- Laura Spinney is a science writer whose work has been published in The Economist, National Geographic, Nature, New Scientist and The Telegraph, among others. Her latest book is Pale Rider: The Spanish Flu of 1918 and How it Changed the World (2017). She lives in Paris, France.
- While this paper has to do with Twinning, it has little to do with my Thesis.
- The paper explains how the rates of fraternal twinning vary from 0.7% to 2.8% depending on time period and geography, while the rate of identical twinning stays fairly constant – for all mammals, other than armadillos, apparently – at 0.4%.
- There are two interesting-sounding papers cited:-
→ Pison - Twinning Rates in Developed Countries - Trends and Explanations
→ Pison - The Frequency of Twin Births in France - The Triple Influence of Biology, Medicine and Family Behaviour
I’m unlikely ever to have time to read them, so I’ve saved – but not logged – them.
- The frequency of fraternal twins – at least in natural conception – depends on multiple ovulation. In turn, this depends on certain hormones, which in turn depends on age. It seems that multiple ovulation is more likely if the woman is in her mid-thirties. The percentage of relatively late births depends on social conditions, birth control and society’s tolerance of single parenthood.
- The situation is complicated by IVF. In the early days – where multiple embryos were implanted for reasons of ‘insurance’ – twinning increased, but these days the technology has improved (including inspection of pre-implantation embryos to ensure health and viability), so twinning has decreased again. It is noted that IVF is unpopular in sub-Saharan Africa both on the grounds of expense and of the general risk to life for both mother and baby.
- Sub-Title: "The proportion of twins in the population has waxed and waned in human history. For the first time we understand why"
- For the full text see Aeon: Spinney - The twin boom.
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- Blue: Text by me; © Theo Todman, 2022
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