What were the three key observations made by darwin that allowed him to deduce that natural selection is a primary driver of evolution?

The three observations

number of adults in a population tends to remain the same over time even though, for most organisms, parents tend to produce multiple and sometimes many offspring.

variation exists among members of populations.

and finally, individuals having variation that is advantageous for survival and reproduction increase in relative frequency over time.

The hawk receives 0.1% energy from the caterpillar although the caterpillar gets eaten by another bird smaller than the hawk first

Photosynthesis. . .