People used to have kids regardless of whether they wanted them; now there is selection for wanting children, which is correlated with being loving parents.
Hey, look at ATP synthase with me for a second. It’s literally a molecular rotary motor with a crank shaft, embedded in a membrane holding a proton reservoir. (In eukaryotes like us, that membrane is the inner mitochondrial membrane; in prokaryotes it’s usually the inner membrane of the cell.
If your mother experienced a famine while you were a third trimester fetus, this messes up your metabolic programming and increases your risk for metabolic diseases – in ways that can cascade down to your own children epigenetically. During their occupation of Holland in 1944, the German administration placed an embargo on food transports to punish the locals for a railway strike.