HSCI 216 Lecture Notes - Lecture 3: Coevolution, Leg Before Wicket, Body Composition

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HSCI 216
DAY 3
May 25, 17
Human Life History Theory
Human life history learning objectives
- To state what is life theory’s main postulate
- To describe overall fitness and the principle of allocation
- To describe the unique characteristics of human life history
- To compare and contrast human growth patterns from other less-social mammals
- To discuss the purpose of human adolescence and why the purpose is sex-specific -
EXAM
- To discuss main reproductive trade offs faced by women
- To describe the hypotheses developed to explain senescence and menopause
Life History Theory (LHT)
- Postulates that ontogeny has been shaped by natural selection
- Organisms (in average) are expected to follow resource allocation patterns across their
life span that result in an optimization of their overall biological fitness
- Ontogeny: origin and development from moment of conception
- overall biological fitness: individual fitness and inclusive fitness
- Individual fitness: offspring produced by self
- Inclusive fitness: “positive” effect on the fitness of relative
Some (extreme??) examples of individual fitness
- Moulay Ismaïl Ibn Sharif fathered 850 children
- Genghis Khan 10 acknowledged children could be way more raped women
Inclusive fitness
- To calculate if a behaviour will have a positive selective value Hamilton developed the
following mathematic equation:
rb > c
- C = reproductive cost to self energetic wise
- B = reproductive benefit to the recipient
- R = coefficient of relatedness
- No inbreding
- The problem is usually in estimating the reproductive cost and benefits
Have you ever heard of “nepotism”
- Why does nepotism exist?
o Help increase your overall fitness, its going to evolve
- Why do people tend to favour relatives?
So how do individuals maximize fitness?
By optimizing resource allocation throughout
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Resource allocation is key to understanding Human Life Theory
Basic HLT:
- Principle of allocation: (at any given life stage) energy used for the one purpose cannot
be used for another
Where and when to invest energy?
- Natural selection is expected to favor the evolution of optimal allocation
What do we need to allocate energy to?
- Growth
- Maintenance
- Reproduction very energetically costly more for 1 sex than the other
When and where should we invest energy?
Growth vs maintenance vs reproduction
- Optimal allocation implies trade-offs
- Do children invest in reproduction?
o Did you take care of your younger sibling growing up? yes
An Overview of Human Life Stages
- There are 5 main stages in human life:
o “pre” stage: prenatal stage
divided into 3 trimesters
1st: Fertilization to 12 weeks (embryogenesis)
2nd: 4th-6th month (rapid growth in length of fetus)
3rd: 7th month to birth (rapid growth in weight and organ maturation
o Postnatal
Childhood
Infancy: birth to 3 years
Juvenile: Girl 7-10 years / Boys 7-12 years
o Adolescence: 5-10 years after puberty
o Reproductive life: ~ 18 years old to end of child bearing
o Post reproductive life (senescence)
Menopause = andropause
- Why do humans go thorugh these stages?
- How do these stages relate to health?
Human life history in perspective
The mammalian pattern
- Most non-social mammals are weaned directly into independent foraging and feeding.
Humans and other social mammal continue to be highly dependent on others for food and
protection, post weaning. Why?
- Early human diet is quite particular as the digestive system is slow to mature (teeth
eruption, digestive enzymes, etc.) and the energy demands are substantial why?
- For most mammals the progress from infancy to adulthood is seamless, without
intervening states. Puberty occurs quickly after postnatal growth peak (~ 25 days)
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- In humans, growth continues slowly for a long time after infancy, puberty and even after
sexual maturation. Why?
What is special about human childhood?
- Relatively small body size
- Slow and steady rate and growth
- Dependent feeding (immature dentition)
- A large, expensive, fast-growth brain (87% of newborns’ RMR dedicated to it! Twice
that of chimps)
- Higher RMR than any other mammalian species (pick up baby, baby super warm because
of fast metabolic rate)
- Motor and cognitive immaturity
- Adrenarche (shared with chimps) and mid-growth spurt (unique to humans)
What differentiates us from other apes?
- In humans there are delays in:
o Eruption of the first permanent molar
o Menarche period is delayed in humans
o First birth
- Despite a slower LH schedule… humans have shorter birth intervals
- Short IBIs humans are an advantage over other apes, because we can produce and rear 2
offspring through infancy in the time it takes chimps or orangutans
Social Mammals!
Other people can feed the child
Reduction of period of lactation
Reduction of interbirth interval
Greater life time fertility for the mom
What explains human childhood?
More time for developmental plasticity
More precise tracking of ecological conditions
Greater offspring survival rate (biggest goal is to survive)
Greater life time fertility for the offspring
iClicker questions
1. From an evolutionary point of view, which of the following wil influence your overall
fitness
a. the number of surviving offspring you produce
b. the number of surviving offspring your relative produce
c. community produces
d. a and b answer
2. the principle of allocation (part of life history theory) applies to:
a. metabolic energy
b. time
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Document Summary

To state what is life theory"s main postulate. To describe overall fitness and the principle of allocation. To describe the unique characteristics of human life history. To compare and contrast human growth patterns from other less-social mammals. To discuss the purpose of human adolescence and why the purpose is sex-specific - To discuss main reproductive trade offs faced by women. To describe the hypotheses developed to explain senescence and menopause. Postulates that ontogeny has been shaped by natural selection. Organisms (in average) are expected to follow resource allocation patterns across their life span that result in an optimization of their overall biological fitness. Ontogeny: origin and development from moment of conception. Overall biological fitness: individual fitness and inclusive fitness. Inclusive fitness: positive effect on the fitness of relative. Moulay isma l ibn sharif fathered 850 children. Genghis khan 10 acknowledged children could be way more raped women.

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