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Dual Inheritance Theory

January 15, 2014

Here is a piece I am writing for Engines.  The problem  is always to make a clear, concise presentation.  This makes it difficult to address any controversies.  Evolutionary theory is not controversial (at least not amongst those who know what they are talking about).  However, Dual Inheritance Theory is far more recent, and it is not fully developed.  Here is the story – comments are welcome, of course:

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?

There are a number of examples to 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.

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 approach to understanding 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 was shaped by evolution. But the cost of experimentation can be high – you do not want to be the first to try a new type of plant or mushroom. If you remember a successful way to hunt you will prosper. To use a well worn phrase – we are lucky that not every generation needs to re-invent the wheel. Our ability to learn is therefore beneficial. It is possible that good learners had more children, who were good learners in turn.  The capacitity to Learn and impart information may have evolved and shaped our culture.  But these capacities may have shaped our genetic selves in turn.

If you compare our abilities to those of our closest relatives, the difference is remarkable.  Consider the Kellogg family who in the 1930’s began rearing their baby son, Donald, along with the baby chimpanzee Gua.  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.

We have now mapped the human genome, and can sequence it for less than $1000.  We now know that we are not just a direct product of this 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.

Some notes:

Here is an interesting article about the evolution of lactose tolerance. Here is a link to Theodosius Dobzhansky’s famous essay “Nothing in Biology Makes Sense Except in the Light of Evolution“.  More about Winthrop Kellogg  who was an interesting character, and his experiment.  I couldn’t find more information about what happened to Gua after the experiment, except that she died a year later.

A classic book of Dual Inheritence Theory is Culture and the Evolutionary Process by R. Boyd and P. Richerson . One of the conclusions is that humans should are less likely to use parent-to-offspring transmission cultural information, and prefer conformist transmission, i.e. learning from the broader environment. Over the last decades it has beceome easy and chap to access a broad range of cultural models. If conformist transmission is the norm, this may have a profound influence on how our culture develops.


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