Recent comments in /f/askscience

the__itis t1_jactczc wrote

It would seem to me that current climate conditions at the time of birth would change survivability rates dynamically.

Higher survivability rates should equate to a higher ratio of females as they would subsequently reproduce the overall population in higher numbers.

I believe mammals (Great apes specifically) have a similar “quirk” where older male age and higher average calorie diets lead to more female births.

2

AMartin223 t1_jaco2pt wrote

I think the main reason for that mindset is that we have these various documented syndromes like described above where failures to emit certain hormones prevent the transition to male anatomy, so it feels more like the female path is the default rather than a different fork in the road. It seems though that describing the early stages either way can be a correct model.

8

hananobira t1_jacni22 wrote

Other way around. Mothers are more likely to have daughters when the food supply is low. Females are hardier, are more resistant to famine and disease, and live longer. Mothers are more likely to have sons when they are living in plenty, because sons are less likely to survive childhood and require greater resources to grow taller and stronger.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2602810/

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3367790/

https://www.cambridge.org/core/journals/continuity-and-change/article/abs/famine-and-the-female-mortality-advantage-sex-gender-and-mortality-in-northwest-england-c-15901630/8D3B5297ABD8AFEAAFF9FA52923AE5F1

https://www.sciencedaily.com/releases/2011/09/110927192352.htm

4

paroya t1_jacm0kh wrote

certain swordtail population can do a female to male change later in their life.

medaka (oryzias latipes) have about a 100% male exclusive hatch rate at 34°, starting from 27° and going up from there.

on topic of swordtails, there is a related species (amazon molly) which is unique in that it is the only known stable all-female species, reason so far unknown afaik.

in case anyone wanted to google papers.

1

kmoonster t1_jaclwiu wrote

You know how a sidewalk, driveway, etc will get grass and trees in the cracks that you have to clip? And how the edge of the grass can creep over the edge of the concrete, meaning the sidewalk occasionally has to be edged to keep it clear? Same thing, but with a lot more time.

Worth adding that cultures would often knock down old buildings and just level the remnants, then put the replacement building right on top of the older one just a foot or two higher than the predecessor. Many of these are the big mounds you see that are listed as archeological sites.

Combine these two for generation upon generation, and you end up with ruins buried anywhere from a few centimeters up to several meters under what we now call ground-level.

Of course, wind and water can move dirt in -- and they can remove or erode it as well.

1