As I reported the other day, New Scientist has a special issue on evolution (photo below), which apparently consists of their admission that Darwin was right after all, along with a “feature special” described as follows:
Our modern conception of evolution started with Charles Darwin and his idea of natural selection – “survival of the fittest” – to explain why certain individuals thrive while others fail to leave a legacy. Then came genetics to explain the underlying mechanism: changes in organisms caused by random mutations of genes. Now this powerful picture is changing once more, as discoveries in genetics, epigenetics, developmental biology and other fields lend a new complexity and richness to our greatest theory of nature. Find out more in this 12-page feature special.
The article, which you can’t access online—though judicious inquiry will yield you a copy—consists of 13 numbered scientific areas that are supposedly prompting a reboot of modern evolutionary theory. I’m not going to reprise all of them, as I’ve done so already about many of the “buzzwordy” areas, including epigenetics and niche construction, but I will single out, over the next week, several of the areas that are, to my mind, exaggerated or grossly misrepresented. For readers who’ve said that New Scientist isn’t so bad, my response is, “Well, its coverage of evolution, at least, is dreadful if you know things about modern evolutionary biology.”
True, in some of these areas the article pays lip service to the fact that they’re “controversial”, but the impression one gets is that evolutionary biology is teeming not just with new ideas, but with new ideas that are non-Darwinian and promise a dramatic revision of the theory. The problem is that most of these new areas are either mistakenly conceived or don’t constitute much of a change in evolutionary theory. In fact, none of them do more than put a new duckling under the wing of Darwinism, and none of them replace the mother duck.
Today’s target is GENETIC PLASTICITY, the first of the supposedly “new” areas of evolutionary biology. It’s described under the clickbait-y title “Genes Aren’t Destiny.”
My immediate response is that we’ve known about genetic plasticity for over a century. But let’s back up: what is genetic plasticity?
It’s simple: it’s the observation that for many genes, their expression depends on the environments in which the organism that carries them (and hence the genes themselves) develops or experiences. There are a gazillion examples. For some genes, you get a permanent effect depending on the environment obtaining during the organism’s growth. One example, which I and two colleagues used in an experiment on the temperature flies encounter in the wild, is the mutant allele white-blood, which affects eye color. The expression of the mutation is sensitive to temperature during just a narrow window of time when eye color forms in the pupal stage. If the temperature is high, the eye can turn out very light yellow or even white, but if the temperature is lower, the eye is darker, down to dark purple. After this sensitive period, the eye color stays the same for the fly’s life. The color is said to be “plastic with respect to temperature.”
Likewise, if you don’t get enough food as a kid, you’ll be permanently small after puberty. That’s because the genes involved in creating “height” are sensitive to the amount of nutrition the organism gets, making “human height” a plastic trait. There are a gazillion genes that are plastic in related ways; in fact, I know of very few genes whose expression isn’t affected by the environment (perhaps genes for polydactyly in humans and cats are examples of the latter).
Some genes can vary their expression over an organism’s lifetime. Cats get thicker coats in winter and revert to shorter coats in summer: the genes producing hair are reversibly plastic to temperature. Snowshoe hare become white in winter and brown in summer, a reversible case of pigment genes sensitive to temperature.
The fact is that since the advent of Mendlian genetics at the beginning of the 20th century, geneticists have recognized the plasticity of genes and the traits to which they contribute. The terms back then were that genes had “variable expressivity” or “variable penetrance” depending on the environment. (White-blood was described in 1945.) The idea of plasticity is not at all new, and was featured in the founding works of the Modern Evolutionary Synthesis in the 1930s and 1940s. It was an integral part of our modern view of development, which has long recognized that almost no traits are produced as invariant by genes acting independently of the environment, while the expression of most genes and traits involve an interaction between genes and environment.
I give you this primer because New Scientist, in #1 of its litany, pretends this idea and its instantiation in organisms is something new and exciting. In fact, they say, citing the Human Genome Project, that we now realize that this kind of interaction refutes genetic determinism:
The more we learn about genetics, the clearer it becomes that “genetic determinism” – the idea that genes and genes alone fix our destiny – is a myth. A given set of genes has the potential to produce a variety of observable characteristics, known as phenotypes, depending on the environment. An Arctic fox changes its coat colour with the seasons. The presence of predators causes water flea Daphnia longicephala to grow a protective helmet and spines.
The power of flexibility
Even a change in social environment can prompt a shift. In the European paper wasp (Polistes dominula), for example, when the queen dies, the oldest worker transforms herself into a new queen. But she isn’t the only one to respond. Seirian Sumner at University College London and her colleagues found that the death of a colony’s queen results in temporary changes in the expression of genes in all workers, as though they are jostling genetically for succession. This flexibility is key to the survival of the colony and the species, says Sumner.
The power of genetic plasticity can be seen in the humble house finch. In the past 50 years, it has colonised the eastern half of North America, moving into habitats ranging from pine forests near the Canadian border to swampland in the Gulf of Mexico. The finch’s underlying developmental plasticity provided the raw material from which novel features evolved, including a range of new colourings and other physical and behavioural traits, says David Pfennig at the University of North Carolina at Chapel Hill. “Stop thinking about this as being like genes or environment, because it’s a combination of the two,” he says.
That’s all she wrote (the author of this section is Carrie Arnold).
Let us note that some plasticity, like hair growth in mammals during winter and coat color in snowshoe hares, has evolved: the changeability of the genes in new environments is an adaptive phenomenon (creating more warmth with longer hair and better camouflage in winter). Plasticity is not always a given and inherent characteristic of genes and traits, but in many cases has evolved as organisms have experienced different environments during their species’ evolutionary history, making lability an advantage over fixity.
Further, one can construe “genetic determinism” in two ways, which the article conflates. First, one can see it the proportion of variation in one trait in one population of organisms that’s caused by the variation among the genetic endowment of individuals. The proportion of variation among individuals in a population due to variation in their genes is called the heritability of that trait, and ranges from 0% to 100%. In humans, for example, the heritability of height in many populations is about 80%, meaning that about 80% of the variation in human tallness that we see in a given population is due to variation in genes. This does not mean that height itself cannot be affected by the environment, for it clearly can (I used the example of nutrition above). But under the existing conditions in a population, one can construe the heritability as an index of genetic determinism in a given population under existing environments.
But one can also construe genetic determinism as the degree to which the expression of a trait or gene in an individual is affected by the environment. If this is what the article means, and I think it does, yes, plasticity does show that genes are not the be-all and end-all of a trait.
The important thing, though, is what I said above: THIS IS NOT NEW AT ALL!. It is simply either ignorant or mendacious of New Scientist to pretend that genetic plasticity is both a recent discovery and one that has revised neo-Darwinism. Genetic plasticity was recognized well before neo-Darwinism was formulated in the 1930s as a fusion of genetics, natural history, and evolution, because genetic plasticity was known since the very early days of genetics—almost since Mendel’s work was rediscovered in 1900.
So, if you are masochistic enough to read the entire New Scientist article, you can just move along when you get to point 1; nothing to see here. It’s almost as if the authors touted the claim that the idea of natural selection (which really wasn’t widely accepted until the 1920s) is a new and exciting addition to Darwinism.