In this study, the roles of MCPH genes in the evolutionary enlargement of human brain size was explored through molecular evolutionary analysis of eight newly identified microcephaly genes; CEP135, ZNF335, PHC1, CDK6, SASS6, MFSD2A, CIT, and KIF14. Sequence data from 48 eutherian species was employed to investigate the signatures of episodic positive selection and diversifying selection during mammalian evolutionary history. The gene discussed is SASS6; the disease is microcephaly.