The answer is - hypothesis.
In here we have a situation where the scientist has be observing a certain behavior of the snakes under certain conditions. So he has some basis for proposing it as new exciting discovery, but the evidence are still basic ones and further investigation is needed.
Considering the definition for what is a hypothesis - ''a supposition or proposed explanation made on the basis of limited evidence as a starting point for further investigation'' - it perfectly fits the given scenario.
There is quite a lot, but the fact that both mitochondria and chloroplasts have their own circular DNAis what I would call "key" evidence. That is, these organelles are not "manufactured" by the cell (i.e., there are no "genes for mitochondria" in eukaryote genomes): like their ancestral bacteria, they reproduce by binary fission.
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