We will now look at a different classification of evolutionary processes: the distinction between the so called r- selection and K-selection (E.O. Wilson 1975).
If a species lives under conditions where resources are ample so that there are good opportunities for expansion, but where there is also considerable dangers such as predators, then it will pay for this species to use most of its resources on breeding as fast as possible. This is called r-selection. The r is the mathematical symbol for the rate of reproduction. r-selection causes the evolution of small organisms growing fast and breeding fast. Examples are mice and insects.
The opposite of r-selection is K-selection. This is what happens when a species lives in an overcrowded environment where the population is limited by the available resources rather than by predation. The capital K is a mathematical symbol for carrying capacity, i.e. the maximum number of individuals that the resources in a given habitat can
continually sustain. K-selection leads to the evolution of big animals which breed slowly and utilize the given resources optimally, and which invest a considerable proportion of their resources in the care of their sparse offspring. K-selection is found in those animals that come last in a food-chain, such as whales, elephants, and humans.
The r/K-scale has also been widely used for classifying reproductive strategies. An r-strategy is the strategy of an animal which breeds fast and produces numerous small offspring, but does not care for its offspring. A K-strategy involves late breeding, the production of few big young, and a diligent care for the sparse offspring. The r-strategy is advantageous when predation or other disturbances limit the population below the carrying capacity of the environment, so that there is always plenty of food. The K-strategy is the optimal strategy when the environment is crowded and the population size is limited by the scarcity of food or other resources.
The r/K-theory has been criticized because its theoretical foundation is over-simplistic, and because most of the variation in the parameters which are assumed to be connected with the r/K-scale is found to be a variation between lineages rather than between species in the same lineage or variation within the same species (Stearns 1992). A satisfactory theoretical explanation of the connection between various traits is sometimes lacking, especially in the case of K-selection (Boyce 1984).
However, even critics of the theory have to admit that the theory has merits:
"Enough people have found it a useful framework in which to interpret their observations that it must contain an element of truth. The problem is to identify that element." (Stearns 1992).
The theoretical difficulties notwithstanding, there remains a significant correlation between the important traits, even when factors which might be seen as confounding are corrected for (Stearns 1992), and there have been several attempts to improve the model in order to bring theory in accordance with observations (Boyce 1984, Taylor et al. 1990, Kozlowski & Janczur 1994).
I will argue that the explanatory power of the r/K-theory is easier to account for when the theory is re-interpreted in terms of selection criteria. When the population size is small due to predation or other adversities, but food and other resources are plentiful, then the main selection criterion will obviously be the quantity of offspring. The optimal reproductive strategy will be to breed as fast as possible and produce as many young as possible, rather than spending resources on growing. In the opposite situation, where the population size is limited only by the carrying capacity of the environment, there will be a fierce competition for food, and the animals should be expected to develop competitive abilities. Body size will often be a decisive factor in the competition with conspecifics, and the optimal strategy will therefore be to spend more resources on growing big and fewer resources on breeding. The young are necessarily smaller than the adults and therefore have a disadvantage in the competition for food unless they are helped by their parents. Hence the evolution of parental care, and hence the production of few big young rather than many small. The process may be seen as self-amplifying because big animals are less vulnerable to predation and therefore more likely to be limited by the availability of food and other resources than by predation. By re-interpreting the r/K-theory in terms of selection criteria here, i have made it more intuitively acceptable. Since the direction of evolution is determined by selection criteria regardless of mechanisms, the sometimes incomplete understanding of the mechanisms behind r- and K-selection becomes less problematic.
The fact that most of the variation in these traits is observed to be a variation between lineages rather than within species, as Stearns (1992) objects, can easily be explained as a consequence of genetic barriers, as defined on page 75. The genetic variation within a species or lineage may be insufficient for adapting to a radical change in r/K- conditions because of genetic barriers. In this case the niche is more likely to be colonized by a different lineage whose traits lie closer to the optimum for that particular niche.
4.4 Cultural selection models
In cultural selection theory, the number of possible models is far greater than for the genetic processes, because both innovation, reproduction, and selection of cultural phenomena may involve many different mechanisms. All these mechanisms may interact with each other in so many complicated ways that a stringent account and classification of possible cultural processes is hardly possible, and it is even more questionable whether this would be a useful approach in applied social research.
Rather than building a taxonomy of cultural processes on selection mechanisms, i have chosen to base my classification on the social forces that give rise to selection, and the corresponding selection criteria. This principle is analogous to the abovementioned distinction between r- and K-selection in genetic evolution. I am using this shortcut not only to avoid intractable mathematical problems, but also because i consider the direction of evolution more interesting than its speed - and the direction of evolution is indeed determined by the selection criteria.
Cultural selection theory is still in its infancy, and what we need at this stage is general models which can provide a broad outlook. The reductionist approach of analyzing the details of one particular cultural selection mechanism among many would not lead to the general understanding of a complex society. Biological evolutionary theory has previously benefitted a lot from the r/K-theory but has now come to a stage where the r/K-theory seems too simplistic. The theory of cultural selection has not yet come to such a stage, and therefore a simplistic model is justified.
As will be evident from the following chapters, this approach has turned out to have an explanatory power far superior to that of previous selection models. Of course, i do not deny that other classification principles may have valuable applications.