Introduction: What Are Humans Adapted For?

The introduction follows the escape of the “Mystery Monkey” from a zoo in Tampa, Florida in 2012.  The monkey had evaded capture for three years until he was captured in October 2012.  People marveled at the fact that a monkey was able to survive for so long in a city, a place where monkeys clearly do not belong.  However, Lieberman makes the point that humans are just as out of place in cities as a monkey.  Humans evolved as hunter-gatherers, and lived in groups of no more than 50.  This leads to the question, what exactly are humans adapted for?  And what does this mean for how humans should live today?  Some have attempted to live a more Paleolithic lifestyle, by avoiding processed foods and exercising regularly.  However, Lieberman makes the point that just because we evolved to eat certain things doesn’t mean they are good for us, or that there aren’t better options.  Additionally, not every trait is considered an adaptation, because not every trait is advantageous.  It’s important not to assume that particular traits are advantageous without evidence, even if the idea is intuitive.  Adaptations are driven by environmental factors, and always involve compromise.  Lieberman gives the example that for humans short legs are advantageous for conserving heat in colder climates, but makes walking and running less efficient.  It is impossible to evolve into a “perfect” organism because of the nature of adaptations.  Most importantly, humans did not evolve to have long, healthy lives.  Instead, humans evolved to live long and healthy lives, but only if this produced more surviving offspring.  Lieberman answers the question of “What are humans adapted for?” with a short answer of to have as many children as possible.  But in reality, humans are not adapted for any specific diet, habitat, environment, or exercise, and there is no such thing as optimal health.

However, one consequence of our evolutionary hypothesis is the mismatch hypothesis.  Adaptations that were once advantageous, such as craving energy rich foods and efficiently storing calories as fat, are now detrimental to our health in modern society.  When these adaptations work against us, it results in chronic diseases, such as diabetes.  The mismatch hypothesis is the focus of the second half of the book.  However, to fully understand the reasons for modern chronic illness, one must understand what humans are adapted for, which is convoluted and messy.  Additionally, we must understand both biological and cultural evolution.  The main cultural changes include the Agricultural Revolution and the Industrial Revolution, both of which had profound effects on the environment that humans lived in.  If we gain a better understanding of our adaptations and the effect of cultural evolution, we can gain a better understanding of what is causing mismatch diseases.  Unlike genetic disorders, which are passed on by biological evolution, mismatch diseases are passed on by cultural evolution, where we pass on the same environment and habits to our children, creating a feedback loop.  This feedback loop can only be broken by knowledge of the factors that cause mismatch diseases in the first place.