Lecture 10 Flashcards
What is the life hsitory theory?
It seeks to explain behaviours in terms of evolution and life history but looking at an individuals reproductive values. It differs across species because it is affected by the environment
Discuss the reproductive value
We assume that organisms are adapted to maximise reproductive value, which can be partitioned into current and future reproduction. Current reproduction depends on fecundity (fertility, natural capability of producing offspring) and offspring survival. Future reproduction depends on the probability of survival.
Discuss trade-offs
Because resources are limited, organisms may have to make trade-offs between components. For exaple, growth vs reproduction, offspring quantity vs quality, and current vs future reproduction.
Why not reproduce straight away?
During the juvenile period individuals cannot reproduce. If they reproduce early, it may cost themselves in terms of survival, for example comepting for more food when you’re very small. Also, reproducing is extremely energy dependent and babies don’t have enough themselves to be pregnant! However if we never reproduce we will die and our genes will not be carried on at all, so the costs of reproducing will be worth it in the future for juveniles. As when you finish puberty, you stop growing and thus you can spend that energy on reproduction. Males sexually mature later in life than females, partly due to male competition as they won’t win in fights against larger males if they are small! For example, Kudu males mature at 6, but females at 1.5.
Discuss r and k selection
R is quanitity of quality, e.g. fish. K is quality over quantity, e.g. elephants.
R-selected species: maximise rate of population increase. High fecundity, small body, short generation time and early reproduction.
K-selected species: maximise survival and reproduction when population is at carrying capactiy.
r/k selection is RELATIVE = invertbrates are r selected over vertabrates, rodents are K selected compared to elephants and individuals within a species can be more or less r/k selected.
This is often conceptualised as fast or slow life history strategy.
Discuss sexual maturation in humans
Hypothalamic-pituitary-gonadal axis (HPG) leads to gonadarche (develops gonads at about 10-11 years old).
Hypothalamic-pituitary-adrenal axis (HPA) leads to adrenarche (once adrenal gland matures, sex hormones mature).
Girls with premature adrenarche are characterised by exaggertaed reactivity of the HPA axis.
What are the effects of father absense on life history theory
Negative outcomes of father absense been found be Draper and Harpending (1982), with early experience defining a trajectory to maximise fitness - effects are strongest when in 1st 5 years of life, and they adopted a fast life-history theory. However presense of step father excels sexual maturity.
Outcomes include: 4x higher risk of poverty, more liely to become pregnant as a teen, 2x greater risk of infant mortality.
Discuss timing of puberty
Ellis (2004) found the mean age of puberty is 12 in USA. But why not as early as possible? BEcause the smaller pelvic size, lesser ability to gain weight for foetal nourishment, lower birthweights and higher rates of perinatal complications. As wella s less time to gain parenting skills, education and resources.
Energetics theory:
- greater energy availability leads to accelerated puberty.
- in poor countries, higher social classes enter puberty earlier.
- age of menarche dropped from 17 to 13 in Europe from 1830-1960 (during wars).
- reversal of the modern western pattern.
- In mammals, restricting energy delays sexual maturation, but only under severe conditions.
Stress-suppression theory:
- Stress stops or delays puberty.
- Stress can suppress the HPG axis, theoretically delaying maturity.
- Animal evidence is mixed however - subordinate primates delay puberty, but isn’t being dominant just as stressful?
- In humans in Europe, Russia and Japan, the decrease in age of puberty reversed during WW2.
Parental investment theory:
- stress accelerates sexual maturity.
- father absence is associated with higher chance of early menarche (before 12) about 2-3 times more likely.
- average effect around 4-5 months
- but is the father absence effect just another form of stress?
Discuss teenage pregnancy
UK has the higest rates of teen pregnancy in Western Europe (USA is highest in the World). It is strongly associated with poverty.
The government aimed to reduce is and spent £107m, by increasing sexual education and contraceptive availability.
Also a strong association with absent father.
Teenage mothers are born smaller and are breastfed for less time.
Discuss sexual preferences and behaviour
Earlier menarche is associated with stronger preference for deeper male voices, as well as with earlier dating, kissing, intercourse and first birth. There is limited and inconsistent data on number of partners, sexual fidelity, sociosexuality and good genes/good parent preferences.
Father absense and therefore fast life history theory should predict preference for masculinity and short-term mating. And it does when fertile. However, warmth to father predicted masculinity preference too.
Low mate value should lead to preference for less sought after mates.
Discuss the environments effects on reproductive behaviour
Violdent crime and wealth is associated with earlier birth (Griskevisius et al., 2011). Reading about rising violent crime changed attitudes to having children early. Those who grew up poor wanted children earlier.
Disaster can be follwed by local fertility spikes (Cohan & Cole, 2002). Administering corticosterone to side-blotched lizards accelerates reproduction in fast strategies, but delays it in slow strategies.
Chipman & Morrision (2015) experimentally stressed women with ice water and asked questions about when they wanted a child and wanted to get married. They found those who were more stressed wanted a first child earlier and marriage earlier than control group.
Summarise life history theory
Life history theory predicts that people should alter their reproductive behaviour depending on their conditions, how angerous their environment is and the availability of mates. Some very strong support for this!
