Final answer:
The social brain hypothesis explains that human brain size increased due to the complexity of social interactions rather than tool use. Increased brain size and cortical foldings within the cerebral cortex correlate with high intelligence and complex social behaviors, aiding survival and cultural evolution.
Step-by-step explanation:
The social brain hypothesis states that our brains are bigger because of the complexity of our social interactions, not for tool use. This hypothesis is supported by the evidence that primates, including humans, have a larger cerebrum, which allows for higher levels of intelligence and the development of complex social behaviors. Our cerebral cortex is particularly large and folded, enabling increased surface area which correlates with intelligence and social complexity. It appears that these cognitive abilities, fueled by our big brains, were essential in helping our ancestors adapt to rapid climate change and a more unpredictable environment around 800,000 to 100,000 years ago.
Moreover, having a larger brain enabled the evolution of culture and technology, contributing to the success of our species across varied habitats. While a larger Neanderthal brain (1,520 cc) could suggest greater intelligence than modern humans (1,200-1,400 cc), the difference in brain organization and emphasis on different anatomical areas could mean that intelligence manifested in different ways essential for survival. For instance, Neanderthals had a more developed back area of the brain related to sensory processing, likely advantageous for their challenging living conditions.