Overview

Harvard evolutionary biologist and Modern Synthesis architect Ernst Mayr (1961) wrote about biological causation, distinguishing between proximate and ultimate causes. Mayr equated proximate causation with immediate factors (e.g. physiology) and ultimate causation with evolutionary explanations (e.g. natural selection). He argued that proximate and ultimate causes addressed different questions and were not alternatives, which remains a valid and non-contentious point.

Mayr’s account of causation remains widely accepted today, with both positive and negative ramifications. One negative consequence was that Mayr insisted on a strict separation of proximate and ultimate causes:

“The clarification of the biochemical mechanism by which the genetic program is translated into the phenotype tells us absolutely nothing about the steps by which natural selection has built up the particular genetic program” (Mayr 1980).

This position was based upon a specific view of development:

“All of the directions, controls and constraints of the developmental machinery are laid down in the blueprint of the DNA genotype as instructions or potentialities” (Mayr 1984).

Mayr and his followers argued that developmental (i.e. ontogenetic) processes were irrelevant to the study of evolution. Niche construction is an ontogenetic process, and advocates of the niche-construction perspective, alongside others, have taken issue with Mayr’s treatment of causation (Laland et al. 2011).

For Mayr, developmental processes could not be regarded as independent causes of evolutionary events, since he believed their properties (which include how organisms construct their niches) were themselves fully explained by prior natural selection. From Mayr’s standpoint, if developmental processes direct evolutionary events, this is only the proximate manifestation of the ultimate cause of natural selection; aspects of development not shaped by selection were assumed to play no evolutionary role.

This stance has made it more difficult for evolutionary biologists to recognize niche construction as an evolutionary process. Niche construction is perceived to have no independent evolutionary significance because, to the extent that it is evolutionarily consequential, it is regarded as fully explained by a preceding cause, natural selection (e.g. Dawkins 2004).  Niche-construction effects are treated as ‘extended phenotypes’, whose sole evolutionary role is to affect the probability that gene variants underlying niche construction are passed on to the next generation. Similar reasoning underlies the treatment of niche construction as an indirect genetic effect, with, for example, a mother’s genes affecting her offspring’s phenotype by modifying its environment (Wolf et al. 1998).

There are two major problems with this line of reasoning:

First, as described above, the processes underlying variation, fitness and inheritance are causally intertwined. All organisms have always engaged in niche construction, going right back to the beginning of life. Hence there is no reason to assume that natural selection must be the first cause of any evolutionary episode. Causation in biological systems is reciprocal rather than linear, with natural selection and niche construction codirecting each other.

Second, not all evolutionarily consequential aspects of niche construction (nor all aspects of development, in general) are under genetic control. Niche-construction theorists, like many developmental biologists, regard organisms (and their environmental modification) as under-determined by genes. The changes that organisms bring about do not flow only from their adaptations, but also derive from plasticity, byproducts, and acquired characters.