These subjects are a key part of any discussion of future human evolution, leaving aside possible Lamarckian effects, because it will become impossible to differentiate between 'natural' and 'artificial' biological processes at the genetic level. The 'tweaking' of genetic formulae for plants such as wheat to produce improved varieties, and the introduction of genetically-manipulated disease resistant strains of domestic animal, however much resistance they have encountered from 'whole earth' activists (and is it really so different from the domestication of wolves?) are evidently the forerunners of comparable improvements to the human genome. This, and its ethical consequences, will be dealt with more thoroughly in the next section; but here we just need to note that there is no conceptual difference between the alteration in an embryo of the gene that expresses for Huntingdon's chorea and the introduction of a genetic sequence which lengthens the bones of the foot and may produce lots of 'Thorpedos' (the Australian Olympic swimming medallist who has unusually large feet).
Genetically engineered drugs are already in common use, although they were controversial at first. Genetically-engineered human insulin was approved by the USA's FDA in 1982; genetically engineered human growth hormone as replacement for a drug that was previously extracted from human cadavers was another early use. In 1986 the FDA approved the first genetically engineered vaccine for humans, for hepatitis B. Since these early uses of the technology in medicine, the use of genetic engineering has expanded to supply many drugs and vaccines, as well as its use in the food chain, which remains controversial in many parts of the world, although no longer among scientists.
Gene therapy, in the sense of the delivery of 'good' or 'curative' dna into humans in order to cure or ameliorate genetically-caused conditions, is also already widely practised. It affects only the 'somatic' dna rather than the 'germ-line' dna, and is therefore not transmissible to children. It is a blunt weapon, and perhaps will never be otherwise, because of the difficulty of replacing all of the errant dna in a body on a continuing basis. For some localized conditions affecting only specialized types of cell, that can happen, but in most situations treatment has to be ongoing and is never more than partial.
Existing gene therapy could therefore be seen as a stop-gap measure pending the application of germ-line therapy at the embryonic stage. The problems in introducing germ-line therapy are by now at least as much ethical as practical. What is acceptable today in therapeutic terms, such as in vitro fertilization and the selection of early-stage embryos to head off diseases and to select the sex of a child, stops short at the 'improvement' of the human genome on a more systematic basis.
The techniques for more direct interference with the dna of an embryo already exist, however, and have been tested in animals. See Appendix Five for a fuller account of the current state of such technologies.
Scientists and legislators are hesitating before permitting changes to be made to human embryos. Many of them are completely against it, so that while it seems a certainty that it will come to pass, it is difficult to know the time-scale.
It will take another few years (until 2020, say) for medical researchers to establish safe in vitro fertilization practices, based on statistical studies; but after that it will be hard for governments to justify holding back permission for remedial dna manipulation. The mechanism of expression of the various genes and accompanying 'nonsense' dna, mitchondrial filaments, etc, will have been worked out to a high degree by 2030, at least as regards those attributes which are particularly desirable or undesirable.
Given the impossibility of distinguishing between what is remedial and what is 'improvement' (as explained above in the 'bionics' section) it will then be only a matter of time before 'improvement' becomes routine, at least within the parameters of what is normal. Such attributes as height, eye colour, size of organs (you can guess which will be the most popular), propensity to obesity, propensity to drug addiction (these last two presumably remedial), facial symmetry, hair colour and texture, bodily hair growth, length of fingers, width of palm (for pianists), might all be mutable via reasonably straightforward genetic adjustment.
No doubt some form of supervisory body will come into existence which will arbitrate over doubtful cases, and set the limits to what is permissible and what is not; and no doubt over time the boundaries will stretch. It will be hard to prevent people from achieving cheaply through dna manipulation what they could achieve through bionic implantation, although the latter will be ethically much easier to defend. Improved eyesight for instance, could probably be delivered either way, but surely it's cheaper just to tweak the dna than have a US$30,000 operation to instal a corneal implant?
It is a less straightforward question, given the present state of our knowledge, whether the role of dna mechanisms in the formation and expression of social behaviour could or should be directly manipulated. This issue is addressed in the next section.