Stuttering
Features developed later in evolution are usually more variable than features developed earlier. The classic example of this principle is the difficulties of many human births compared to the reliability of ape births. Languages in hominids is certainly one of their later accomplishments.<ref>Murphy E. & Benítez-Burraco A. 2017. Paleo-oscillomics: inferring aspects of Neanderthal language abilities from gene regulation of neural oscillations. Journal of Anthropological Sciences'. 96: 111–124.</ref>