Final answer:
The evolution of large brains in our ancestors may have been influenced by the need to adapt to rapid climate change, the development of culture and technology, and dietary changes according to the expensive tissue hypothesis.
Step-by-step explanation:
Three possible selective factors underlying the evolution of large brains in our ancestors include climate change, the development of culture and technology, and dietary shifts related to the expensive tissue hypothesis.
Firstly, the period between 800,000 and 100,000 years ago was marked by rapid climate change, which may have demanded more complex neurological capabilities for survival, leading to encephalization. As the environment became less predictable, having a bigger brain aided in adapting to new challenges and exploiting different ecological niches.
Secondly, alongside biological evolution, there was a parallel increase in cultural sophistication and technological advancement. These were key behavioral adaptations that relied on cognitive abilities provided by a larger brain, allowing for the development of tools and technologies for survival and environmental management.
Lastly, the expensive tissue hypothesis suggests that as our ancestors' brains grew, they required more energy to function. To accommodate this, our digestive systems evolved to become smaller and more efficient, better suited for processing high-quality, nutrient-dense foods like meat, thus supporting the metabolic needs of a larger brain.