We propose to test a series of hypotheses indicating that there is a genetic basis for variability in various cortical features (including asymmetries) by using advanced computer technology to analyze endocranial casts (endocasts) prepared from 600 skulls of rhesus monkeys (Macaca mulatta) from Cayo Santiago. An endocast, or replica of the interior braincase surface, reproduces accurate details of external brain morphology including sutures, venous sinuses, shape, and cortical sulci. The Cayo Santiago skeletal collection provides a unique research opportunity because it is the only primate osteological collection in the world that is associated with known maternal genealogies, ages at death, 30 years of behavioral/demographic records, and numerous publications on the heritabilities of external aspects of the skull. In this study, we will undertake a computer analysis of all endocast and cranial data in order to estimate heritabilities and genetic correlations of cortical features, and to compare the genetic bases for variation in osteological versus neurological features. Prior studies of endocasts have relied upon simplistic two dimensional data acquisition techniques which have sometimes led to erroneous conclusions. However, to understand the morphology of the brain's surface, accurate measurements of the location, orientation, length and other parameters for anatomically significant features must be available in three dimensions. An approach for three dimensional analysis of endocasts is already available in specialized diagnostic medical imaging centers and in discrete manufacturing computer aided design facilities. Specifically, medical computed tomography (CT) scanners have been applied to the study of endocasts, and surface measurements have been made manually with a specialized 3-dimensional digitizer unit. The proposed research is based on a collaboration between uniquely qualified researchers at three Institutions who propose to use this advanced imaging and computer aided design technology which is being made available to the project without cost.