Take what I say with an implied "all the evidence indicates that..." or "the most reasonable interpretation based on current evidence is that...". These are always implied in
anything said in all walks of life.
That's all speculation based on circumstantial evidence. You couldn't know that empirically because it requires the observation and testing of subjects. Its theoretical. Could it be true? Certainly.
Think of it this way: If you have an animal with a similar genome, similar morphology, similar everything, it would be easy to speculate that one comes from the other. But that's totally subjective, unless they both share genetic mistakes. Because at some point, two animals will share more similarities than another when comparing them. That in no way proves they were related to one another.
I won't go into the "historical subject" aspect of this but will just comment that we do experiments all the time. When we explore an new fossil deposit we are experimenting to see if we make certain observations.
One observation we have continued to make is that there were no cats and dogs 70 million years ago.
Now we observe cats and dogs.
So we need a theory of how they got here. What is yours? The consensus scientific one is that something or things alive then kept changing until it's or their descendants became cats and dogs. Do you disagree?
Then the question is: was it the same thing that became cats and dogs or different things? The consensus is that is the former. With lots of good evidence for it. With the amount of evidence available calling it "speculation" is a bit of stretch for the meaning of that word.
Separately, what to you mean by "circumstantial" evidence? What kind is better?
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