This chapter examines myelination data as an estimator of neural maturity because more comparative data exist for myelination than for other neural maturational parameters. It describes myelination and other neural maturational parameters in humans, rhesus monkeys, and other animals. Sequences of myelination are similar across species and nearly identical in rhesus monkey and human. The chimpanzees' activities with objects were recorded on audiotape at the time they occurred and compared to Piagetian analyses of object manipulation in human children. The extreme dependency of human infants raised under modern cultural conditions tells people nothing about the neural plasticity or learning capacities of human newborns as compared to ape newborns. The brains of newborn precocial mammals and birds such as guinea pigs, sheep and white leghorn hens are well myelinated at birth. Increased human intelligence relate to other factors such as increased brain size or differential neural organization. Cross-species similarities of neural developmental sequence imply cross-species similarities in behavioral development.