Making faces

Faces are weird. They really are largely accidents of development — all the fine features that we consider lovely sculpted signifiers of beauty are really just products of developmental processes, and what we recognize as pretty is actually just a good job of assembly. I’ve been talking about this bizarre way the human face is built for many years, especially since my interest in teratology means I spend a fair bit of time looking at cases where the assembly goes drastically wrong (in fish, not people; I can make things go wrong in fish embryos in ways that would send the mob after me with torches and pitchforks if I did them to human babies). Here’s what your face looked like, once upon a time.

Drawings of the developing human head and face between the 4th and 5th week (adapted from Nelson, 1953). The top row are side views, and the bottom row are face views of the same stages. The face develops from extensions and fusions of the pharyngeal arches, structures which are found in all other vertebrates, and which are modified in different ways in different species. Abbreviations: m, maxillary process (upper jaw); j, lower jaw; h, hyoid; n, nasal pit.

See what I mean by weird? Embryonically, much of your face was constructed from these plastic bars of tissue called pharyngeal arches, which extend to meet at the midline and then fuse and shift in complicated ways to form the familiar face we see in the mirror.

Now, even better, the BBC has created a simulated time-lapse video of face assembly. There are patent rules to how these tissues move, and common birth defects, like cleft palate, are a consequence of simply understood errors in how these tissues come together in the midline.

The article makes the point that the characteristics of facial development are also relics of our fishy ancestors. I guess it’s a good thing I study these phenomena in fish, after all, in addition to benefit of not enraging the local peasantry.