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No. 2927:
Dual Inheritance Theory

by Krešimir Josić

Today, let's talk about cultural complexity. The University of Houston Mathematics Department presents this program about the machines that make our civilization run, and the people whose ingenuity created them. 

The theory of evolution is well understood and accepted. It explains how simple organisms gave rise to the multitude of complex creatures that inhabit our planet. But human societies and cultures also changed over the ages. The small hunting groups of our ancestors were the precursors of today's complex states, their stone tools replaced with the smart phones in our pockets. Does the evolution of our genes also impact cultural changes? Can cultural shifts impact the genetic makeup of our species in turn? 

A number of examples support this idea. For instance, most ancient humans were lactose intolerant. However, as our ancestors domesticated animals, milk became a readily available food source. Those that could use it had an advantage over those that could not. The ability to digest milk in adulthood thus became widespread in certain societies.

chemical structure of lactose
A figure of the chemical structure of lactose — the molecule which is split by lactase [Wikipedia/NEUROtiker]

A cultural change — the domestication of animals — thus influenced our genes. But this new ability to drink milk in turn affected our culture. Those of our ancestors that could digest milk were less likely to slaughter their cattle for food. Some became shepherds, and developed pastures. Hence, changes in our genes in turn influenced how we spend our time, how we raise animals, and how we use the land. 

These processes are the domain of Dual Inheritance Theory — a mathematically grounded description of how our culture and our physical selves co-evolved. 

The theory also suggests that our capacity for culture evolved along with our genes. How we innovate, and how we propagate knowledge has been shaped by evolution. The cost of experimentation can be high — you don't want to be the first to try a new type of plant or mushroom. If you remember a successful way to hunt, you'll prosper. To use a well-worn phrase — we're lucky that not every generation needs to re-invent the wheel. And since our ability to learn is beneficial, it's possible that good learners had more children, who were good learners in turn. The capacity to learn and impart information may have evolved and shaped our culture. But these capacities may have shaped our genetic selves in turn. 

Indeed, our capacity to absorb cultural information is remarkable compared to our closest relatives. Consider the Kellogg family who in the 1930's began rearing their baby son, Donald, along with a baby chimpanzee. Their goal was to see whether the chimp would learn to behave and vocalize like a human. However, the experiment was halted when baby Donald started copying the chimp's shrieks.


Comparative Tests on a Chimpanzee and Human Infant pt 1, 1931-1932


Comparative Tests on a Chimpanzee and Human Infant pt 2, 1931-1932

We have now mapped the human genome, and found that we are not just a direct product of genetic information. The evolutionary biologist Theodosius Dobzhansky said that "Nothing in biology makes sense except in the light of evolution." To understand humans and our societies we will need more than understand the evolution of our genes. We will need to understand how they evolved along with our culture.

This is Krešo Josić at the University of Houston, where we are interested in the way inventive minds work.

(Theme music)

Here is an interesting article about the evolution of lactose tolerance

A classic book of Dual Inheritance Theory is Culture and the Evolutionary Process by R. Boyd and P. Richerson. One of their conclusions is that humans are less likely to transmit cultural information from parent to offspring, and prefer conformist transmission, i.e. learning from the broader environment.  If conformist transmission is the norm, this may have a profound influence on how our culture develops

This episode first aired on February 7, 2014.