It’s avoiding bad outcomes. Babies from closely related people often have problems. Practically every culture has a method of avoiding close relatives breeding
Eugenics is about breeding for desirable qualities, a eugenicist’s ideal person still couldn’t make good kids with a close relative
CO binds to haemoglobin (the oxygen carriers in your blood) just like O^2, but a little stronger. Effectively each molecule of CO puts one haemoglobin out of action, making you less able to transport oxygen out of your lungs