Do these sound natural?
Based on his incomplete research, John conjectured that people themselves are responsible for the conditions they are in.

The scientists surmised that marijuana is responsible for everything despite not having evidence.

Question

Do these sound natural?
Based on his incomplete research, John conjectured that people themselves are responsible for the conditions they are in.

The scientists surmised that marijuana is responsible for everything despite not having evidence.

Answer

The first is ok, to my mind.  Maybe I'd add a word or two 'Based on his own admittedly incomplete research ...'
The second mmmm 'not having' is awkward - how about 'despite the lack of supporting evidence'?

Answer

You're a native English speaker, right? Yes, they sound perfect. ;)

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