The whole 'half-human' part confuses me too. I get species that are not too far away from each other on the same planet/evolutionary tree being able to produce viable offspring, but two species on totally different planets that developed from completely different evolutionary trees? How does that work at all? How are their brain structures even remotely compatible? (Or any other major body systems? Do Betazoids just happen to have near identical circulatory, digestive, and reproductive systems to humans?)