Excited to listen to this episode, but I disagree that Darwin's theory can't be decisively tested (as much as Newton's).
I'd highly recommend the book 'Why Evolution Is True'. It describes how Darwin, and others, made a lot of predictions that were verified, with many different lines of evidence – including fossils, vestigial structures, biogeography, molecular evidence, natural selection in action, and speciation.
Darwin was a great interlocutor but many of these predictions were tested in his work, or during his lifetime. And some of his auxiliary hypotheses did not hold up, and helped refine the theory. Anyway, it's a great book!
The Origin of Species was published in 1859. Principia Mathematica was published in 1687, two centuries earlier.
Conceptually, it seems like natural selection is much simpler than the theory of gravity. So why did it take two centuries longer to discover?
A contemporary of Darwin's, Thomas Huxley, read the Origin of Species and said, “How extremely stupid not to have thought of that!” Nobody ever said the same for not beating Newton to the Principia.
I wonder if the reason this happened is that Darwin’s cannot be decisively tested. The evidence is circumstantial, retrospective, and cumulative. There's no equivalent of Newton running the numbers on the moon's orbital period and radius, and confirming that it corresponds to his theory.
In fact, nearly two thousand years before Darwin, the Roman poet Lucretius argued in De Rerum Natura that organisms suited to their environment survive while ill-adapted ones perish. But nobody built a science on it. Without a tight verification loop, the idea just floated by.
Terence Tao argues that Darwin succeeded where Lucretius failed because he had the ability to convince people that the gaps in his theory (specifically, what is the mechanism of heredity) would be filled.
This was less about ‘hard’ scientific insight, and more a matter of having good research taste and being persuasive. But it was crucial for progress in biology.