The E-volution Heuristic
The basic idea is simple. In order to decide whether we want to modify some aspect of a system, it is helpful to consider why the system has that aspect in the first place. Similarly, if we propose to introduce some new feature, we might ask why the system does not already possess it.
The system of concern here is the human organism. The question why the human organism has a certain property can be answered on at least two different levels, ontogeny and phylogeny. Here the focus is on the phylogeny of the human organism.
We can conceive of a proposed enhancement as an ordered pair (a, A), where a is some specific intervention (e.g., the administration of a drug) and A is the trait that the intervention is intended to realize (e.g., improved memory consolidation). We define an enhancement as an intervention that causes either an improvement in the functioning of some subsystem (e.g., long-term memory) beyond its normal healthy state in some individual or the addition of a new capacity (e.g., magnetic sense).
On this definition, an enhancement is not necessarily desirable, either for the enhanced individual or for society. For instance, we might have no reason to value an enhancement of our sweat glands that increases their ability to produce perspiration in response to heat stimuli. In other instances, we might benefit from increased functionality or a new capacity and yet not benefit from the enhancement because the intervention also causes unacceptable side effects. The evolution heuristic is a tool to help us think through whether some proposed enhancement is likely to yield a net benefit.
The starting point of the heuristic is to pose the evolutionary optimality challenge:
(EOC) If the proposed intervention would result in an enhancement, why have we not already evolved to be that way?
Suppose that we liken evolution to a surpassingly great engineer. (The limitations of this metaphor are part of what makes it useful for our purposes.) Using this metaphor, the EOC can be expressed as the question, “How could we realistically hope to improve on evolution’s work?” We propose that there are three main categories of possible answers, which can be summarized as follows:
- • Changed tradeoffs. Evolution “designed” the system for operation in one type of environment, but now we wish to deploy it in a very different type of environment. It is not surprising, then, that we might be able to modify the system better to meet the demands imposed on it by the new environment. Making such modifications need not require engineering skills on a par with those of evolution: consider that it is much harder to design and build a car from scratch than it is to fit an existing car with a new set of wheels or make some other tweaks to improve functioning in some particular setting, such as icy roads. Similarly, the human organism, while initially “designed” for operation as a hunter-gatherer on the African savannah, must now function in the modern world. We may well be capable of making some enhancing tweaks and adjustments to the new environment even though our engineering talent does not remotely approach that of evolution.
- • Value discordance. There is a discrepancy between the standards by which evolution measured the quality of her work and the standards that we wish to apply. Even if evolution had managed to build the finest reproduction-and-survival machine imaginable, we may still have reason to change it because what we value is not primarily to be maximally effective inclusive-fitness optimizers. This discordance in objectives is an important source of answers to the EOC. It is not surprising that we can modify a system better to meet our goals, if these goals differ substantially from the ones that (metaphorically might be seen as having) guided evolution in designing the system the way she did. Again, this explanation does not presuppose that our engineering talent exceeds evolution’s. Compare the case to that of a mediocre technician, who would never be able to design a car, let alone a good one, but who may well be capable of converting the latest BMW model into a crude rain-collecting device, thereby enhancing the system’s functionality as a water-collecting device.
- • Evolutionary restrictions. We have access to various tools, materials, and techniques that were unavailable to evolution. Even if our engineering talent is far inferior to evolution’s, we may nevertheless be able to achieve certain things that stumped evolution, thanks to these novel aids. We should be cautious in invoking this explanation, for evolution often managed to achieve with primitive means what we are unable to do with state-of-the-art technology. But in some cases, one can show that it is practically impossible to create a certain feature without some particular tool—no matter how ingenious the engineer—while the same feature can be achieved by any dimwit given access to the right tool. In these special cases, we might be able to overcome evolutionary restrictions.
In the following three sections, we will explore each of these categories of possible answers to the EOC in more detail and show how they can help us decide whether or not to go ahead with various potential human enhancements.
Our ideas about enhancement in many ways parallel earlier work in evolutionary medicine. Evolutionary medicine is based on using evolutionary considerations to understand aspects of human health (Willams and Nesse 1991; Trevathan et al. 1999). Hosts and parasites have adapted to one another, and analysis of the tradeoffs involved can reveal adaptations that contributed to fitness in the past but are maladaptive today or symptoms that have been misdiagnosed as harmful but may actually aid recovery. Evolutionary medicine also helps explain the incidence of genetic diseases, which can be maintained in the population because of beneficial effects in historically normal environments. Another contribution of evolutionary medicine has been to draw attention to the fact that our modern environment may not always fit a biology designed for Pleistocene conditions and how this mismatch can cause disease. These insights are recycled in our analysis of human enhancement.
Another strand of research relevant to our aims is evolutionary optimization theory, which seeks to determine the abilities and limitations of evolution in terms of producing efficient biological functions (Parker and Smith 1990). While, naively, evolution might be thought to maximize individual fitness (the expected lifetime number of surviving offspring), there are many contexts in which this simplification leads to error. Sometimes it is necessary to focus on the concept of inclusive fitness, which takes into account the effects of a genotype on the fitness of blood relatives other than direct decedents. Sometimes a gene-centric perspective is needed, to account for phenomena such as segregation distortion and junk DNA (Dawkins 1976; Williams 1996/1966). There are also many other ways in which evolution routinely falls short of “optimality,” some of which will be covered in later sections.
-  Which side effects are acceptable depends, of course, on the benefits resulting from the enhancement, and these may vary between subjects depending on their goals, life plans, andcircumstances.