On the shoulders of biology’s giants
So far, they have not succeeded. But in biology, it has happened three times.
A theory is a definitive model of reality, which not only describes the facts, but predicts the outcomes of experiments yet to come.
One of the first was "cell theory". In the late 17th Century a Dutch draper, Antonie van Leeuwenhoek, first saw living cells with a lens designed for looking at cloth.