Flashcards in 3. Variation and life history Deck (81)
evidence for childhood adversity causing huge implications
With implications for health… Nettle (2014) very representative of the population
If look at c-reactive protein (inflammatory response marker shows strain immune system is under) if take adults and code on indicators of childhood adversity as adults they have the greatest levels of CRP.
This is a long term cost as they are exerting energy on maintaining a high alert state of immunity and not on other things
Also if look at self-rated health those who had childhood adversity were dramatically more unhealthy in 20s and those who had less childhood adversity maintained better health into later life.
Its not that people who experience childhood adversity have a fast life-history theory that sucks away energy (although it does do this).
Childhood adversity effect on self rated health- is small but significant. BUT if you then add in age of first pregnancy (stressful childhood, early pregnancy- which just took it out of you) what we find is that childhood adversity does predict age of 1st pregnancy this does have an effect on health but not losing much variance by adding pregnancy.
So looks like its not about life history its about other things carrying that stress with you.
is it all r/K? ticklist of what we would expect versus found
Is is all r/K
Do those with childhood stress/ father absence show
Early puberty- yes
Early reproduction – yes
Larger completed family size – no
Less parental investment- maybe
what are caveats to the findings of LHT
o Much research doesn’t hold true for non-western populations
o All the research is correlational- elaborate regression models even are still correlational it is not experimental
o Is difficult to rule out the effect that genetic mediation has to play
study on genetic influence on menarche
o Twins study (Mz; 0.57, Dz:0.32 concordance rates)
o Genetic effects = 0.5, unshared environments= 0.43, shared environment= 0.07
o 7% of variance can be explained by factors that both twins share
o Really father absence/ presence has to be shared environment – can’t argue that one twin is witnessing more family stress
o This only explains a tiny effect of the overall variance
what is an issue with Rowe's study?
To what extent is father absence itself associated with genes that may also predict age of menarche and if these two things are part of a genetic cluster that make you more r you might be more likely to be father absent as a male and hit puberty as a female
study that tried to control for issues with Rowe's study
Tither & Ellis (2008) tried to control for this effect
o Older vs younger siblings
o 93 pairs from biologically intact families
o 68 pairs from biologically disrupted families
o Usually when older sister is closer to menarche so effect of parents cant effect of age of menarche.
o Younger sisters in disrupted families are reaching puberty on average about 3 months before the older sisters. As younger sisters experiencing the stress younger in life
what can be said overall about genetics
This does fit with the model that it is environment and not genetics- but 3 months difference is this a hugely vast amount of time would this make actual difference on people reproducing?
what experimental evidence is there for LHT
non-human research on plasticity
non-human research on telomeres
Nettle et al (2014)
o Induced adversity shortens teleomeres (bits at end of chromosomes that get worn away when chromosomes are being copied when no telomeres left then damage to genetic code- one theory of aging)
o Teleomeres in Starlings cross-fostered into different nests to be heavier (ADV) or smaller (DIS) than brood-males
o At 12 days old can measure telomere length
o Find that those at advantaged environment had sig longer telomeres at day 12 than those at the disadvantaged environment
o Experimentally induced stress seems to be associated with shortening the telomeres faster.
non-human experimental research on behavioral outcomes for LHT
Bateson et al., 2014- behavioural outcomes
o Take a group of chicks from one nest
o Some go into low competition environment some into high competition environment
o Then behavioural test looking at how long they are willing to wait for a reward
o Either the trial starts if you press a button straight away get one pellet but if wait for x number of seconds you might get 5 pellets- the question is how long do you have to make chicks wait for 5 pellets before they stop and just go for the one pellet
o The more willing to wait for better reward- delay discounting- understanding that what you get at the end of it is worth the time taken.
o What modulates willingness to wait for rewards- measure of impulsivity
o Body condition (weight) and telomere condition is predicting impulsivity- those who have gained less weight because of competition have shorter telomeres and are more impulsive
o Argues that the physical effects of being in the more difficult environment are directing learning to more impulsive behaviour.
how does the behavioral research about telomeres relate to human findings?
Jergensen et al (2014)
o Cortisol inhibits telomere repair in humans
Thus elevated cortisol means that you take genetic damage at an earlier point- in that sense telomeres are an interesting candidate mechanism for stress impact on later development. The more telomere damage you are taking, the more long term genetic damage you will acquire, the shorter predicted life-span and the quicker you need to start producing.
So does fit with somatic approach
studies in west that father absence linked to +offspring and quicker
• More pregnancies
o Berezckei & Csanaky (1996) but see miscarriage rates as this balanced it out
• But certainly associated with more teenaged pregnancies & earlier first birth
• Ellis et al (2003); Boothroyd et al (2013)
how does the ecology of first birth differ in non-western samples for females
Father absence due to divorce delays Ache women’s age at first birth (Waynforth 2002. Handbook of Father Involvement). Those who are father present more likely to have had child in teens- within earliest period of potential reproduction
In Ache father’s v important for daughter nutritional status- if don’t have dad about then will have lower fat %, bone density, muscle mass- not going to be ready to reproduce at earliest stage so father’s are important
how does the ecology of first birth differ in non-western samples for males
Waynforth, Hurtado and Hill, 1998
Father absence due to divorce also delays Mayan men’s age at first birth.
Years of father presence negatively predicts first birth
Father’s v important in brokering children’s marriage so no father less likely to have a match and thus less likely to have children
what did Sear and Coall find about non-WEIRD and WEIRD samples in their systematic review?
o In WEIRD – most of the time father absence accelerates age of first birth
o In non-WEIRD- if include all significant studies then no effect- in all studies pretty even split between accelerate and delays
o Non-WEIRD- although very varied collectively are a bit more representative of early human environments.
what could indicate that nutrition has a role on menarche?
Is important as have to consider energetic ratios on mortality e.g. populations who live in mountains as may have huge calorie intake but also need to expend a huge amount to live in mountains
Athletes are a good example of this – very healthy very high calorie intake
o Physical stress and female reproduction
o Minimum body fat required for menarche- women need more body fat than do men because need minimum fat to keep reproductive process
o Female athletes often have disrupted menarcheal function- because of low body fat even considering their calorie intake.
o Nutrition and nutritional stress is really important in human reproduction
evidence that puberty onset is very different in WEIRD than Non-WEIRD samples
Sear et al. (pre-print)- Cross-cultural evidence does not support universal acceleration of puberty in father-absent households.
what did Sear et al., pre-print find about girls?
WEIRD girls- 60% of studies show that father absence accelerates age of first birth and rest it is doing nothing
NON-WEIRD girls- 72% of time doing nothing and then remaining time it is split between accelerating and delaying
What is going on in the west does not bear any resemblance to what is going on in non-WEIRD countries
what did Sear et al., pre-print find about boys?
WEIRD- boys (only 7 studies)- 55% time it does nothing, rest is maybe accelerating maybe delay
Non-WEIRD boys (only 5 studies)- 2 studies no effect- 2 studies delay and 1 study showing acceleration
Hard to say what is going on with boys as so much less well studies
what can Sear et al.,'s pre print study tell us overall?
In terms of girls is very clear again that WEIRD samples are weird and we are seeing effects that we can not see with anything like the same simple clarity as when we try and look at non-weird samples where it seems that probably nothing going on but if there is can go either way.