ROOTS OF MODERN THINKING. “Much of our previous understanding of mimetic musculature and its evolution in primates was rooted solely in phylogeny. Huber (1931) held that facial expression musculature was the simplest and least complex in prosimians (complexity here referring to number of individual muscles, relative sizes, interconnections, and attachment sites).”
http://onlinelibrary.wiley.com/doi/10.1111/joa.12440/full