Final answer:
A major increase in brain size, or encephalization, occurred between about 800,000 and 100,000 years ago, expanding from 600 cm³ to 1400 cm³. This growth was likely influenced by climate change and the need for more complex cognitive abilities. Adolescence also sees significant brain development, with synaptic pruning and myelination increasing the brain's efficiency and functions.
Step-by-step explanation:
The major increase in brain size in human evolution occurred relatively rapidly between about 800,000 and 100,000 years ago. During this period, we saw encephalization, or brain growth, where the average brain volume expanded from approximately 600 cm³ to about 1400 cm³. This significant growth coincided with the appearance of the earliest Homo sapiens. Scientists have proposed that the changing climate and the demands of a more unpredictable environment pushed for a larger, more capable brain. This evolution of brain size facilitated advancements in culture and technology, enabling our ancestors to thrive across diverse habitats.
Cognitive development doesn't stop with brain growth in volume; it also involves synaptic pruning and increased myelination during adolescence, which leads to an increase in the efficiency and functionality of the brain. No longer just larger in size, the adolescent brain is more complex and better adapted for high-level cognitive functions. Moreover, a decrease in the size of the jaws and an increase in the size of the cranium contributed to a change in the physical structure of the skull, accommodating the growing brain.