Final answer:
Most brain growth in hominins occurs after birth, partly because of the size constraints of the birth canal. Encephalization, which refers to the increase in brain size in the genus Homo, can be linked to various factors including adaptability to climate change and the development of culture and technology.
Step-by-step explanation:
Most brain growth in hominins occurs outside the womb. This is due in part to constraints of the birth canal size; the brain must fit within the confines of the skull, which in turn needs to pass through the birth canal. However, once born, the human brain continues to grow and develop rapidly during early childhood.
Several hypotheses exist for the notable increase in brain size, commonly referred to as encephalization, in the genus Homo. Some of the explanations for this rapid brain expansion, which occurred particularly between about 800,000 and 100,000 years ago, include adaptive responses to rapid climate change, and the concurrent development of culture and technology.
Encephalization correlates with increased behavioral, cognitive, and cultural complexity seen in human evolution. Homo habilis, which had a cranial capacity significantly larger than that of chimpanzees, is a good example of early hominin brain growth. The intelligence evolution journey continued with Homo erectus and later species, culminating with Homo sapiens.