Life history theory
Life history theory is a collection of hypotheses in evolutionary biology that explain why animal species differ in so-called life-history traits. These traits include body size (including size at birth), growth and developmental schedules, the number, size, and sex ratio of offspring, reproductive schedules, sex drive, lifespan, extent of investment in the offspring and, in social species, level of pro-sociality and competition with other groups. The most prominent of these hypotheses that attempted to explain why species differed in these life-history traits was developed from the evolutionary biologist E.O Wilson's r/K-selection theory. This theory stated that species vary on these life-history traits depending on the selection pressures in terms of reproductive scheduling exerted by their local ecology.
Organisms were conceptualized to exist on a "fast-slow" spectrum that explains variations in these physiological traits, called their life history speed. Essentially species could either adopt a more qualitative or a more quantitative approach to reproductive scheduling. R-strategist species (from the slope of the line in biological models modeling population growth, with r representing exponential growth) are adapted to unstable ecologies where the evolutionarily optimal strategy is to produce as many offspring as possible. They also invest little bioenergetic resources into somatic effort, (development and the maintenance of body systems) and typically have brief lifespans. K-strategist species (from the German word for capacity, Kapazität) are evolved in a stable but harsh ecology that has reached its carrying capacity in terms of population growth. In such ecologies, the optimal evolutionary strategy is to invest more in physiological development and maintenance and limit reproduction, focusing more on the viability of the offspring by investing heavily in them in terms of nurturance.
Owing to this model's potential predictive power and its importance to evolutionary biology as a whole, evolutionary psychologists (and other social scientists) eventually seized on the concept of animal species existing on a fast/slow life history spectrum. They applied it to explain variations in human behavior, both among individuals and among broad racial groups (J.P Rushton's controversial differential-K theory). While the social sciences' adoption of life history theory has proven controversial, many argue that it exhibits strong consilience (the synthesis of knowledge from disparate fields, in pursuit of a "universal theory of everything") and parsimony in explaining individual differences in a broad suite of physiological and behavioral traits. Many of these traits do correlate with each other along the lines predicted by life history theory models. Critics, on the other hand, tend to argue that the application of a singular slow/fast spectrum to human variation in life-history traits is overly simplistic, that individuals adapt to their environment differently than species, that the application of LHT to human behavioral traits is internally inconsistent, and that the application of LHT to human traits by psychologists is too broad.
Though humans are a K-adapted species, it seems likely that individual humans (and even whole cultures and societies) differ in life-history speed, either genetically or in response to environmental demands. Thus life history theory can prove to be a useful predictive model for explaining human variation in traits such as age at first intercourse, mating effort, mating displays, level of intrasexual competition, pair-bonding ability, cognitive abilities, reproductive decisions, physical appearance, personality traits, and levels of aggression; in short, all things highly relevant to the discussion of the causes of involuntary celibacy.
r/K-selection[edit | edit source]
r/K selection is one hypothesis that attempts to explain how and why species differ on life history traits, adding additional mechanisms explained in the sections below (tbd). At the core of r/K selection is a distinction between two kinds of ecologies which are opposed on the spectrum of ecological harshness:
- Unpredictable, but easy ecologies, e.g. tropical regions are full of competing predatory animals, but food is readily available (e.g. fruits and smaller animals). Animals in such ecologies are said to be r-selected, where r is the growth rate and r-selected means maximizing growth rate. This means making as many offspring as possible and not investing much in them, hoping they will make their way through the unpredictable but easy environment, i.e. requiring little guidance on part of the parents. R-strategists have a fast life history (speed).
- Predictable, but harsh ecologies, e.g. cold regions have relatively low population counts as food is hard to attain through the winter. Animals in such ecologies are said to be K-selected, where K is the carrying capacity of the environment. In harsh ecologies this capacity is low, so species produce few offspring and care for them, and maintain the population size near the maximal carrying capacity. K-selected species evolve "K-strategies" that emphasize high levels of parental care, resource acquisition, kin provisioning, and social complexity. The K-strategy requires more complex nervous systems and larger brains. K-strategists have a slow life history.
In summary, an unpredictable but easy ecology favors quantity, while a predictable but harsh environment favors quality.
Sex differences[edit | edit source]
Women's sexual strategy is overall slower than men's which is primarily evidenced by their more coy and passive sex drive, lower promiscuity, lower engagement in short-term relationships, more limited reproductive rate, higher neoteny, lower violence, lower activity levels and higher life expectancy. Nonetheless, there is a fair amount of interindividual variation with a minority of women even willingly engaging sex with strangers. Moreover, women paradoxically exhibit fast-life strategies in some regards, especially in that women tend to lose interest in long-term romantic investment much sooner than men and yield nearly the same rate of affairs. In fact, biochemical research points to a natural four-year sexual cycle for the human female. A woman’s natural tendency is to “liberate” herself from her mate after that point. This is in line with divorce statistics where women are the initiator 75% of the time. Moreover, women mature sooner than men, with early maturation being a key aspect of fast LH predisposition. This, however, may simply be a result of men selecting for neoteny for paternity assurance or due to women getting easier access to resources by looking cute.
So, even though women's life history speed is slower in terms of reproductive rate and choosiness, their long-term strategy seems to be actually less r-selected than men's, implying less long-term investment in the offspring and hence less compatible with modern, highly ordered and structured civilization.
This sex difference may also stem from the fact that women have overall been less subject to selective pressures as they reproduced twice as often as men. For this reason, women's sexuality may be stuck in a more r-selected past. Women's tendency to switch mates has also been explained by the mate switching hypothesis as a means to ensure a suitable provider and protector all the time, which women are thought to depend on especially in the more ancient, fast ecologies (bodyguard hypothesis). Another explanation could be that modern mating conditions are an evolutionary mismatch due to women being economically independent and liberated such that their hypergamy, choosiness and fickleness becomes more exposed. This is evidenced by the fact that arranged marriage used to be much more prevalent than it is today, so women's own choices may have never been subject to much selection pressure as it was largely overridden by parental choice.
Women's lower capacity of forming long-term friendships, as evidenced by their higher rate of gossipy and destructive intrasexual competition, is also indicative of a faster life history speed, as such behavior is not aimed at furthering long-term investment and social cohesion.
References[edit | edit source]
- https://toqonline.com/archives/v7n2/v7no2_Devlin.pdf (Langley 2005)
See also[edit | edit source]
- Reproductive success
- Dark triad
- Borderline personality disorder
- Nice guy