First of all, you need to understand what a theory is. It is a conceptual framework that ties together all of the known facts and properties of the system in question in such a way as to enable the scientist to make testable predictions.
In this case, the system is the biosphere, and the changes over time which have been observed for millennia.
The variety and diversity of life all over the planet is the biggest consequence of the processes which are conceptualized within the theory of evolution. The Gobi desert and the deserts of the western United States are extremely similar in climate and appearance. Yet the plants that grow in each desert are completely different. Without the theory of evolution, there is utterly no explanation of why the flora and fauna of each desert would be so different when the deserts themselves are so similar. If you believe that one of the versions of the creation story is a scientific document, rather than a morality lesson, there is truly no explanation for the diversity of life over the world. There is no explanation for the existence of any species that is not mentioned in the Bible, etc.
And so on and so forth.
“Without the theory of evolution, there is utterly no explanation of why the flora and fauna of each desert would be so different when the deserts themselves are so similar.”
Really? Seems like a pretty big leap of faith to assert this.
That’s not what I asked.
I asked for an example of a single scientific fact for which the theory of evolution is a necessary ontological foundation.