Wednesday, April 22, 2020

British hipsters

Why have British women become broader-hipped over the past three thousand years? (Wikicommons: Niek Sprakel)

British women have become broader-hipped over the past three thousand years or so. That's the conclusion of a recent study of alleles that influence female hip circumference, using data from the UKBiobank. 

Audrey Arner and her colleagues at Penn State identified 148 SNPs associated with female hip circumference and 49 SNPs associated with first child birth weight. Nine of them influence both women's hip circumference and first child birth weight. The SNPs associated with female hip circumference seemed to influence first child birth weight but not vice versa. There also seems to have been selection over approximately the last three thousand years for women with broader hips.

The baby's head is the biggest challenge during childbirth:

Human birthing is difficult owing to a tradeoff between large neonatal brain size and maternal pelvic dimensions, which are constrained by aspects of bipedal biomechanics. The net effect is that human neonatal head size closely matches maternal pelvic dimensions, unlike in our closest living relatives, the great apes, whose pelvic dimensions are larger than neonatal head sizes. (Franciscus 2009)

Have female hips become broader over the past three thousand years because the birth canal has had to accommodate babies with larger brains? That hypothesis would be consistent with an analysis of ancient DNA by Michael Woodley of Menie and others, who showed that alleles for educational attainment gradually increased in frequency between 4,560 and 1,210 years ago in Europeans and Central Asians. That increase may have been due to gene-culture coevolution: as societies grew larger and more complex, the average person had to perform mental tasks that likewise became larger in number and more complex. Such an environment would have favored the survival and reproduction of individuals with higher cognitive ability. Mean IQ thus rose over time, as did cranial capacity.

On the other hand, Henneberg (1988) showed that cranial capacity steadily shrank from the Mesolithic to modern times, becoming 9.9% smaller in men and 17.4% smaller in women. His conclusion was based on a large sample: 9,500 male skulls and 3,300 female skulls.

So we have a contradiction. Perhaps cranial capacity didn't really shrink from the Mesolithic to modern times. Perhaps smaller skulls are more likely to decompose faster. The skulls we unearth would therefore be a biased sample, and this bias toward preservation of larger skulls would gradually increase for skulls that have been in the ground longer.

The problem of "preservation bias" has already been noted with respect to female and infant remains:

There are nearly always more males than females in skeletal collections from archeological sites [...]. This has been explained in part by the comparatively rapid disintegration of lightly built female skeletons.

[...] The burial records show that most of the people buried in the Purisima cemetery were either infants, children, or elderly adults. The skeletal remains excavated from the cemetery, in contrast, are predominately those of young adults. The underrepresentation of young children in the skeletal collection is most likely a result of the comparatively rapid disintegration of their incompletely calcified bones.

[...] If, on the other hand, infants or elderly people are more common in a skeletal collection from a recent cemetery than they are in an ancient one, much less can be inferred about differences in the original age structure of the two burial populations. Such a difference would be expected due to differential preservation, even if the age structures of the two burial populations were identical. (Walker et al. 1988)

The same preservation bias might cause an overrepresentation of larger skulls among older remains.


Arner, A., H. Reyes-Centeno, G. Perry, and M. Grabowski. (2020). Pleiotropic effects on the recent evolution of human hip circumference and infant body size. The 89th Annual Meeting of the American Association of Physical Anthropologists (2020), April 17  

Franciscus, R.G. (2009). When did the modern human pattern of childbirth arise? New insights from an old Neandertal pelvis. Proceedings of the National Academy of Sciences 106(23): 9125-9126.  

Henneberg, M. (1988). Decrease of human skull size in the Holocene. Human Biology 60: 395-405.  

Walker, P.L., J.R. Johnson, and P.M. Lambert. (1988). Age and sex biases in the preservation of human skeletal remains. American Journal of Physical Anthropology 76: 183-188.

Woodley of Menie, M.A., S. Younuskunju, B. Balan, and D. Piffer. (2017). Holocene selection for variants associated with general cognitive ability: Comparing ancient and modern genomes. Twin Research and Human Genetics 20: 271-280. 


Anonymous said...

Broader hipped, and broader waisted? What is the significance of the top image of the WHRs?

Anonymous said...

I do not understand too. WHR decreased from 0,9 to current 0,7? Or today's women have WHR 0,9 ?

Frank said...

3,000 yrs encompasses pre-Celtic, Celtic, Germanic and a bit of Norman and Roman thrown in. Are there differences from these cultures?

Peter Frost said...


Maybe I should change that image. It's misleading too many people.


We're probably looking at a change that happened throughout most of Europe.

Tyrion said...

Dr. Frost, I have 3 questions:

1) What's the correlation -according obstetric morphometric measurements- between hips circumference and birth canal, and the width and shape of the pelvis? If the correlation was not strong then it’d be inside measurement that counts, not outside. We won't able to known from the outside measurements what the internal space (birth canal) will be.

2) Have the referred studies controlled for skeleton height? Following an invariant allometric ratio, taller females may have absolute hip circumference diameters than shorter ones, even while maintaining relative height/hip ratios. Is the average height of the sampled female skeletons similar to the current female average population height?

3)Do you know of any study measuring morphological hips differences across populations? Based on this hypothesis of infant cranial size, we could deduce that East Asian women have greater pelvic girths (due to higher average Asian IQ) than European / Caucasian and African females. Anyway I get the vibe Asian women don't have especially wide hips, even I would go so far as to claim that African and European women seem to have wider hips

Peter Frost said...

Hi Tyron,

I've relayed your questions to Audrey Arner. I'll post the answers if she replies.

Anonymous said...

May 30, 2012
White Americans' heads are getting bigger. That's according to research by forensic anthropologists at the University of Tennessee, Knoxville

tomR said...

The biggest advantage of narrow hips is good mobility. Especially long distance mobility. Think long distance runners. And in the past people were organized in mobile tribes, that participated in lots of migrations. Also mobility as in dancing.

The advantage of somehow wider hips are:
- for men: potentially higher ability to lift heavy things. Eg deadlift champions have somehow wider hips than long distance runners.
- for women: giving birth, and lifting heavy things.

In more contemporary times the migrating tribes period was replaced by sedentary phase. Which in many cases was not even natural, but legal - eg. serfs bound to particular land, slaves held against their will on a particular farm, or even city dwellers that only had their craft licenses in a particular city, so they had to stay there.
As such none of these needed much mobility, so narrow hips became just a hindrance for both giving birth and lifting heavy things.

The only people that still migrated in later times were steppe tribes that rode horses, rather than moved on feet. So they also didn't need narrow hips.