@ThePainefulTruth Said You argue against yourself. Abstract language leads to the ability for greater abstract thought, no?
No, I am not arguing against myself. Prior to the abstraction of thought, two things must occur. Firstly, the brain must be developed at a level capable of abstraction, and second, language must evolve to the point to allow for that abstraction. In other words, the ability for abstraction is a product, not a cause, of an advanced brain.
All human cultures have incredibly complex language, and this ability for amazing abstraction. Yet, when human groups split, our language was rudimentary (in fact, it could be argued that language did not even exist in any meaningful sense). If our brains were already capable of complex abstraction at that time, without anything more than basic words to express simple ideas, then, sexual and natural selection both lack any explanatory power. Neither of them can provide an adequate hypothesis.