Human evolution theory utilizing concepts of neoteny & female sexual selection
An etiology of neuropsychological disorders such as autism and dyslexia, and the origin of left handedness.
"The proposition is simply that the language (or perhaps rather 'proto-language') that was spoken probably lacked certain elements typical of fully developed human languages today. We might propose that such proto-languages lacked at least tense-modality-aspect systems. Probably they also lacked the ability to form clauses, and hence displacement, in discourse. These are the elements that were proposed above as essential to such features as the elaboration of extended kinship systems, communication beyond face-to-face encounters and exchange of information beyond the here-and-now, the organization of logistical economic strategies, and the extension of the time depth of adaptation to environmental fluctuations. Therefore, all of these organizational features may be proposed to have been absent as well, leading to the 'blocking' of human populations in this period from colonization and long-term occupation of both tundra and desert environments." (Whallon, Robert (1989) The Human Revolution. (P. Mellars & C. Stringer eds.) Princeton Univ. Press: Princeton p. 451)