Every living thing descended from a common ancestor over millions of years.
This seems like a simple, stable fact, but is it really?
Addressing it firstly in purely scientific terms.
First of all there are some obvious problems with the statement as it stands. When you say "every living thing" I assume you probably mean every living thing on Earth. You don't intend to rule out the possibility that life arose in different parts of the universe and don't share a common ancestor.
But even if we confine ourselves to this planet it is still presuming a lot. As extensive as our knowledge of life on earth is, is it really out of the question that, deep in the ocean, or in some other inhospitable habitat, life has arisen separately from the rest of life on Earth? Some may say it's unlikely, but I don't think many scientists would rule it out.
And there are philosophical problems with the statement too.
In a sense even a creationist could agree with the statement, since they believe that God is the Father of all living creatures.
The you might want to qualify "ancestor" through reproduction of one finite living thing from another.
Of course Darwin himself famously left open the possibility that God gave life to a few original creatures, or just one, and that evolution took over from there. So Darwin himself wasn't necessarily dogmatic about this supposed central "fact" about evolution.
Since Darwin's time scientists have scrutinised life on our planet an concluded that all life on Earth has a common ancestor and that evolution does not have multiple starting points. There are apparrently good reasons for drawing this conclusion. But is it out of the question that new discoveries will undermine this conclusion and that in fact life on Earth had multiple starting points. However unlikely you think it might be, it would be unwise to say it's impossible.
Plus all of this assumes a purely materialist conception of reality to begin with. How can we know that what appears as physical beings with causal and reproductive relations to one another is not the result of a mind that is external the reality as we see it? Strange and weird idea? Well yes. And there are many things about reality that are strange and weird. Frankly if the material universe is all that there is, all reality can be explained by the process of natural laws, and humans are the most intelligent beings ever to arise. Then frankly that's pretty weird and mysterious. No less miraculous that the explanations offered by many religions