Every single human is born with a packet of the total human genome. The mating strategies people use in their lives are heavily influenced by the unique genetic packet they inherited from their personal lineage (dating back to their earliest ancestors at the dawn of human evolution) interacting with their immediate environment. The complex interplay between genes, neighborhood influences (peers, general climate), and family support that contributes to the development of an individual's life history strategy is fascinating and highly nuanced. Let's start with the genes.
What's the evidence showing that the packet of traits and behaviors that make up the fast life has a genetic basis? Accessing a database that included a nationally representative sample of 309 identical twins and 333 fraternal twin pairs aged 25-74, Figueredo and colleagues (2004) analyzed 30 scales of life history traits (e.g., quality of family relationships, altruistic behaviors), medical symptoms (e.g., thyroid disease, ulcer), personality traits (e.g., neuroticism, extraversion, conscientiousness, openness to experience), and social background (e.g., financial status).
They found that all the items were moderately related to each other and formed a higher-order "K-factor" (see Part I, Evolution of the Fast Life). Individuals scoring higher on the K-factor tend to live a slower life whereas those scoring lower on the K-factor tend to live a faster life. This higher-order K-factor explained most of the genetic correlations among the scales, was 68% heritable and accounted for 82% of the genetic differences among the lower-order factors. According to the researchers, these results suggest that "Life History Strategy might be heavily influenced by regulatory genes that coordinate the expression of an entire array of life history traits."
Regulatory genes don't just activate themselves, however. They require environmental triggers or else they won't be expressed. What are the important environmental triggers?
Harsh and Unpredictable Environments
Analyzing a nationally representative database that followed up thousands of adolescence
from youth to young adulthood, Brubach, Figueredo, & Ellis (2009) found that two environmental factors in particular explained a considerable amount of the differences found in life history strategy (e.g., the K-factor).
Both environmental harshness ("self-reported exposure to violence from conspecifics") and unpredictability ("frequent changes or ongoing inconsistency in several dimensions of childhood environments") independently explained a large part of the variation in a K-factor consisting of an intertwined number of life history traits such as mental and physical health, relationship stability, sexual restrictiveness, social deviance, and economic success. Life history traits in adolescence were fairly stable across time and were significantly related to life history strategy in young adults. According to the researchers,
"...by the time people reach their mid-twenties, they have formed a coherent life history strategy that is characterized by their overall health, approach to romantic and sexual partners, and the amount of effort they have put into education and employment."
While it is clear what it means to live in a harsh environment (exposure to mortality and violence has a clear definition), it's not so obvious what the specific unpredictable elements of the environment are that most strongly influence the development of an individual's life history strategy. A number of important studies in the past 20 years or so have looked to the early family environment for clues.
A child's home environment can play a significant role in an individual's life history strategy. While it is certainly true that human parental investment is extremely high compared to other species (Flinn & Ward, 2005), there are many circumstances in which children are raised in unpredictable family environments with little parental care. Various studies, including those that have controlled for the effects of genetic transmission, show that stressful parent-child relations and negative parenting
have a significant effect on pubertal timing. This effect seems to be strongest for girls, although family stress
can accelerate adrenarche
in males as well (see Belsky et al., 2007; Ellis & Essex, 2007; Tither & Ellis, 2008).
There is also research on the effects of total parental absence on the development of life history strategy. Since father absence is more common than mother absence, and shows higher cultural variability (there are "father-absent" and "father-present" societies but no consistent "mother-absent" societies), a particularly active area of investigation is the consequences of father absence on the development of an individual's life history strategy.
In general, when father's don't invest in parental care, there is a tendency for boys to live the fast life- increased delinquency, aggression, and other indicators of high mating effort (Figueredo, Brumbach, Jones, Sefcek, Vasquez, & Jacobs, 2008). Since it easier to osberve a clear-cut landmark of sexual maturation in girls (e.g., age of first menstrual cycle), there is considerably more research on the effect of father absence on girls. Women also tend to remember the age of their first menstrual cycle which allows for retrospective studies.
In an important review of the literature, Ellis (2004) presents evidence that girls who grow up in a home where the father is absent or negligent in their parenting are more likely to go through their first menstrual cycle (i.e., "menarche") by the age of 12 compared to their peers. In fact, the age in which "father-absent girls" tend to go through menarche is related to the number of years of father absence, the amount of time fathers spent taking care of daughters during the first five years of life, and the amount of affection observed in parent-child relationships.
The behavioral and psychological correlates of having a father absent for girls run far and wide, tending to trigger traits and behaviors typical of the fast life such as rapid sexual development, increased fertility, lower adult attachment to romantic partners, greater levels of manipulative and exploitative attitudes, less parental care devoted to one's offspring, greater risk-taking behavior, higher incidence of affective disorders, social aggression, sexual promiscuity, and preference for sexual variety.
Framing the effects of parental absence on life history strategy in an evolutionary context, Belsky et al. (1991) and Chisholm (1993) argue that children in the first few years of life use their level of attachment security as a cue of risk and uncertainty, and this then influences the development of their reproductive strategy. A safe and predictable environment (neighborhood, social, and parental) will trigger a slower reproductive strategy, with a focus on later reproduction and high parenting effort. A dangerous and uncertain environment, on the other hand, will trigger the fast life, involving earlier reproduction, higher mating effort, and less parental investment. According to evolutionary logic (a strictly genes-eye perspective), if a girl's father doesn't invest in her care, then maybe other males will act just the same and therefore it is evolutionarily adaptive to not count on men as long-term providers and instead employ a short-term mating strategy.
The Dynamic Interplay Between Nature and Nurture
The complex, dynamic interplay between nature and nurture is mutually reinforcing. People's genes, which are partially shared with their parents, may influence to a certain extent what aspects of the environment they engage in, and those environments can in turn trigger and reinforce the expression of those genes. This can be unfortunate in situations where, for example, the genes that predispose someone to living the fast life causes that person to take dangerous risks that make his or her environment even more dangerous, causing a dangerous cycle. Therefore, when looking at the development of life history strategy, neither the environment nor genetic makeup can be viewed in total isolation from each other.
For instance, if the father's absence is due to accidental death, and therefore his absence doesn't reflect common genes between father and daughter, the daughter's chances of living the fast life are much lower than if the father's absence is due do divorce or abandonment (Khron & Bogan, 2001). In other research, Comings et al. (2002) found that a variant X-linked androgen receptor gene tends to predispose both fathers to absence from their children and daughters to living the fast life (but see Jorn et al., 2004 where this finding wasn't replicated). The effects of early environment must take into account the influence of genes in common between the child and parent
Fascinating epigenetic research looking at genotype-by-environment (GxE) interactions also suggest that not all people are equally influenced by environmental conditions. Some girls and boys are more reactive to stressful early environments than others because they are biologically prepared to be reactive to such environmental triggers. Infants and toddlers with a highly reactive and negatively emotional temperament tend to be more affected by parenting than other children, as do children carrying a particular dopamine receptor D4 allelle or alleles associated with low MAOA activity (Bradley & Corwyn, 2008; Bakermans-Kraneburg & Van IJzendoorn, 2006; Caspi et al., 2002). Nurturing and supportive family environments seem to have more of a positive effect on these children, and they also seem to be more negatively affected by harsh and unsupportive environments. In a very recent study, Barry, Kochanska and Philibert (in press) looked at attachment security in infants and found that infants with one or two short alleles on the serotonin transporter gene (5-HTT) were, unsurprisingly, affected by maternal sensitivity (low sensitivity led to attachment insecurity), but interestingly virtually all those carrying two long alleles became securely attached irrespective of the quality of care experienced.
Revisions of Belsky et al.'s (1991) and Chisholm's (1993) models acknowledge these important genetic effects by putting genes back into the picture. Belsky (2005) argues that while an early unpredictable family environment may have an effect on the development of an individual's life history strategy, not all daughters are equally prone to the fast life after living in unpredictable home environments. This certainly doesn't mean though that all people can't use a wide range of cues to adjust their life history strategy.
The mutually reenforcing pattern of nature and nurture assures that neither the genes nor the environment alone are destiny (see Straight Talk about Twin Studies, Genes, and Parenting: What Makes Us Who We Are). Just because your life history strategy at a certain age is rather stable does not mean you can't change your strategy (if you so desire); life history strategies are extremely plastic and highly sensitive to environmental triggers (although this doesn't mean change is necessarily going to be easy). Change the triggers, and you increase the chances that you will change the pattern of gene activations. Evolution "designed" humans to be highly sensitive to environmental cues and built in a great deal of plasticity into the human genome. Such plasticity would be more adaptive than rigidly "hard-wiring" at birth a person's life history strategy or allowing the environment to exert complete control. As Figueredo and colleagues (2005) explain,
"Natural and sexual selection would presumably favor enough developmental plasticity in the control of Life History Strategy to respond to an array of adaptive contingencies that were reliably present in human evolutionary history. Our results are consistent with this assertion, indicating that a substantial portion of the variation in life history traits remains under environmental control."
Also, these are all imperfect correlations. Not everyone with the fast life genes who are raised in harsh and unpredictable environments will start living the fast lifestyle. And not everyone living the fast lifestyle necessarily has the fast life genes or even were raised under harsh and unpredictable conditions. We are only talking probabilities.
The seductive allure of the fast life
Prior research had demonstrated a link between early environment and life history traits. For instance, there is research showing a link between a youths' exposure to violence and their chances of cigarette smoking
(Fick & Thomas, 1995), a link between the age of first sexual intercourse in adolescence and growing up in a low socioeconomic neighborhood (Browning et al., 2005), and a relation between maternal stress and distress and life history strategy development in boys (Barry, Dunlap, Cotten, & Lochman, 2005).
The life history strategy perspective, however, places these findings in a solid evolutionary framework and delineates the specific conditions that increase the probability of living the fast life. It's not just general stress in the neighborhood or just any aspect of the home environment that influences how a person's life history strategy develops, but particularly an interaction of a person's genes with an unpredictable environment high in mortality risks that primarily influences whether he or she, by their mid 20's, is likely to develop a fast or slower life history.
The fact that such a wide array of behaviors are linked together, are substantially under genetic control, and can be activated by particular life circumstances screams in high, Rock N' Roll fidelity, for an evolutionary explanation (see Part I, Evolution of the Fast Life). Life History Theory, derived from evolutionary principles, provides just that explanation and predicts that "family structure, sexual behavior, social behavior, and personality will be interrelated to produce an overarching life history strategy." For those with a specific constellation of genes living under harsh and unpredictable environmental conditions, the fast life may be particularly alluring.
© 2010 by Scott Barry Kaufman
Other Parts of the Series
Part I, Evolution of the Fast Life
Part III, Romantic Attachment in the Fast Lane
Part IV, Rebelliousness, Risk, Social Deviance, and Educational Intervention
Part V, Social Class and Public Policy
Part VI: Consilience, Pop Culture, and Modern Living
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