The left planum temporale is found to be larger than the right in the brains of infants, adults, and some non-human primates (chimps and gorillas). In infants, this asymmetry can be seen in a variety of genes as early as 12-14 weeks of gestation. Additionally, Broca's area (a zone responsible for speech) is larger on the left than on the right for these groups. For monkeys, the left hemisphere is activated more when hearing monkey vocalizations, similar to humans with speech.