Quick Answer. The function of motor neurons is to release the neurotransmitter acetylcholine, which are released at a junction known as the neuromuscular junction, that bind to postsynaptic receptors, causing the muscle fiber to respond and result into a muscle movement.
The critical element that culturally sets humans apart from other species is the functional superiority of the human brain. That existing human culture has three axial components, namely politics, religion, and technology, which influence the affairs of mankind, must be obvious to all with a passing interest in human behaviour.
The further apart two animals are in genetic terms, the less likely they are to produce viable offspring. At this point, humans seem to have been separate from other animals for far too long to interbreed. We diverged from our closest extant relative, the chimpanzee, as many as 7 million years ago. (For comparison, our apparent tryst with the Neanderthals occurred less than 700,000 years after we split off from them.).