Germline changes – an ethical dilemma.
Whether you do regular exercises, or dye your hair, or get a tattoo, or have cosmetic surgery, these changes will have no effect on any offspring you might have. Whether you develop cancer or freckles, none of this has any effect on the following generation. However, each individual produces special cells called gametes (eggs and sperm) with only half of the genetic information in normal adult cells. Only the egg and sperm are able to determine the characteristics of a person’s offspring. The gametes are produced in special organs called ovaries in females and testes in males.
Changes in the gametes are called germ line changes because they affect future generations. Changes in the normal genetic material of the gamete cell are rare, but they do occur occasionally when the gametes are produced. Naturally, future generations will be affected by such changes.
If a scientist however inserts a change into a fertilized egg, that cell will develop into a whole new individual including the sex organs which will in due course produce gametes. Those gametes will reflect the changes to the fertilized egg of what has now become a potential parent. So, germ line changes affect future generations but changes to somatic [normal adult cells] will not.
Engineering a change to the germline of an individual is therefore a serious ethical issue because, for good or ill, it can potentially affect many future generations.
Recently scientists have set out to investigate if there is a difference in mutation rates between the somatic cells and the germline cells. For example, see [Luiza Moore et al. 2021. The mutational landscape of human somatic and germline cells. Nature 597 #7876: 381-386.] In this article the scientists point out that “mutations in the germline can be transmitted to the next generation, making them the raw material of species evolution and the cause of hereditary diseases.” [p. 381] While many people suppose that mutations provide the raw material for evolution, in reality, mutations are a serious source of congenital diseases. The authors of the article also report, from other studies, that 80% of inherited germline mutations come from the male (paternal) line. [p. 381]
In their study, these scientists compared mutations within the somatic tissue and germline cells of single individuals. The authors found that the mutation burden within germ cells of the testis was 27-times lower than within somatic cells. [p. 385] They further declared that the low germline mutation rate is “an intrinsic feature of the male germline compared with the soma.” [p. 386] Moore et al. further suggesedt that there must be superior mechanisms to maintain genomic integrity in the germline cells. [p. 386] The scientists concluded that “the germline has found ways to limit the mutagenesis” [p. 386] a talent not shared by somatic cells. This situation struck them as “unexpected and mysterious” since they would normally expect similar processes in both somatic and germline cells.
It is evident that there is a conflict between evolution theory and reality. The ideal situation for evolution is the appearance in the germline of many mutations from which natural selection may select the best mutations. Contrary to this idea is the need for organisms to protect their offspring from harmful mutations which can cause decline and extinction.
The question arises as to the source of special protection for germline cells. Evolutionary processes have no foresight to know that such protection is needed. Indeed, it is in the interests of the evolutionary process to favour more mutations, not fewer. But in the face of all those deleterious mutations, this would be the road to disaster for the population. In this protection of the germline cells, we see planning and purpose.