DNA is often identified with the “birth guide”, while “learning” is recognised as that which defines us later in life. But this is nothing more than a pervasive and persistent error. The reality is much more interesting than that.
DNA is the way that growing up is recorded in our nature. British zoologist and writer Matt Ridley calls it nature via nurture, to nature through nurture, in a solvent paraphrase of the Galtonian dilemma. This is the key to understanding DNA as an object of controversy.
Let’s take cancer, for example. They are not hereditary, but they are all genetic because they appear due to an accumulation of mutations in the DNA of our cells.
Each of our neurons or our liver cells carries a copy of the whole human genome and it is thanks to that it can function properly.
DNA is not only the vehicle of inheritance from parents to children, but also the operating manual of each of our cells throughout our lives.
Cancer treatment is already benefiting from DNA technology, although genomic oncology is only in its infancy.
The leaders of this discipline, like Bert Vogelstein, calculate that most tumors are due to the accumulation of half a dozen key mutations of the thousands that accumulate in any of our cells throughout the life, and in particular the cancerous ones.
These mutations are distinct in each tumor type. In women with breast cancer, for example, it is already common practice to analyze their key genes, because it depends on the optimal treatment, whether modest chemo or a radical breast excision. This strategy is becoming widespread in other types of cancer, even though its results are poor.
So, cancer is nature or parenting? It is both. We have all seen those photos of a family in which three generations of women have died of breast cancer.
In this case, the inheritance is what weighs: the mutations with which those women were born were the cause of their fatal destiny.
A more common case is that some mutation or another comes from birth and that the rest have been acquired during life, sometimes by carcinogenic factors such as tobacco smoke or ultraviolet radiation from sunlight. And at other times – many other times – by mere chance.
This is an important concept worth dedicating a few more lines.
Recent results from large cancer genomics projects show that one-third of the cancers that afflict the world are due to risky living habits such as smoking, burning on the beach or eating more than is strictly advisable in addition to the ingredients present in food products, among others.. But the remaining two-thirds are not the fault of the patient, but a product of chance.
Since the ovum and the sperm become fertilized, our cells divide hundreds, thousands or tens of thousands of times, depending on what type they belong to.
In each of these divisions, the entire genome has to be replicated, made up of 3 billion letters, and however precise the DNA replication system maya be, errors occur that propagate to the next cell generations. Two of every three cancers come from that chance.
But whatever the source of a key mutation – or whoever is to blame for it – few scientists and doctors doubt that its detection is essential to decide the treatment. Unfortunately, most treatments still use techniques and products that enhance cancer growth as supposed to treating the root cause of it.
DNA is nature and parenting or, as Ridley would say, nature by way of parenting. During our lifetime, the environment and mere chance become flesh in the genetic sequence of each of our cells.
Cancer is a good example to illustrate the complex internal harmonies of the “born or done” issue that focuses our debate. But it’s just an example. Brain development and mental illness is a topic closely related to this topic, although it may not seem so.
Fred Gage of the Salk Institute of California has shown in recent years that our brain is a mosaic of neuronal clones with distinct genomes. As in the development of cancer, different areas of our brain have accumulated mutations during cell proliferation from fetal development to adulthood.
There are several types of mutations – the favourite of theorists is the change of a single letter in the genome, but the one that draws the most attention in our brain is of a very different nature.
Half of the human genome is what is called transposons, or moving elements, DNA segments containing some information, copies of itself that are inserted elsewhere in the genome.
Almost all of these transposons are mere genomic fossils, but Gage has discovered one, the LINE 1 that remains active in the genome. It jumps from one place to another as we develop in the uterus and live outside of it, and especially in the cells destined to form our brain.
When LINE 1 changes position in a brain stem cell, all of its descendants inherit the new position, although some of them add another jump to the previous one, and so on.
A transposon like LINE 1 is a DNA text that means “grow and multiply.”
The discoverer of these essential lines of code in evolution was the twentieth century’s most brilliant geneticist, Barbara McClintock, who took 40 years to give her the Nobel Prize for some reason that no one has convincingly explained.
McClintock not only demonstrated that there are elements of DNA that jump through the genome – the reason for which they gave the Nobel – but something much more important, although not for the Swedish Academy: that those jumps from one place of the genome to another were a response to the environment and, therefore, important for the development and evolution of an organism.
This is the kind of perception that transforms science, but only after a couple of centuries. Rome took four to forgive Galileo, so the scientific community is already slow in rehabilitating McClintock’s fundamental ideas. Fear of trolls is not a good science advisor.
Another essential question is epigenetics. Cheap psychologists, cosmetologists and acolytes of modern religions are turning epigenetics into a motto, a slogan or a banner of their prejudices.
For them, epigenetics comes to reveal that genetics is wrong, that in the end is the effect of the environment that counts.
We are born with dozens of talents coded in our DNA. That is why you cannot teach a dog to talk, but you can do so to any human baby. And there are also differences between babies in their ability to learn a language.
It’s the genetic lottery that comes to you at birth, just like being tall or short, handsome or ugly. Given this evidence, there is a common attitude among social scientists. It consists in accepting that genes can affect our physical traits, but not our psychology.
The cerebral cortex, the seat of our mind, is nothing more than a piece of the body. It is formed by the same biological processes as the liver, kidneys or hands.
A hierarchy of active or inactive genes instructs cells to adopt a destiny, a task, a form. Your hand and your foot are made of exactly the same tissues and cell types, but they have a different shape because some key genes perceive their position in the whole and react accordingly.
It is the same in different regions of the brain, and it depends on the particular genetic variants that one carries from birth and also from those which he has developed during growth.
Our basic psychology is written in the genome, sometimes clearly, most of the time through inextricable paths. Paths that only neuroscience can decipher.
In reality, epigenetics means “on top of genes.” They are genetic changes that are not due to true mutations, but to other things that stick to the sequence and make it more or less accessible to systems that read genes.
The two essential things that stick there are proteins called histones and some of the simplest radicals in organic chemistry, such as methyl. Despite not affecting the sequence, these things that stick to it endure several generations, whether of proliferating cells or people in reproduction.
Epigenetics is not the opposite of genetics. It is a level of regulation that allows DNA to respond to the environment. And the proteins that allow it are encoded in the genome, like all the proteins that make up our body and our mind.
This is the essence of DNA as an object of controversy, but not the least of it. Biological evolution is a product of DNA. This time not from the DNA that is in our neurons or in the cells of our skin, but from the one we passed from one generation to another.
It is also in our cells, but only in very infrequent and special ones: the germ line, the cells that generate our eggs and spermatozoa.
There are mutations very similar to those that cause cancer in skin cells or schizophrenia in developing brain tissue. But there, those changes have no effect on the person who suffers them, but on their children, their grandchildren and all their offspring.
This is the raw material of evolution, its genetic and molecular substratum. In the genome of each of us is written the evolutionary history of the species, or rather, of the small part of the species that has survived in the last millions of years, at hard times flooded with famines, droughts and wars. DNA is a window of precision that we have open to understand the past of the species.
DNA is also the great hope we have of fighting rare diseases, those 3,000 hereditary conditions that each affect very few people and therefore have very difficult to attract investment from the pharmaceutical industry, but together they are a heavy load for a substantial fraction of the population.
The hope of gradually finding treatments for each of them is unrealistic. More effective can be to investigate remedies against what these 3,000 ailments have in common: a mistake in DNA that is either carried by inheritance or caused by the environment and the food we eat.
This is predictably one of the most controversial issues of biomedicine in the near future.
With genomic editing techniques such as CRISPR, scientists have at hand a procedure capable of eradicating rare diseases, but also, in the wrong hands, some people have the power to unleash human extinction.
it consists of correcting the responsible mutations in the human embryo, or even in the ovum or sperm that generate it. That will not only eliminate the rare disease in children, but also in all the progeny that generate for the centuries to come.
DNA has put future human evolution within reach of our technique. Like any method, however, it can be used well or badly.
Let us be intelligent, if only for a change.