Natural Selection in the Lab

Natural Selection in the Lab: Background Knowledge and Its Role in Evolution of Experimental Systems

Igal Dotan

Background knowledge and its role in scientific research are rather new topics on which very little has been written. Sir Karl Popper, the first philosopher to discuss background knowledge at length, described it as vast amount of information we accept temporarily as unproblematic in a discussion of a given theory. According to Popper, any part of such knowledge is open to challenge. Moreover, it plays an important role in the growth of science as it guides the search for possible refutation, i.e. for the most probable counterexample. Mario Bunge depicts background knowledge as the prevailing outlook and says that scientific knowledge is a product of an endless process of criticism and adjustment between theories and extant knowledge. During this process, researchers try to incorporate new theories into the body of background knowledge, and when they fail, they introduce minor modifications—sometimes of the theory or else of the background knowledge. Joseph Agassi takes background knowledge to be “a mixed bag of working hypothesis, of scientific theories of varieties of levels and metaphysical doctrines, religious superstitions and whatnot.” Agassi’s main emphasis is on the metaphysical doctrines. He claims that scientific research is driven by disputes between competing metaphysical programs, between competing scientific theories within each program, and between scientific theories and metaphysical views.

Igal Dotan’s project aimed to test and discuss the above three theories of background knowledge and to develop an original account of the role of background knowledge in scientific research. It also analyzed the role of false or ignored background knowledge through a case study in which a biological experimental system was criticized and replaced by a new and, allegedly, better one. Although the two experimental systems stemmed from the same theoretical framework, i.e,. neo-Darwinism and population genetics, it appears that the transition had to do with a deeper assimilation of the preexisting background knowledge, and perhaps also with its improvement by theoretical and empirical innovations.

The case in question was the experimental study of natural selection on the fruit fly, Drosophila, under the conditions of a laboratory setup. In this research, populations of flies are either subjected to different kinds of stresses or sorted artificially and monitored for changes in the frequency of one or several life-history traits, i.e., species-specific traits that are assumed to be of relevance for survival. These experiments are devised to test general theories about the evolution and the genetic basis of life-history traits by probing patterns of phenotypic changes and correlations that emerge under specific selection regimes. The fundamental assumption underlying these experiments is that populations subjected to certain environmental conditions (mainly stressful) may reveal their genotypic compositions and structure by exhibiting phenotypic differences due to fitness differences. The trans-generational reaction of populations to novel environmental conditions is also known as adaptation (this process is assumed to be limited by the amount of genetic variation in that population).

Over the last two decades this branch of evolutionary research has become considerably widespread among scholars of evolution and other related areas. From an evolutionary perspective, the researcher’s main interests are phenotypes that exhibit a high degree of (positive or negative) correlation and thus may indicate their evolutionary co-development (e.g., trade-offs between early fecundity and longevity or between resistance to starvation and developmental time). Thus, although adaptation of preexisting genetic variation, used in many laboratory selection experiments, cannot be counted as evolution proper (since no qualitative novelty is introduced), it may indicate traces of evolutionary processes that moulded the species under investigation. Likewise, from an organismal perspective, correlations among several traits may indicate mechanistic relations on various levels (e.g., physiological, epigenetic and genetic).

The program started in the 1950s. In the early 1980s a few prominent researchers, notably Michael Rose, Brian Charlesworth, and Philip Service, began questioning some basic theoretical and methodological assumptions of this program and suggested a radical reconstruction of the experimental system for laboratory selection experiments. Their main contention was that results obtained to that point by selection experiments were unreliable due to lack of control of various genetic, environmental, and behavioral factors (e.g., genetic heterogeneity of base population, uncontrolled density and inbreeding) as well as to weaknesses in the experimental design (e.g., population size, selection periods, and replication at population level). Remarkably, long before the 1980s, population geneticists had acknowledged that these factors might have diverse effects on population dynamics. In fact, this knowledge was part and parcel of the empirical and theoretical background knowledge of population genetics in particular and of evolutionary biology in general. Nevertheless, it seems that researchers ignored this in their empirical research, or else were not able to use this knowledge in order to improve their experimental systems.

This raised two questions that were addressed by this project. The first question was historical: What, if anything, was missing during the first period of laboratory selection experiments so that almost three decades passed before researchers were willing or able to revise their experimental systems according to biological background knowledge that had long been available? The second question was methodological: How and to what extent did the new program assimilate (previously ignored) background knowledge within the experimental system of laboratory selection, and conversely how and to what extent did the biological background knowledge change due to the new experimental system?