Sunday, February 21, 2016

The Human Nature of Genetic Engineering: A Realistic Assessment of CRISPR

For over fifty years, some people have been predicting that someday genetic engineering will radically transform, perhaps even abolish, human nature, and thus lead us to what Francis Fukuyama has called "our posthuman future."  The transhumanist optimists (people like Ray Kurzweil, Gregory Stock, and Nick Bostrom) have welcomed this prospect for transcending the limits of human nature.  The bioconservative pessimists (people like Fukuyama, Leon Kass, and Bill McKibben) have warned against this as biotechnological suicide.

Until recently, the existing technology for manipulating the human genome has not been powerful enough or precise enough to do this.  But now, a new technique seems to offer the prospect that parents might be able for the first time to modify the genetic nature of their offspring to create “designer babies,” and then these genetic changes could be passed on by biological inheritance so that the nature of the human species itself might be fundamentally altered, if not abolished.

And yet, a realistic assessment of the potential for genetic engineering should show us that both the transhumanist optimists and the bioconservative pessimists are mistaken, because they fail to see how genetic engineering will always be so limited in both its technical means and its moral ends, that it cannot change human nature.

The new technology for editing DNA that has stirred excitement and controversy over the past three years is called CRISPR, the acronym for “clustered regularly interspaced short palindromic repeats.”  Some years ago, scientists discovered that the DNA of some microbes had some identical segments of DNA composed of repeated sequences of the same bases, the building blocks of DNA.  These repeated segments were separated by blocks of DNA, called spacers, which had a unique sequence.  Scientists also noticed that these CRISPR sequences were always accompanied by nearby genes called Cas genes (“CRISPR-associated genes”).  Once they saw that the CRISPR spacers looked like the DNA of viruses, scientists could infer that CRISPR was part of the microbe’s adaptive immune system for destroying viruses. 

When viruses invade microbes, many of the microbes die, but those that survive will grab some of the virus’s DNA and insert it into a CRISPR spacer.  The microbe can then use this viral DNA to identify future viral invaders and target them for destruction.  Cas enzymes are guided to viral DNA and then chop it up, so that the virus cannot replicate.  Scientists discovered that they could use this CRISPR-Cas system to enter a cell, snip out any segment of DNA that they targeted, and then have the cell stitch a new gene into the open space.  Moreover, they could do this not only for somatic cells, but also for germ cells (eggs and sperm).  Doing it for germ cells would mean that the genetic changes would be passed down by the biological inheritance of offspring.  Recent research has shown that this can be done with human embryos.  This suggests the possibility that parents could use this technique to genetically enhance their children with genetic propensities for better bodies and better minds, and that this redesign of the human genome could be passed down by inheritance to the next generation.

Properly understood, this should teach us at least three lessons about human evolution—lessons about the Lamarckian character of biological evolution, about the natural sources of technological evolution, and about how evolved human nature limits the power of genetic technology.

First, notice that CRISPR is an adaptive immune system that learns from its experience with the viral enemies of microbes and passes on what it has learned to the descendants of the microbes.  It has been generally assumed that Jean-Baptiste Lamarck’s theory of the evolutionary inheritance of acquired traits has been refuted by Darwinian biology.  Actually, Charles Darwin himself accepted Lamarckian evolution as one of the mechanisms of evolutionary change.  And CRISPR shows that Lamarckian inheritance really does occur in nature.  Using CRISPR for the genetic engineering of children could become a form of intentional evolution in which parents use scientific knowledge and technology to direct the evolutionary inheritance of acquired traits for the improvement of human life.

The second lesson here is about the natural sources of the technological evolution of genetic engineering.  We might see genetic engineering as manifesting the modern scientific project, first proposed by Francis Bacon in the seventeenth century, for the human mastery of nature for the relief of the human estate.  We might think that such a conquest of nature requires the human invention of artificial tools.  But notice that CRISPR is not a human invention but something that scientists discovered in nature.  Microbes have been using CRISPR to edit their DNA for millions of years.  Once we understand how this works in nature, we can then use it for genetic engineering.  This confirms Bacon’s observation that “nature to be commanded must be obeyed,” because “all that man can do is to put together or put asunder natural bodies,” and then “the rest is done by nature working within.”  And thus we should see how the power of biotechnology is limited by the potentialities inherent in nature.

That leads us to the third lesson—how evolved human nature limits the power of genetic technology.  A realistic assessment of genetic engineering avoids both the exaggerated hopes of the optimists and the exaggerated fears of the pessimists, because we should see that genetic engineering will always be limited in its technical means and its moral ends.

It will be limited in its technical means, because an individual's traits of personality and intelligence arise in unpredictable ways from a complex interaction of genes, brains, life history, and social environment that is not determined by one or a few genes.  Genetic engineering can possibly eliminate some genetic disorders that are strongly influenced by a few genes.  But the complex traits of the human mind are not genetically determined in any simple way.

For example, proponents of human genetic engineering often say that it will allow parents to increase the innate intelligence of their children by selecting those genes that enhance intelligence.  But while there surely is some genetic contribution to human intelligence, research in behavioral genetics suggests that intelligence arises as much from environmental factors as from genetic propensities.  Moreover, the genetic basis of intelligence depends on so many genes interacting in such complex ways that it will be impossible to control this through changes in one or a few genes. 

Even if we could explain exactly the multiple genetic causes of intelligence, we would still have to explain how these genes influence neural activity and how genetic propensities and neural activity interact with environmental contingencies in the unique life histories of particular human beings.  And all of this would presuppose that we could agree on how to define and measure “intelligence,” even though both scientific research and common-sense experience suggest that there are different kinds of intelligence—for example, analytic intelligence, verbal intelligence, practical intelligence, musical intelligence, and kinesthetic intelligence.  For all of these reasons, we are unlikely to ever succeed in the genetic engineering of intelligence.

Genetic engineering will also be limited in its moral ends, because parents will want to use this technology to improve the chances that their children will be healthy and happy, and thus the parents will be guided by the same natural desires of our evolved human nature that have always motivated parents in the care of their children.

For these reasons, we should welcome genetic engineering as helping us to treat some genetic disorders, but we should not expect that it will ever fundamentally transform human nature.  We should give up both the utopian hopes of the transhumanists and the apocalyptic fears of the bioconservatives.

Some of my previous posts criticizing genetic determinism can be found here, here, here, here, and here.

1 comment:

Anonymous said...

When TV was invented optimists claimed that it would usher in a golden age of education, but it just produces trash.
The internet was supposed to create a global village of brotherhood, but something like 60% of traffic is porn.
My guess is parents will want the crassest things for their children, mostly to increase sexual attractiveness. This might even eventually end up with an Irish Elk situation of ridiculous extents of a sexual arms race.