Building a face
Making a face depends on a remarkably complex process of cell migration and differentiation
The face accommodates some of our main sensory organs – eyes, ears, nose, mouth, skin. Yet the human face is not just a scaffold for these organs. It has come to take on a role of its own, supporting social communication between individuals.
The face is a key part of our individual identity. We lavish attention on our own faces and scour the faces of others for indications of their mood and personality. For example, eye tracking studies show that we pick angry faces out of a crowd faster than happy faces – maybe because there is an evolutionary benefit in terms of spotting threats.
Mammalian development must be one of nature’s most extraordinary processes. Early on the embryo is tube-like, with the beginnings of the spinal cord running along its back – the neural tube. At the front end of the neural tube (the neural crest), a population of stem cells multiply and swarm off in huge numbers to distinct locations, forming almost all of the skeletal, muscular and neural tissues of the head.
The human head is thus precisely sculpted by the mass migration, multiplication and differentiation of cells. How is such precision achieved?
A crucial point is whether an individual cell leaving the neural crest already ‘knows’ what it is destined to become, or whether its fate depends on where it finally finds itself. Migrant workers might know they are going to Australia, say, but do they already know they will be teachers when they leave, or will they decide what to do when they arrive?
The answer is probably a bit of both: a departing cell is already committed to becoming something specific to some extent, but still receives crucial input from the cells it encounters in its final location (see Genes and body plans for more).Lead image:
Illustration © Glen McBeth