The human gene pool is the source of diversity between us. It is this that attributes to the 0. 1% difference in DNA between you and the next person (Cohen, 2001). Competition, starvation, predators and disease among others acted as selective pressures on our ancestors and thereby pushed and pulled the gene pool in different directions. Overall, those with genes that suited the environment survived and reproduced, while those with less suited genetic make-ups tended to die out without reproducing. However as we advanced through the ages our ability to influence these selective pressures increased.
Starvation was combated through agricultural advances, predators were overcome with the development of weapons, and the age of science led to medicine. With medicine came the ability to essentially keep alive those whom would not have been able to survive in the ‘wild’, so to speak. Some would argue that this culture and technology signalled the end for natural selection as we know it for the human race, as in prolonging the life span (and hence giving the ability to reproduce) to those that would not normally be able to we are not allowing natural selection to take it’s course.
There are a lot more factors to consider though in this debate, if we can determine that medicine does affect the human gene pool, then why is this important? If it can be considered to affect the human gene pool in a negative way, then would it be ethical to use medicine in a selective way to go about rectifying this problem? It is these issues and more that I will be contemplating during this essay. So firstly why is the human gene pool important anyway? It is important to have a wide range of genetic diversity in any population of a species.
One of the reasons why incestual relationships are so taboo is due o the fact that most people have several severely deleterious recessive alleles in their genome, and that these are also likely to be found among close relatives. Offspring from these couples would have a realistic chance of accumulating two of these recessive alleles and hence phenotypically exhibiting these conditions. In reducing the number of genes in the human gene pool, we increase the chances of offspring having these fitness reducing conditions.
Also having a diverse gene pool is thought to be important in case a new selection pressure occurs on a species. With a arge and varied range of alleles in the population then the chances of a combination occurring that aids the organism in surviving better under these new conditions are far greater than if the gene pool was depleted. So let us proceed to the focal point of this essay, the effects that medicine has on the human gene pool, and whether these effects can be considered to be a threat to the gene pool, whether that threat be in terms of diversity or any other factor.
There are probably two general views on the direction in which medicine is heading. The first is that medicine has already bolished the main causes of ill health and that its ultimate aim is to put itself out of business, so to speak. The other extreme to this is that far from withering away, medicine will become more intrusive and demanding, as it preserves the weak and the defective (Medawar, 1965). To coin a phrase from George Orwell, “The World will become a hospital, and even the best of us will only be ambulatory patients in it.
The problem lies with what I have crudely mentioned as preservation of the weak and the defective, the unfit. With any strong hereditary, genetic, inborn human ailment, reserving those who are ill also means to preserve the genetic factors that led to the condition they suffer from. It is whilst bearing this in mind that we shall look at how medicine affects the human gene pool. As mentioned earlier the function of natural selection has been affected by our medical science, which has kept alive, and breeding those whom would normally die from their afflictions.
Perhaps one of the best examples of this is haemophilia. Haemophilia is a disorder of the blood, due to a missing clotting agent the blood could not coagulate and subsequently sufferers were prone to extensive and dangerous bleeding. In he time before the missing clotting factor VIII could be produced artificially and given to sufferers of this disease, death at a relatively early age was common.
These deaths were often a result of bleeds or haemorrhages that simply could not be stopped. As a result the natural tendency would be for carriers of this disorder to die out before reproducing, hence decreasing the frequency of this recessive deleterious allele in the gene pool over time (Giangrande, 1997). However the development of these coagulating factors meant that sufferers could lead relatively normal lives with treatments every so often to aid the clotting f their blood.
With these longer life spans came the chance to reproduce, and hence the gene for haemophilia would not decrease in frequency as would if natural selection were allowed to take place, and haemophilia is still a real and prevalent disorder in the world today. This theory can be applied to a wide variety of genetic disorders that are present in the human population further examples are conditions such as phenylketonuria or galactosemia. Another function of medical science is to allow those to reproduce who would not be able to naturally, in the form of in vitro fertilisation (IVF).
This involves the joining of a sperm and egg outside the woman’s body (in vitro means in glass i. e. test tube) and when fertilised this embryo is then implanted into the uterus where development takes place as normal. I believe that this side of modern medicine exhibits both sides in the context of ‘threatening’ the human gene pool. IVF is used for a number of reasons, some of these such as low fertility in men or missing sections of the female reproductive system.
Some of these can be linked to genetic defects at birth, and hence could be passed on to future offspring. This follows the same trend of conserving genetic disorders in he gene pool as was examined in the context of disease previously. However IVF can be used for couples that cannot have children for some other reason than a genetically predisposed condition. Whether this is due to a problem in later life in the woman’s reproductive system, such as a blocked fallopian tube, or perhaps paralysis that prevents sexual intercourse.
Although in terms of natural selection these couples would not have offspring ‘in the wild’ they could have perfectly diverse and genetic disorder free genomes that would contribute to diversity in the human gene pool if they were allowed to reproduce. In this context then perhaps modern medicine could be considered as a help not a hindrance to the human gene pool, in allowing diversity in situations where it would not arise naturally. Let us now consider the human gene pool as a source of fitness, that is, a smaller gene pool would result in a smaller number of genes and hence generally a population’s fitness would be reduced.
We have looked at the way in which medicine enables defective genes to remain in the gene pool which could lead to a loss of qualities that confer fitness. However we could argue that medicine will simply mean the loss of genetic devices that onfer fitness in bad environments, and that this would lead on the whole to genetic improvements. There is a good case for saying that improvement of the environment improves mankind genetically and that it is better not to have an inborn resistance to many particular hazards and stresses if they are no longer present. Take the example of malaria resistance, via the sickle cell trait.
Sickle cell anaemia results from a faulty gene which causes the red blood cells to become bowed or sickle shaped instead of concave, as they are in a healthy person, as a result of abnormal haemoglobin forming. This condition is exhibited in its fullest and harshest form if two of the recessive alleles of this gene are found in the genome. Sufferers rarely survive past their mid twenties. However having just one of these alleles and one normal haemoglobin allele confers a great advantage in areas where malaria is found in high incidence because this genotype confers resistance to the disease.
As a result the tendency for the sickle cell gene to remain in the gene pool is high in areas such as Africa where malaria is prevalent, as it is often only the people who are carriers of the sickle cell allele that survive to reproduce, due to their alaria resistance. These genetic devices serve a purpose, and a crucial one in areas where malaria is still rife. However we must consider what happens if, due to medicine or some other environmental factor, the occurrence of malaria decreases to a point where it is no longer a realistic threat to the members of the population.
This sickle cell trait would be useless, in fact it would be actively harmful, as it does cause the carriers to have some sickle cells, these are just complemented by the presence of normal blood cells that are found when the double recessive genotype (sickle cell anaemia) occurs. It would be beneficial in a malaria free environment to not have any sickle cell alleles as all of the red blood cells would be functional. In this case we can clearly see how improvement of the environment, through measures such as medicine, would lead to a genetic improvement.
It would result in this gene being selected against and so its frequency would decrease in the gene pool. This is a good counter argument to the point that medicine’s main vice is to allow those whom have genetic disorders reproduce (Giangrande, 1997). Whilst considering the advantages and disadvantages that medicine may ave on the human gene pool we did not really bring the subject of ethics into the frame. Although not directly linked to the objective of this essay it is very important in an area that can easily be incorporated into eugenics.
The real question to be asked if it were to be found that medicine was doing harm to the human gene pool, and hence threatening the fitness of the human race, then would it be right to do something about it? In order for this to happen then extreme measures would need to be taken. This could be in several forms, genetic engineering of embryos to alter enomes to remove genetic defects, or as crude as stopping treatment of those with genetic disorders to prevent these genes being carried forward into the gene pool (Medawar, 1965).
Obviously the last point was completely unfeasible, it would be inhumane not to work towards and subsequently treat the diseases that genetic disorders are responsible for. Perhaps the only way to work around this would be genetic testing of couples before they decide to have a child, in this way at least they could be made aware of the risks from genetic disorders if there are anyway. If this were the case nd the chances of passing on a genetic defect were high then the parents could be discouraged from having offspring.
All in all this is one of the greatest ‘minefields’ in science today, these boundaries on what is acceptable science and what becomes ethically unviable are hard to draw, and differ from one person to the next. I have seen through the topics raised in this essay that there is a well found fear of building up a genetic liability in the human gene pool due to modern technological advances such as medicine. It would be hard to argue that medicine does not place pressure upon the diversity and strength f the human gene pool (Hartl and Jones, 2001).
Techniques allow those whom would not be able to reproduce without treatment to have offspring, and very often these offspring carry the same genetic defects that affected their parents. However I do not feel that this affect of medicine can be considered of the utmost concern and neither do I believe it is the sole cause of depletion to the human gene pool. Science may have spawned medicine, but it has also unleashed an industrial and technological revolution that spews out radioactivity and chemicals that can contribute o an increase in our mutation rate-or act directly as selective forces (Cohen, 2001).
Culture itself shapes our genes in various ways. In those societies where milk drinking is an ancient practice, for example, people have genes that allow them to digest the milk sugar lactose. People whose ancestors were not milk-drinkers tend to lack these mutations. Cohen argues that today’s globalisation increases the potential diversity of the human gene pool by bringing together such specialised versions of genes that had been separated through much of history. “This creates new combinations that ay never have been seen before,” he says.
It is quite feasible to see how the decision not to have children, for example, has exactly the same evolutionary impact as losing a child through predation or disease. In this case then we should perhaps not look at medicine as the only factor to which we can attribute the depletion of the human gene pool, others may simply be less apparent to the untrained eye. For the genetic deterioration to occur that would cause severe worry to the human race we are talking many generations and hundreds of years away.
In this time undoubtedly the thics and procedures of genetic engineering will have been debated and resolved, and perhaps this will enable us to either remove genetic defects from the human gene pool entirely or increase diversity ourselves. Although our medicine may seem to us to have great potential to affect the human gene pool in a variety of ways there will surely come a time in the future when our techniques appear crude and inept. For that reason alone I believe that although we have to realise and accept the effects medicine may have on the gene pool, it is important for us to put this effect in context.
