year period (i.e., into adulthood), the team from CNRC, IRD and UPMC have shown that the two groups take different growth paths to pygmy stature. The Baka are within the normal range for humans at birth but their growth rate slows significantly until the age of about three. From then on they grow according to normal growth patterns. The other group, on the other hand, are born small and simply grow more slowly.

So, the same adult phenotype is achieved in entirely different ways, neither of which appear to be better than the other and both of which seem to be equally good at achieving the same thing.

And they have evolved during the last 20,000 years since the two groups diverged and both groups have evolved in the last 60,000 years since diverging from the Bantu.

Would any creationist like to offer an explanation for this situation, where it looks like their assumed designer was neither intelligent nor aware of what it had already done? In what way is an evidence-free notion which not only involves magic but for which excuses need to be made for the ineptitude of the magician, better than an fully understood natural process that doesn't involve magic or an inept magician?

The environment favouring certain variations, with no concern for the genetic basis for that variation, and acting independently on two isolated groups, is, of course, a perfectly good way of explaining this difference without invoking magic or having to make excuses for a magic designer's ineptitude.

Quite simply, the two groups weren't designed; they evolved independently.

Cue: denialism, avoidance, redefinition of 'evolution' and probably abuse.

*Copyright © 2015, Rights Managed by Nature Publishing Group, reproduced under terms of Creative Commons CC-BY licence.

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