simple, chance calculation over millions of years and billions of creatures!
or would your scientific reasoning point towards a 1600 year old book as scientific source!
Abiogenesis would be so unlikely that it verges on a religious doctrine.
No, its simple logical chance calculation Billions times billions times billions times billions times billions etc etc etc in a very hostile world. which makes it scientific speculation based on logic, observation and scientific sources. It can and has also be revised when other evidence or more feesible theories arise. It's how science works.
This is far from a religious doctrine where you bluntly have to follow the written words of a 1600 year old book, Don't dare to be critical about these texts, follow an old grey man orating or believe in an upper being in the sky controlling us all!
While definitely a plausible roadmap from light-sensitive spot up through progressively less primitive structures of eye, he is unfortunately glossing over the most important part.
Ultimately, all evolution happens at the molecular level, so this hazy roadmap needs to be extended further down into biochemistry. The process of converting light energy into a nerve impulse is bloody complicated, so the most important question here is: how did evolution produce the light-sensitive spot he oh-so-conveniently started with?