[laksjd]

Short answer: They didn't survive. IIRC a significant portion of all humans born in past centuries simply died as infants/children, usually from things that are trivially preventable today with basic hygiene, good nutrition and antibiotics/vaccines.

Humanity as a species obviously survived because people simply had a lot of children to compensate the high mortality rates.

[SFJulie]

well, I beg to differ, and quite a lot.

I am a mover educated with a master in physics.

My father is a physician.

a Physician - physicist talk looks like this :

Dad, medical studies are not science ; for instance fat are goods, then bad then good again.

Son, Newton laws have been proven wrong by Einstein

Dear dad, Newton laws are still valid in the right domain, something proven wrong may be proven wrong at the edge but not in its core, if medecine was science, fat would always be good most of the time, except when ...

Yes, but we medics invented meta analysis that made the science better

You are mainly comparing apple and potatoes without blinking, and you are surprised the results of your studies are hardly reproducible.

Long story short; hygienists are leading medical science based on their religious believes (like Pasteur with alcohol) and believes are hardly a good way of leading studies, and I am used to live every day with a tenant of as soft science as psychology/philosophy/history that has a diabete type II for believing in the BS of his fellow «scientific» colleagues, and I do not know if I am angry or laughing.