Manuel Ruiz Torres
Introduction. Some basic concepts
One foundational paradigm in biology is the genetic code existence, it (genetic code) allows to transcript the molecular structure and composition of proteins that shape cells, tissues and organisms, and enable thousands of biochemical reactions necessary for life.
Figure 1. Scheme of the basic structure of the DNA in the chromosomes.
The genetic code is based on genes, which are fragments of deoxyribonucleic acid (Figure 1), -or DNA, as it is commonly known by its acronym in English-, that are transmitted from one cell division to another, and from one individual to the next generation ,ensuring the code needed to make proteins is not lost.
DNA encoding system is very effective. In a brief explanation, DNA macromolecules contain a very long series of smaller units, called nucleotides (Figure 2), (of which there are four adenoidal, A, thymine, T, cytosine C, and guanine, G). The sequence of three nucleotides, called codon or triplet, codes the election/choice of an amino acid. Amino acids are small molecules that build gigantic proteins. There are 22 amino acids required to make proteins.
Figure 2. Nucleotides that form a part of the nucleic acids.
Each tRNA has two parts which interest us, one which binds/unites with the mRNA and which is specific to each triplet, and one opposite which is attached to an amino acid, which is always the same, so each specific sequence of three nucleotides corresponds to an amino acid (Figure 3). For example, if to the triplet CAA (cytosine nucleotide followed by two adenosine) is added a specific tRNA, which in one end of it carries the amino acid glut amine. If after CAA its positioned CGC, to this a tRNA that carries at its end the amino acid alanine positions, and its placed adjacent to the glut amine, they will establish links, and so on. Thus, a sequence of 1000 triplets results in the construction of a protein chain of 1000 amino acids.
For sure ,in the genome, DNA molecules set of cells, are contained the keys to make all existing proteins
Figure 3. Scheme that shows the manufacture of the proteinsProcess, very briefly, is as follows. From the DNA chain, consisting of thousands of thousands of nucleotides, its made a reverse copy (as a mold) that is the Ribonucleic messenger acid or mRNA (mRNA). On the mRNA molecule, other molecules known as ARNt (Ribonucleic Transfer acid) begin to position themselves but in a special order.
existing in cells, encoded by the genetic code, a set of rules to assign a sequence of nucleotides of the DNA, an amino acid sequence of a particular protein. Since proteins are essential for life (both in the construction of structures such as the catalysis of biochemical reactions), soon it reached the idea that genes, through the genetic code, control and regulate the biological functions and the development of the organism itself.
A matter of culture or genetics?
In 1976 Richard Dawkins published The Selfish Gene, in which he develops the idea that evolution is completely blind, and relies on genes. All life circumstances serve to preserve and transmit the genome. Dawkins is not a geneticist, but zoologist, but a strong Neo-Darwinism advocate, and his book does not leave anyone indifferent, praised by those who see natural selection as the only engine of evolution and the pillar of existence, and criticized by those who do not accept that genetics is behind all human actions.
From Adkins’s work, its emphasized the idea that genes are responsible for everything that happens to the individual, including humans beings. A genetic response is seeked for everything: character traits, diseases, form aspects, social behavior, even culture elements. It was (and is) very common to develop research programs in which the search for the genetic explanation is what matters. However, it has traditionally been a strong rejection from the human sciences ( anthropology, sociology, psychology,) to consider that aspects of the human being, more genuinely human, as behavior, or the development of a society or a culture, are the result of the action of genes. Even from the field of political thinkers, thinkers related to the left wing have been very reluctant to admit these supposed implications of genetics in the subtlest of human being.
In this matters, against the Genetic Determinism line of thought, the majority line of thought (besides out of many biological researches) in the twentieth century has been that the main element responsible for the distinctly human traits (culture and society) are found in the environment, not genes. The human being will born as a blank page,and in the course of life, especially the early years, would acquire the personality modulated by the environment itself.
The idea that there are few innate elements of personality, and that this is is modeled from within the family and social environment, was formulated by the philosopher John Locke in the seventeenth century, and later educational ideals of the Enlightenment embraced and promoted. Later, Marxism is also based on this idea of society as a determinant of human development. Sigmund Freud continues to provide important arguments to this effect, when he says that childhood experiences determine the individual the rest of his life. In the field of anthropology, Franz Boas urges cultural ism as a school which advocates that the traditions and culture may influence human behavior in many directions. And BF Skinner carried behaviorism, and affirms that the
human being can be conditioned by any external stimulus, with the right training (similar to Pavlov’s dogs.) So, mean while biology stated to be gathering evidences of a certain genetic
determinism , the human sciences and some relevant biologists go rushing along to UN link, through all the twentieth century , the development of culture and human behavior from the power of genes. Thus, for example, Leda Cosmides and John Toody shaped what become known as the standard model of social science of human behavior, in which they assert that human nature can take any type of settings based on appropriate cultural conditioning . Another example in the line to deny genetic determinism, the edition of the book It is not in the genes: racism, genetics and Ideology in 1984, biologists Lewontin, Rose and Kamin, which accuse colleagues, Wilson and Dawkins , to promote a rough determinism that legitimizes social disadvantage. At the other end, the biologist EO Wilson developed in the seventies the concept of sociobiology, on the discoveries in the behavior of many species. Goes on to suggest that human nature (understood as behavior) as well as other animals, had a biologicalbasis that could be pursued. But long before, a form of genetic determinism, eugenics (“good breeding”), began to develop in the late nineteenth century, based on Darwinism. The idea was to promote the improvement of the human race favoring certain unions, which supposedly would result in individuals with better attitudes . But soon,
eugenics led to government programs to prevent marriage or reproduction of individuals “dumb or mentally weak feeble minded” which was practiced in many Western countries and many U.S. states. It was not until the seventies that eugenic practices wereconsidered illegal. Until then tens of thousands of individuals were sterilized, and an even bigger number of marriages were banned.
The Human Genome Project
Figure 4. Set of chromosomes of the human being.
Intending to know “the language in which God created life”, President Bill Clinton in 1990 launched the international Human Genome Project, funded by various governments and charities, and directed by James Watson (co-discoverer of the molecular structure of DNA). The goal was to read the 3 billion base pairs that contain the genetic code of humanity (Figure 4).
In 1998, when he had broken the 3% of the code, the researcher Craig Venter started another project to read the genome, with a methodology faster and the financing of Celera Genomics. A race began which consequences could be very different depending on which project will meet the target, because although Watson team wanted the knowledge of reading genome was available to all, Celera Genomics is looking business and patent. Coincidentally, both teams finished about the same time in 2000, so it is considered a tie, and President Bill Clinton promoted an agreement between both sides, until finally, in 2004 all the results, the genome deciphered in full, were deposited in a database accessible to the public, called GenBank, and it was felt that this
information was the patrimony of humanity.
But after all, the genome revealed a few surprises, which forced to correct some basics of genetics. First, the number of genes.
Figure 5. The worm Caenorhabditis elegans has a number of genes lightly lower than the human. The number of genes does not correspond with the degree of complexity of the species.
As it is recognized in humans more than 100,000 different proteins, according to the by then axiom “one gene, one protein”, it was expected to find at least 150,000 genes. Some spoke of up to 300,000 genes. However, in the end only 21,500 were discovered, a figure lower than the genes of a mouse and only slightly higher than those of a small microscopic worm (Figure 5) whose body does not reach thousand cells, so the complexity of the organism does not match the number of genes. If each gene contains the possibility of hundreds or thousands of different proteins, it means that the factors that regulate the decoding is more complex than previously suspected.
Figure 6 . The consumption of marijuana in the adolescence (external stimulus) influences the activation of a variant of the gene COMT, which increases the risk of suffering schizophrenia, according to the study in the population of Dunedin.
Another surprise was the “junk DNA”, one who has no capacity to encode proteins , comes around the 97-98 percent of the genome. Recently it was discovered that this significant amount of genetic material, rather than being useless, plays an important role in decoding genes. In addition, we have 99% of genome in common with the chimpanzee and 97.5% with the mouse, indicating that large differences between species are based on very few differences in the genome, which makes the other pillar of differentiation, ontogenetic development (the training process from fertilization of the ovum to the individual born) and the factors governing it, acquire a great relevance in evolution.
Is it possible to address with rigor the genetic determinism? As genetic research progresses, it should not be admitted that all the possibilities of human development are conditioned or planned in the genome. At present it is starting to consider that DNA is as a place for storing building plans of all cell proteins. Genes are not read, not expressed, not decoded automatically, there are internal and external factors to the cell that determine that decoding. It can happen that a person carrying a gene whose expression would lead to a pathology, needs certain environmental conditions for its expression, or that certain environmental conditions prevent its expression. This
circumstance completely dismantles inexorable genetic determinism, because the expression of a gene depends not only on its existence, but also it has to set its decoding on, on function of other factors beyond himself.
The Dunedin cohort
The discourse based on “nature and culture”, in relation to the cause of human characteristics (especially those relating to the psyche) are of a genetic or sociocultural nature, which has dominated the twentieth century, was beaten up by the research conducted by Avshalom Caspi and Terrie Moffitt with a large group of people born in 1972 and 1973 in Dunedin New Zealand population. In 2002, these researchers recorded the details of the life experiences of the target population, and an evaluation of their DNA. The results were surprising.
In their research, Caspi and Moffitt studied a gene called MAOA, which has two variants. Children with one of these variants are more likely to have an antisocial and violent behavior, but only if they were also abused as children. Implying, that to have a greater chance of developing a model of antisocial behavior these these two circumstances should be present: having a specific MAOA gene variant and suffer child abuse. The genetic variant alone does not determine anything, but it needed to be activated by specific environmental circumstances. Found another example of this necessary confluence of environment and genetics in the 5HTT gene, which produces the serotonin transporter molecule (neurotransmitter of the brain related to depression, among other functions). This gene has two variations, and Moffitt and Caspi found that people with one of the variants had a 2.5 times greater chance of suffering from clinical depression than people with the
other variant, but only if you also attend specific circumstances (such as loss of employment , divorce, separation from a loved one). When environments are happy, these people show no predisposition to clinical depression. Moffitt and Caspi also noted that a variant of a gene called COMT may increase the risk of schizophrenia if its carriers also smoke weed in adolescence (Figure 6), and that individuals with certain genetic profile have a higher average IQ than average if they were also breastfeeded during lactation. However, people who lack this geneticprofile does not have a negative impact on their intelligence. This comprehensive research led to the consideration that genes and environment, nature and culture, work together in the development of personality. Nature acts through culture and vice versa.
Environment is critical. Epigenetics
The decisive environment´s influence triggering or not of genes has led to the description of a phenomenon called epigenetics, it consists in the genome being able to “remember” environmental influences to which it has been exposed. Generally these epigenetic effects acts on the somatic cells of the adult body (these cells are all the body except those that give rise to reproductive cells, eggs or sperm), deactivating or activating genes. However, sometimes these environmental effects also take place in the egg and sperm,these modulated genes by the environment are transmitted to the next generation. The Acquired characteristics can be inherited (which is totally contrary to the axioms of the synthetic theory of evolution or Neo Darwinism).
Epigenetic phenomena are different from mutations. In these last ones there is a change in the actual sequence of the DNA, but in epigenetic alterations what happens is modifications in the decoding process of genes, activating or not its expression.
A classic Epigenetic example was the study Marcus Pembrey made in 2002 on food availability and life expectancy, using meticulous historical records of crops, births and deaths of the Swedish city of Överkalix. Pembrey found that when children were raised in times of plenty, their grandchildren were more likely to die at an early age. This fact picked predisposition to diabetes and heart disease that occurred in times of abundance, and that was transmitted from father line.
Something similar happened with the Dutch population that was punishedthrough tremendous famine during the Nazi occupation. Pregnant women during the famine gave birth to children with a high risk of health problems arising from these precarious environmental conditions. But this willingness to suffer the same problems remained even among the grandchildren of these women, who suffered no food shortage problem.
In 2008 Mo she Szyf DNA studied the brains of 13 male suicides, and noted that the genetic sequences had not changed, but the epigenetic programming (how genes had gone on and off ) were different from those found in the brains of men who had died of other causes. In other words, environmental effects had conditioned their behavior. In the case of the suicides studied, all had been abused as a child, which triggered this epigenetic change.
Epigenetic processes are essential for normal growth and development. Throughout the life of the organism is necessary to silence some genes and activate other ones. For example, genes that are behind the rapid cell divisions of the embryo, must be silenced by epigenetic processes in the adult organism. When longer be silenced, can lead to manifestation of cancer. These are epigenetic processes that modulate gene expression in a cell that forms part of heart or liver. And this is the influence of the environment.
According to this phenomenon, culture can guide the nature in the expression of genes in response to environmental factors. There have been numerous experiments with mice and other animals cloned (ie, with the same genome), in making alterations in diet, epigenetic effects. Other experiments achieved in mice did not express tumorcausing genes by some dietary additives.
Epigenetic and genetic determinism
But the cultural effects on gene expression through epigenetic phenomena have been observed not only with animal experiments. In humans there is much evidence pointing in this direction. For example, as in other living beings, we have two basic programs for survival: protection and growth. These different types of response are adapted to different situations of aggression or stimulus, and cover a multitude of possibilities and combinations.
In humans, there are two protective systems: one is the HPA axis (hypothalamipituitary- adrenal gland) and the other is the immune system. When a signal triggers
these systems, mobilizing a very complex system that puts the whole body under alert/protection status, with high consumption of resources and growth stop. In all living things, both responses are antagonistic’s. The ability to implement protective response depends not only on external stimulus that denote danger, but also the feeling of fear, anxiety or stress, and in these cases with dire consequences, because a real situation of danger that triggers the protective response is usually punctual. But a state of fear or stress can be maintained over time, so that the protective response remains active indefinitely, causing a large and growth failure influence on all cells of the body Through the cellular environment. Through epigenetic phenomena both protection and growth programs are permanently activated, directly influence the decoding of the genes. And as it has been shown, under certain circumstances this effect on gene expression can be passed to the next generation.
There are numerous examples of how the body’s health is directly affected by epigenetic phenomena launched a continuing situation of stress, anxiety, or fear. Perhaps the most striking, are related to the development of various cancers because they are reactivated genes related to cell division, needed in the fetal or infant stage, but necessarily “off” in the adult. To say that fear kills is no longer a figurative expression to become a very real statement. But we could also say, as a contrary, that confidence gives health.
It has also has been described the importance of epigenetics, the environment, in the prenatal development (Figure 7). In this environment not only affects the power of the mother but essentially the same situations that produce protective or growth responses. It has been studied how mothers and fathers with levels of fear, stress or anxiety high enough to cause the protective response, the same response occurs in the fetus, which slows the growth and development in a crucial phase . It has been shown
how many propensities adult diseases have their origin in these situations.
Figure 7. There are studies that could have traced the effects of certain toxic substances, not only from mother to son, but even up to the following generation of grandsons, due to epigenetics phenomena.
IT has been discovered how there is a real adaptation to transmit acquired characteristics by the mother to the baby via non-genetic ways, as a mechanism for the fetus to optimize its development to adapt to the expected environment. It has been investigated the importance of the aptitude of the prospective parents in the formation of the fetus, even in the months before conception. There are many studies that find relationships between the degree of development of a child and being or unwanted. The events of the lives of the parents influence the mind and body of the child, because in the final stages of maturation of the ovum and sperm, its adjusted the activity of groups of specific genes that will shape the child. It also influences affection, contact, etc. Much of the finish ending depends on epigenetic factors, not the tyranny of the genes.
Given the current genetics level of know ledges (which are continuously expanding with new discoveries) is not without logic to perform the following relationship:
•Through epigenetics the cellular environment (which is a reflection of the environment) could modify the expression of genes, not only in somatic cells (affecting the development of the individual) but also in the reproductive cells (transmitting this change in gene expression to the next generation .)
•One of the aspects of the cellular environment that can generate these epigenetic phenomena is the general mood of the individual.
•The mood can be handled through the mind by numerous tools (techniques of concentration and meditation, imagination, etc.) .
•then through mental processes it can be incised into the genetic decoding and even this determination of gene expression could be transmitted to the next generation.
At this point, mention genetic determinism, relating the development of the human being as determined by the genome, it s going against scientific evidence. Another matter is this to be acknowledge.
