Are you suggesting that, over the 7000+ years, humans have only just now figured out how to cook chicken properly?
About 150 years ago they threw a doctor in an insane asylum for suggesting to wash hands between patients and until fairly recently no one used meat thermometers. So yes. They didn’t have a bead on it 100 years ago.
You don’t need a thermometer to cook chicken.
You cook it and taste it.
Was it raw? Was it tough? You cook it slightly longer or shorter next time.
People didn’t have microscopes hundreds of years ago, but they were as intelligent as we are.
And you don’t need to understand germ theory to know what tastes good.
The fact that you’re even entertaining this is ridiculous, and I refuse to engage further.