Feel free to post perspectives or questions in the chat at any point!

Africa is not one place, and has populations displaying the greatest genetic variation within our species, plus considerable environmental variance, so no surprise on the range of rates.

Is CPD lower in areas of malnutrition/food insecurity? With less food, perhaps smaller infants and less CPD.

Of course, malnutrition could have proportional effects on adult females, so no reason to suppose that malnutrition reduces this problem.

@Elizabeth Often lower birthweights but malnutrition during development can "flatten" the pelvis and leads to greater problems esp in younger women (e.g., teens) who haven't stopped growing

I wonder whether you can predict problems by disparity between parent size: if the father is significantly larger as an adult than the mother, is there more likely to be a too-large baby? And, vice versa, do more similar sized females/males (or couples where the female is larger than the male) have less problems? Or do foetus sizes not reflect adult sizes?

Jonathan Wells wrote an interesting paper about this looking at ethnically-mixed partnerings: South Asians and Europeans

disparity between parent size: This might be a reason behind assortative mating.

I agree about the impact on malnutrition on growth of pelvis during female development. Best solution is infants who are not LGA and well-nourished mothers.

It's interesting, because if there's selection on larger mothers to prevent problems in childbirth, there must be stronger selection on larger males (e.g. sexual competition)?

“Ethnically-mixed” pairings in this regard would only have relevance if the populations in question are different in their mean sizes. Also, as ethnicity refers to common national origin and culture, that is not the appropriate term to use here when the real issues is potential biological variation between populations. For example, a pairing between a German of European descent and French person of European descent is an ethnic mixture as well.

There is some genetic data supporting an association between maternal height (body size) and birth size (and gestational age): https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4540580/

The Wells et al paper about S Asians and Europeans was predicated on the info that birthweights were v different between the two populations so not done randomly as I understand it

Does the model take into account the difference in size between boys and girls?

So this would mean sexually antagonistic genes.

I would frame it in terms of parent-offspring conflict rather than sexual antagonism

If genes favoring larger D are selected for in males, but selected against in females, seem to fit the sexual antagonism definition.

But the fetuses are both males and females. The selection is not in the father but in the fetus.

Agreed that selection acts on the fetuses, but those fetuses contain genes that came from their parents (female/male), so antagonism is not acting differentially in development, but on parental fitness. However, I think this distinction may really be a minor point.

There are two paternal genes in the father but only one in the fetus. It is not the same thing. I have distinguished between parental antagonism and sexual antagonism.

So does “White” here mean persons of European descent, if so best to say that than use social definition.

I agree that this is some kind of parent-offspring conflict, but only for those individuals above the “fitness cliff”

Agreed. Going over the cliff is in nobody’s interest

Hi everyone. Can anyone please tell me what is ultra-male and ultra-female?

ultra is simply an exaggeration of the difference to make it more obvious

@Philipp, given that many women in the global north have unnecessary C-sections and many women in the global south who might need one can't get one, how does that affect your model that C-sections might affect selection in the future?

I think this is simply referring to the most exaggerated forms of male and female pelvis.

Thanks

We’ll be opening up for discussion soon! Feel free to virtually raise your hand at any point to join the queue. (Click “Reactions” at the bottom of your screen, then “Raise Hand.”)

Meredith, for some reason my Zoom is not showing the Reactions for this session but I would like to ask a question

For the evolutionary dynamics, only the C-sections that did save lives matter, not those for other reasons.

Thank you

@Philipp: in reality that might be very few then...

agreed

Philipp, do you expect that c-sections are a temporary medical solution and that relaxed selection will lead to a new equilibrium where there is a new cliff?

Fetal size cannot increase a good deal more because of the metabolic capacity of the mother, among other reasons. Also, medical advancements in neonatology and pelvic floor treatment reduce selection for large newborns and a narrow pelvis. Hence, the trend we described certainly has a limit and may have lowed or stopped already.

We have time for a couple more questions before we close! Feel free to post in the chat or raise your hand.

One idea: male pelves aren't packed with as much stuff and that the pelvis is more like the cranium than we realize. Big brain = big skull. Presence of uterus, vagina, clitoris = big pelvic canal

I’m curious if and how much of the variation in pelvis shape between males and females is a byproduct of other developmental differences between Ms and Fs rather than a direct product of selection (ie., a spandrel)?

I wrote about that, Vinny: https://onlinelibrary.wiley.com/doi/abs/10.1002/evan.21834