Sleep Among Early Hominids (~2 million – 300,000 years ago) Tree sleeping: Our ancestors slept in trees, largely for safety from predators. This required light, fragmented sleep. Evolution of ground sleep: Homo erectus likely began sleeping on the ground, enabled by fire use for protection. Impact: Sleeping on the ground led to deeper, more consolidated sleep, crucial for memory consolidation and cognitive evolution, blood circulation and REM. "By improving sleep quality, early humans may have supercharged brain development—key for language, tools, and social learning." — Dr. Matthew Walker, Why We Sleep