Final answer:
The consumption of cooked meat provided the essential proteins necessary for the enlargement and development of the human brain, particularly the frontal lobe. The primary germ layer responsible for the central nervous system's development is the ectoderm.
Step-by-step explanation:
The material that provided crucial proteins for brain development in humans was meat, which became a significant part of the diet especially following the control of fire. Fire allowed for the cooking of protein, which made it easier to digest and more nutritious as compared to eating raw meat. As humans consumed more cooked meat, the increased protein intake is believed to have been crucial for the evolution of our brain, particularly the development of the larger frontal lobe, which is associated with advanced cognitive functions like empathy, problem-solving, and social intelligence. This development was a key factor in the evolution of human society and cultural practices such as storytelling, art, and the establishment of rules within growing communities.
Regarding the primary germ layer responsible for the development of the central nervous system, it is the ectoderm. Specifically, the neural plate—which is derived from the ectoderm—eventually forms the neural tube, the precursor to the central nervous system.