Lecture 9 - Life history & parental care Flashcards
What is the life history of humans?
Juvenile - 15+ (growing and learning)
Reproductive - 25 years (energy spent on reproducing, parenting, one offspring every few years)
Post-reproductive - 30+ years (grandparenting) extremely long, only humans really experience this and is unique to us - most animals reproduce and then die
What occurs during the post reproductive phase?
Senescence - when you’re older the body starts to fall apart, processes start to fail, cells start to die, slow process
What is the disposable soma (body) hypothesis?
Because of extrinsic mortality, individuals are not around forever
Evolution favours a higher number of offspring
Therefore energy is a limited resource
ageing and spontaneous death arise from the accumulation of damage
What is the extrinsic mortality risk?
the probability of an individual dying in a given time period through events in the environment that they could do essentially nothing about, such as predators, fluctuations in the food supply,
accidents, weather fluctuations, and so on
What is intrinsic mortality?
the mortality due to the organism’s own ageing
What does extrinsic mortality play a crucial role in?
whether a species should allocate energy to reproduction early or later on, and determines whether they live a short or long life
When is meant by the ‘trade-off’ between reproduction and self-repair?
Doing more of one means doing less of the other - the organism with the highest reproductive rate would be the one allocated all its energy to reproduction and none to self repair whilst that which repaired itself best would be the one that
allocated all its energy to repair and none to reproduction.
Do all organisms have the same life histories?
- usually body size associated with life history - larger body = slower life history. there are exceptions:
bats - slow life history - lifestyle allows them to escape predation that would affect them on the ground - live slowly for a long time.
African elephant - slow - not maturing until it is 15 years and having one
calf which suckles for nearly 3 years
bank voles (rat) - mature in a month and have 5 pups per litter
How is human life history considered slow?
Humans mature late (~15 years), have long gestation (9 months), small litter size (1), and relatively low extrinsic mortality—leading to long lifespans and late reproduction.
How is human reproduction different from chimpanzees?
Humans have higher birth rates (every 3.5 years vs. 5) and longer child dependence, made possible by cooperative care from fathers, grandparents, and others.
What is a pygmy population?
adult male heights less than 5ft tall
populations in Africa, Malaysia, Thailand, New Guinea, Brazil, and Bolivia
- life history theory suggests they might have a fast life history as an adaption to high rates of mortality as they live in high disease environments.
What is phenotypic plasticity?
the evolved capacity of the phenotype to alter its development in response to
cues during development that the world is in one state or another
What evidence supports the idea that humans adapt their life histories to harsh environments?
Wilson & Daly (1997) found that in Chicago neighborhoods with low life expectancy (due to high rates of homicide and accidents), women had more children and began reproducing earlier—often before age 25. This suggests humans may have evolved phenotypic plasticity to speed up reproduction in response to high mortality risks.
Outline evidence for how early life stress can induce changes in life history strategy
Pesonen et al. (2008) found that Finnish children separated from their parents during WWII showed faster life history traits in adulthood. Women had earlier menstruation and more children, while men became parents earlier and had shorter gaps between children—suggesting early stress may accelerate reproductive timing.
What is the optimal number of offspring to have at one time? (in birds)
5
Called the Lack curve - too many causes food scarcity and costs, could lead to poorer survival, mortality rates increase
What is the evidence for optimal clutch size theory?
By manipulating brood sizes, Daan et al found that while chick survival was only slightly lower in enlarged clutches, parent survival dropped significantly. Parents with reduced clutches survived better, showing kestrels limit clutch size to balance offspring care with their own survival.
What is different about the life history of twins?
They have higher mortality rates, less chance of survival
Explain how Sear’s study supports human brood size being subject to natural selection
Sear et al. (2001) showed that only 17% of twins survived to the age of 15 years, compared with 47% of singletons.
They also estimated that the rate of maternal mortality for twin mothers was
two or three times that of mothers of singletons.
What is the main quality-quantity trade-off for organisms whose young disperse soon after birth?
how many offspring to have in a single reproductive event
What is the evidence from Helle regarding the trade-off between quality and quantity in the human case?
Helle (2008) showed that every additional sibling reduced a person’s adult height by nearly half a centimetre, suggesting reduced access to resources.
What is the Trivers-Willard hypothesis?
the hypothesis that, when conditions are favourable (meaning basically that the mother is in excellent physical condition due to an abundance of resources), females of a species might be expected to preferentially give birth to sons, but when conditions are unfavourable, females of a species might be expected to preferentially give birth to daughters.
Evidence of the Trivers-Willard hypothesis in red deer
Clutton-Brock et al : Female deer can be assigned a dominance rank based on their ability to displace other herd members from resources.
Dominance is a behavioural measure, but it
correlates with physiological condition, with more dominant females having better body condition and calf survival. The researchers first established that the conditions for the Trivers–Willard hypothesis was met, that is, sons of high-ranking females had higher lifetime reproductive success than daughters of high-ranking females, but daughters of low-ranking females did better than sons of low-ranking females.
What is the evidence for maternal nutritional status benefiting reproductive success?
Gibson + Mace - in a rural ethiopian population, women with the lowest arm muscle mass have many more daughters than sons, whilst women with the highest muscle mass have more sons than daughters.
Dilemma: How much care should a parent give?
Taking care of an offspring for a long time is costly, i.e. energy and at some point, when you are older there is no point in giving care as they won’t learn anything new
Becomes costly when do it for too long
