Agriculture Reference
In-Depth Information
are rare. In other words, if orthodontists were to travel back in time, they would find
themselves with very little to do, at least with respect to fixing crooked teeth.
What explains this rapid growth in the incidence of malaligned teeth in the mod-
ern world? The answer appears to lie in the relationship between tooth size and jaw
size. Tooth size has a much higher heritability than jaw size. That is, the teeth have
a greater genetic component than bone. Teeth have decreased in size, but not nearly
to the extent of bone (jaw) size in the last 10,000 years. This disjunction in reduction
of tooth and jaw size has resulted in a kind of disharmony between the teeth and the
supporting bone. That is, people have more crowded teeth today than in the past, at
least in part, because of the greater reduction in the size of the jaws than in the size
of the teeth. By all accounts, our diet is continuing to get softer. Thus, the incidence
of malocclusions will likely continue to grow. Orthodontists will enjoy job security
for the foreseeable future.
tRAde-offs And tRAnsfoRmAtIons:
settIng the stAge foR the PResent
The skeletal record from past human populations shows a similar story of a general
decline in health in early agriculturalists relative to their foraging predecessors. But,
this is not to leave the impression that the shift was a full-blown disaster—far from
it. On the negative side, there is clear evidence of increased infections and poorer
health generally. However, in nearly every place where humans made the shift to
agriculture there was a dramatic increase in population size, largely shaped by
increase in birth rate (Bocquet-Appel and Naji 2006). This remarkable demographic
transition is now well documented in the archaeological record, from European and
North American settings especially. Importantly, this transition is an evolutionary
success story in increased numbers and in those who survive to reproductive age.
New genetic evidence indicates that this rapid increase in human population has also
resulted in increase in human adaptive evolution in the last 10,000 years, far more
than once thought (Hawks et al. 2007).
Agriculture provided the economic context for the rise of civilization and eventu-
ally the technology that we currently enjoy. The downside, of course, is that large
population and its concentration provide the essential breeding ground for the main-
tenance and transport of pathogens from host to host, eventually infecting many
thousands, if not millions, of people. Examples in recent history abound, such as
the 1918 influenza epidemic that resulted in the deaths of millions globally. Today,
we are seeing an alarming increase in new infectious diseases, fueled by population
increase and human-to-human transfer of rapidly evolving pathogens. In addition,
some of the old diseases have reemerged, such as tuberculosis, resulting in the deaths
of some 2 to 3 million people a year.
The biological challenges facing humans in the early twenty-first century have their
roots in the agricultural revolution of the Holocene. There are many lessons in the
record that I have described in this chapter. Key among them is that a large and dense
population provides the basis for infectious disease and its spread. If we are to set a
better course for the future, it will be essential to get the staggering growth of our
