... but they are claims ...
Many people have dismissed these hypotheses as speculative, and with that, they dismiss the research, the issue and the suffering of the people on the ground. What these naysayers fail to understand is that hypotheses are always speculative to a degree – they are informed, but they are claims intended to be verified or falsified. This is the nature of the scientific method. First, you observe certain phenomena in the world, then you come up with a hypothesis to explain those phenomena. Then, you conduct an experiment to test your hypothesis.
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Does the underlined part make sense? Could their claims or there are claims work better?
Re: ... but they are claims ...
NOT A TEACHER
I'd use "they", which refers to "hypotheses". The original sentence looks OK to me.