- Genes – the language of God 0: Preface
- Genes – the language of God 1: Genes as Language
- Genes – the language of God 2: Other popular gene myths and metaphors
- Genes – the language of God 3: Why genes aren’t information
- Genes – the language of God 4: Why genes aren’t a language
- Genes – the language of God 5: God and genes
- Genes – the language of God 6: Theological implications
There are a number of other metaphors used by the media and explainers when communicating about genes. Some of them have an acceptable interpretation, but may mislead; others only mislead. Before we consider the genes-as-information issue (next post), let’s look at some of these:
Genes as the essence of an organism
A while back I was contacted by a philosopher who specialises in metaphysics, which is the study of what ideas are necessary to make sense of the world. He asked me (as a philosopher of biology) whether, if a coat was made of my own DNA, I would become “bigger” than without that coat on. The idea that he seemed to have was that in modern biology, DNA was my “essence”, what made me who and what I am.
This is a fundamental mistake. DNA does contribute to some of my traits, and it may even contribute to how I develop my personality over time. But it is not my “essence”. The reason I quote mark “essence” is that it is a vague and largely meaningless term. In philosophy it means the properties that make some individual thing what it is: humans, for example, were held to be rational animals, which meant that they had an essential nature that was rational, along with the essential natures of animals (sensitivity to the environment, ability to move), along with the essential natures of all living things (ability to eat and grow, ability to reproduce).
But while DNA is implicated in how all organisms (of which we know) develop and mature, it is not their “essence”. DNA in a test tube will slowly denature (lose its structure and breakdown into its components, called monomers). DNA in an organism that lacks the right conditions (egg, maternal environment, atmosphere) will not enable that organism to continue. A newborn animal placed in a hard vacuum will do little apart from drying out. In short, the relationship between genes and the organism and its environment is summed up with the standard mnemonic:
G & E -> O
or, Genes plus Environment gives you the Organism.
What counts as the environment, however, is a complicated issue. Not only does the environment (for genes) include the ecosystem, as well as the maternal resources (egg yolk, placenta), it also includes the cell mechanisms of the fertilised egg as well; this means the mitochondria, the nuclear membrane, transport mechanisms like the actin cytoskeleton, and a host of other thing, not least ribosomes and cell membrane (or wall in plants). As well as this, it also includes the non-genetic structures that are needed to “express” genes – the polymerases and spliceosomes that are used in the process of making proteins. Finally, the environment for genes includes the machinery that replicates the genes themselves when cells divide – helicases and proteins that initiate replication.
Without all this machinery, genes would do nothing much. So, they are not, on their own, the “essence” of the organism.
Genes “for” a trait
The media often uses the phrase “the gene for” this or that trait, such as language, homosexuality, religion, rape, and so on. This is always misleading, and should never be said, by teachers or the media.
For a start, no gene does anything in isolation from other genes, so finding out that a gene like FOXP2 is implicated in the development and evolution of language is like finding out that 3/4 inch bolts are used in bridge building. They are crucial to the integrity of the bridge, but the bridge is a lot more than those bolts.
Second almost every gene has some other role in the body. Non-biologists will often talk about “the” function of a gene or other body part, but in fact parts of organisms, including genes, will always have many different roles in the normal function of an organism, and claims that “the” function is X are usually based upon what happens when a gene goes wrong. Delete or impair that gene, and language won’t develop. These are called “knockout studies”, because geneticists often remove the gene (knock them out of the organism being studied) to see what effects this has on the physiology of the organism.
Rather than saying FOXP2 is a “gene for language” it would be better to say it is a gene “involved in the development and evolution of language”. It takes longer to say, but it is at least accurate.
Genetic reductionism: it’s all about the genes
In 1976, Richard Dawkins published a book entitled The Selfish Gene. In this book, Dawkins argued that modern evolutionary theory considered that it was the gene, not the organism, that evolved. Critics pointed out some difficulties with this view, and today the consensus is that evolution occurs at all levels from genes to colonies or populations. But one outcome of Dawkins’ book was the introduction of what has come to be called genetic reductionism. Most people think this is a bad idea.
To reduce one level of talk about the world to another used to be considered progress in science. For example, we reduced talk about chemistry to physics when we developed quantum mechanics. Now we know that the reason why molecules for in reactions is that the molecules are made of smaller particles which attract each other and have certain energies that are reduced when a reaction takes place (roughly).
Dawkins seemed to be reducing talk about organisms, and their behaviour, to talk about the interests of genes (which were like selfish economists, trying to maximise their return on investment). However, many people objected to this, because it suggested that only genes were the beneficiaries in evolution, and that all that happened in evolution was adaptation by natural selection.
A philosopher once noted that in philosophy, “there’s the bit where you say it, and the bit where you take it back”. Dawkins expanded his view in subsequent books until he did not differ much from other evolutionary thinkers, but he remained convinced that natural selection was the main engine of evolution. Most evolutionary biologists will argue that much that happens to genes in evolution is anything but adaptive, and that much of what is important in evolution is anything but genetic. This leads us to the next metaphor:
Genetic determinism: biology is destiny
One thing genetic reductionism is thought to imply is genetic determinism. Sometimes summarised as “biology is destiny”, this is the idea that everything you do is directly determined by your genes. Dawkins wrote something like this in the Selfish Gene:
Was there to be any end to the gradual improvement in the techniques and artifices used by the replicators to ensure their own continuation in the world? There would be plenty of time for improvement. What weird engines of self-preservation would the millennia bring forth? Four thousand million years on, what was to be the fate of the ancient replicators?
They did not die out, for they are past masters of the survival arts. But do not look for them floating loose in the sea; they gave up that cavalier freedom long ago. Now they swarm in huge colonies, safe inside gigantic lumbering robots, sealed off from the outside world, communicating with it by tortuous indirect routes, manipulating it by remote control.
They are in you and in me; they created us, body and mind; and their preservation is the ultimate rationale for our existence. They have come a long way, those replicators. Now they go by the name of genes, and we are their survival machines.
The implication is that “we” (as bodies) are just what genes “program” us to do and be, and the genes determine our fate.
This idea is much older than genetics. Plato [in The Republic] thought we were all born with gold, iron or bronze souls, and our fates were determined at birth. Likewise, in the middle ages people thought that one’s “blood” determined one’s social rank (as an aristocrat or a peasant).
In the late nineteenth century this became the foundation for “eugenics”, which sought to breed humans the way a farmer breeds cattle or horses. This was then turned to justifying the extermination of millions by the Nazis, who followed the United States and Canada and Australia in its eugenics program.
Genes don’t “hardwire” people to behave in particular ways. Studies of psychopaths show that many of them live perfectly normal and law-abiding lives, because the negative side of their genetic dispositions was never triggered as they grew (see above, genes-as-essence). Just as people with a metabolic genetic disease can develop normally by avoiding the triggers (phenylketonuria can be prevented by avoiding phenylalanines in their food), pathological behavioural traits don’t always cause particular behaviours. But they can bias how a person responds to the environment as they develop.
In short, biology is not destiny, but it is an influence. Genetic conditions do not force behaviours, but they make some behaviours more likely to develop,
Common genes: what we share with chimps and mice (and bananas)
You will often see “similar DNA” numbers like this: Humans share 99.5% of their genes with chimps, 90% with cats, 82% with dogs, 80% with cows, 75% with mice, 60% with flies, and so on, and supposedly 50% with bananas.
While these percentages scale roughly with the amount of time since we shared a last common ancestor with them, the numbers are often wildly varying. Why?
It all hinges upon the notion of “similar”. There are three main kinds and several minor kinds of ways in which the DNA of one species can be similar to another’s.
One is “base pair similarity”. If each species has a gene X with around 10000 base pairs (“letters” A, T, C and G), and 400 differ, then they are (in that gene alone) 96% similar. However, gene X may be “the same” in its place in the genome and functions despite these differences, and so it can be 100% similar between the two species. Then you have the overall structure of the genome, which is arranged in chromosomes.
If each species has the same chromosome structure, then it can be 100% similar even if many genes are different between the species. But differences can arise when multiple copies of genes are made between species. If Gene X has three copies in species A but only one copy in species B, that can change the “similarity” measure.
Finally, chromosomes can be duplicated even in one species (this is called polyploidy): a species can have 1, 2, 3 or more copies of each chromosome. Obviously whether these count as differences or not depends on whether you are counting the genes, the base pairs, or the chromosome numbers.
So take care. A banana can have a whole host of genes that humans and other eukaryotes (roughly, plants, animals and fungi) have because they are basic genes for organisms to survive. But it will be very unlikely to have the same genes at a finer level of detail (base pair sequence, position, chromosomal arrangement).