From Harvard Magazine:
Daniel Lieberman tracks the evolution of the human head:
“The head presents an interesting evolutionary paradox,” explains Lieberman, chair of the new department of human evolutionary biology, “because on the one hand it is so complicated that if anything goes wrong, the organism dies. On the other hand, it is where natural selection can and has acted powerfully to make us what we are.” Everything is closely connected. For example, the roof of the orbits is the floor of the brain—if one changes, they both do.
“How is it,” he asks, “that something so complicated and so vital can also be so evolvable?” One explanation involves modularity and integration. Not only do heads contain many modules (instructions for building an eye to see, for example, or an ear to listen), but each module is itself “intensely integrated in terms of development, structure, and function….Changes to the size, the shape, or the relative timing of development of each of the head’s many modules offer a variety of opportunities for change.” Studying the head’s modules, Lieberman writes, may help us understand why “the human head has changed substantially since our lineage diverged from the chimpanzee’s lineage.” It also provides an opportunity for “exploring how nature tinkers with development in ways that affect function and permit the evolution of complex structures.”