Nature and Nurture

The Agile Gene: How Nature Turns on Nurture, published in 2003 by Matt Ridley

Ten years after its publication, this book has aged extremely well. Its incisive views of nature vs. nurture, free will, and emotions have opened new paths for exploration.

Matt Ridley tells beautiful, captivating stories, which are no less true for being so enjoyable. In the first seven chapters of this book he tells stories to illustrate a single point in the ongoing philosophical war of nature versus nurture:

Nature vs. nurture misses the point. It is not nature vs. nurture, it is nature and nurture.

The choice is not binary, it is “both and.” But, as Ridley repeatedly demonstrates, it is even more beautiful than simply “both-and” because “both-and” invites a person to set a dial at 70/30 for the relative contributions, and even to search for a prime mover, the one that started the chain of events. Both of these approaches are simply sophisticated attempts to reduce “both-and” back to the primacy of one over the other.

Ridley proposes a much more complex and sophisticated process, which he calls circular causality, an intimate, ongoing dance between nature (genes) and nurture (environment) in which the lead constantly alternates between the two. A linear view of this process, with time on the x-axis, might look like a game of leapfrog played by nature and nurture, with each responding to the other. But you cannot find a starting point or a prime mover. It is “turtles all the way down.” This, then, is the second and perhaps primary point of this book:

Nature and nurture work together in an elegant dance of circular causality, with no beginning or end.

In the first eight chapters, the author tells stories of experiments, progress, and contention in the areas of genetics, biology, sociology, and sociobiology. Each story is a little treasure, and Ridley weaves them into a rich tapestry of the battle for primacy between nature and nurture. One story will give a good flavor of the competition.

Most people are familiar with duck imprinting, when, in the first three days after hatching, a duckling will imprint on the first moving animal it sees as its mother. This imprinting is done only once, and cannot be controlled or changed by the duck. Imprinting is forever and appears to be a clear victory for nature (the genes responsible for imprinting) over nurture. But wait, says Ridley. Is this such a clear victory for the genes? The genes only determine the time window and permanence of imprinting. What determines which animal the duckling sees first? Why nature, of course. You may respond that of course, the duckling sees its mother first. But some birds, such as the cowbird and cuckoo, never see their mothers, and many reptile mothers abandon their eggs shortly after laying them. So imprinting only works in species where the mother raises the chicks or nurtures them. So isn’t this a clear win for nurture?

But there is a small flaw in the imprinting strategy. Almost always, the duck sees its mother first, but some ducklings might first see a graduate sociology student doing an experiment. In that case, the grad student is now followed by a squawking duckling as she strolls across the university quad. In one duck species, Muscovy ducks, nature (the genes) noticed this flaw and designed a patch to fix it. Muscovy ducklings require two proofs of motherhood for imprinting. The duckling imprints on the first moving animal it sees, but only if she quacks like a Muscovy duck.

How does a duckling know what a Muscovy quack sounds like? It could be hardwired, but nature took a different approach, possibly because there may be significant differences in the quacks of Muscovy duck mothers. A hardwired quack pattern might not be specific enough. The duckling wants to imprint on her own mother, not just any Muscovy duck wandering by.

How can the duckling embryo inside the egg hear a sample quack from its own mother? Muscovy duck embryos quack inside the egg as they near hatching. Wondering if this quacking was the source of the quack pattern to match, an enterprising experimenter cut the vocal cords of a duckling still inside the egg. An amazing technical accomplishment, not to mention a creative approach to answering the question. Sure enough, the duckling with clipped vocal cords imprinted on the experimenter, since the quack pattern to match was simply silence. Is this a case of nature victoriously winning over nurture with a clever second proof of motherhood, or is it more a victory for nuture, which provided the sample quack in the egg?

This story also illustrates the circular causality that Ridley describes. Nature and nurture each respond to the other in a chain of circular causality, or a constant game of leapfrog.

What are Genes?

Ridley introduces his second theme only in chapter 9, “The Seven Meanings of Genes.” As he often does in other books, Ridley saves a bombshell revelation for late in the book. In this chapter, Ridley reviews the discovery of genetics and the development of genetic theory and presents a definition of genes according to several significant discoveries

A unit of heredity, an archive for the storage of evolutionary information. Gregor Mendel, a Russian monk, studied the inheritance of certain traits in peas in the 1860s. He discovered the genetic laws of inheritance and even identified and named recessive and dominant inheritance patterns. His work was lost for 20 years or so, and eventually rediscovered by Hugo De Vries, who published it as his own work in 1990.

An interchangeable part. DeVries did describe genes as interchangeable parts. For instance, the genes that control the body plan for the fruit fly have precise counterparts in the human genome. Both appear to have a common ancestor in the roundish flatworm that lived 600 million years ago. In addition, humans and fruit flies use the same genes for learning and memory.

Health preserver. Faulty genes can cause, or at least allow certain diseases or maladies. In 1902 Archibald Garrod linked maladies to certain genetic traits. To this day many genes, such as BRCA1 and BRCA2, are named for the maladies they cause or allow when the gene is faulty.

A recipe, or what it does. Each gene constructs proteins. The gene can be seen as the recipe and RNA is the chef who cooks up a protein according to the recipe. The protein does the work in the body, DNA holds the master copy of the recipe (the gene), and RNA is the link between them, the chef.

A switch, or a unit of development. Genes switch certain activities on and off. The Muscovy duckling has a very narrow window for imprinting a mother, only 2-3 days after hatching. In primates, the HOX gene controls how long things grow, such as spines, necks, fingers, and toes. Genes can switch other genes on and off in very complicated sequences.

A reproducer. A gene wants to reproduce, The now universal anthropomorphic description of the “selfish gene,” coined by Richard Dawkins, describes a gene as wanting to reproduce itself. “A body is a gene’s way of reproducing itself.” Genes care about their own survival. They do not care about the survival of any specific specimen of the species, only that it reproduces, passing the genes on to the next generation.

A unit of instinct. What is instinct? Ridley suggests that successful genes carry the instinct to reproduce. Evolution is not about survival of the fittest, it is about the reproduction of the fittest.

A device for extracting information from the environment—all of the above. Ridley credits this definition to John Toomy and Leda Cosmides, who pioneered evolutionary psychology in the late 1980s and published The Adapted Mind: Evolutionary psychology and the generation of culture in 1992.

The “selfish genes” have become extremely good at extracting information for survival in the environment because their survival depends on this ability. But the environment is not static, as Richard Dawkins describes in his book, The Extended Phenotype. Dawkins describes how beavers have designed their environment to fit themselves, literally an extension of their genetic code. In the same way, the beehive is an extension of the genetics of bees, as is the nest of the dove, the web of the spider, and the tools of humans. Our genes drive us to change our environment to survive and reproduce even more and better. In circular causality, nature (the selfish genes) responds to changes in nurture (the environment of language, friendships, and families) even as they cause changes in nature.

Free Will

The author takes an interesting excursion into free will vs. determinism, Based on recent experiments, he proposes that free will is real and resides in the limbic system, not in the conscious brain. The limbic system is an old structure found in all mammals and even in reptiles, birds, and amphibians. The limbic system controls survival behaviors, emotions, and temporary levels of certain chemicals in the body, such as testosterone and adrenalin.

The limbic system controls essential behaviors for life, such as getting food, self-preservation, and reproduction. Note that reproduction is not strictly necessary for the survival of the individual, only for the survival of the genes. Since the purpose of the individual, at least from the viewpoint of the selfish genes, is reproduction, the genes hardwired reproduction into the survival behaviors of the individuals.

In fact, the limbic system controls most of the body, except for direct sensors like the eyes, ears, and nose. Muscle control goes through the limbic system. The conscious mind may create the email message, but it does not know and cannot directly control the details of how a finger types a letter on a keyboard. Like an executive, it simply tells the limbic system to type the letter ”e.” The limbic system controls which muscles contract in what sequence and force to strike the key.

Self-preservation, often called “fight or flight,” usually needs a fast response and high energy. The limbic system can inject chemicals, such as testosterone and adrenalin, into the body to help it fight harder and fly faster. The limbic system increases the heart rate and breathing rate to get more oxygen to the muscles for better fight and flight.

The limbic system also controls emotions because they serve as rewards or motivators for survival behaviors. Hunger motivates a search for food, just as contentment serves as a reward for a good meal. Fear and anger serve as motivators for fight and flight.

Pain is a powerful motivator. When you touch a hot stove, your hand jerks back before the pain/heat signal even reaches your conscious brain. When the limbic system receives a pain/heat signal from the nervous system, it senses a self-preservation need and responds immediately, telling the muscles to jerk back. Only a little later does it send the pain/heat message up to the conscious brain, which can take up to a half second to process the message.

Conscious Brain vs. Limbic System? Left Us Hanging

Ridley opens the box of free will by locating it in the limbic system but does not pursue several tantalizing questions about locating free will in the limbic system. How does the conscious brain communicate with and coordinate with the limbic system? If the limbic system controls emotions, how does the conscious brain deal with emotions? If the limbic system is the source of free will, how exactly does it “choose” what to do?

Are these emotions present in the limbic systems of other mammals, or even other animals such as reptiles and birds that lack a forebrain? Primates exhibit emotions. Do they have free will? What about cats, dogs, and mice?

Culture, Memes, and Evolution Beyond the Genes?

In a similar manner, Ridley argues persuasively that culture (in a broad sense) is a significant determinant of the environment for humans, going back to hunter-gatherer tribes using fire and flint. But culture, even a broad definition, has accelerated considerably since the stone age. Genes evolve over hundreds or thousands of generations to respond to environmental changes. Of course, some changes can occur much faster. A particular species of moth in London had dark wings to blend in with the soot that covered everything in the industrial age. As the air in London cleared when coal burning ceased, the moth’s wings swiftly switched to a light color. With a generation cycle of a year, moths can respond faster than humans, and birds provided a powerful incentive by eating all the dark moths.

Can genes evolve in response to rapid, complex environmental changes such as cars, electricity, internet, and dietary changes due to processed food? Have genes become obsolete? Will further evolution move from the physical space into the digital or mental space of “culture” with memes?

Others have written on these topics. I sincerely hope they are on Ridley’s list of future topics for books.