How can people naturally become smaller?
Over the course of Homo-sapiens, we have become larger, because of diet & selection. Even in the last couple centuries. Today, we vary across geography and cultures, too, of course.
Now it is thousands of years in the future (your call) and people live happily on Earth, but have evolved to be much smaller; still in proportion, just smaller even than our distant ancestors. We've grown in population, but have stabilized the Earth's issues and become highly sustainable: almost Utopia.
What contributing factors helped make us so much shorter over time - even those staying on an Earth?
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1 answer
Parents don't want their kids to die of cancer or diabetes. Nor do governments want to spend billions treating these conditions. Laron dwarfism is a genetic condition that causes the growth hormone (GH) receptor to work less efficiently. The resulting insensitivity to growth hormone, or "GH resistance", confers nigh immunity to cancer and type 2 diabetes and reduces the harmful effects of aging.
Based on other answers, I can think of a couple ways that the Laron allele might be selected for.
- Genetic screening for the Laron allele could become popular. Parents could arrange marriages to Laron dwarfs, or governments could provide tax breaks or health insurance subsidies to families with at least one Laron parent or two Laron carriers. In the limit, Gattaca-style recombinant "designer babies" would have the GH receptor gene corrupted on purpose to the Laron genotype.
- A more carcinogenic environment would cause a population crash, giving Laron dwarfs more chance to survive (make your time) and reproduce. So might the diabetes-prone high-calorie, high-carbohydrate Western diet.
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