ANT208 Lecture 7 - Biosocial interactions and health similarities, tradeoffs in evolution of human life history and cooperative care

mortality

frequency of death in a population; mortality rates a key indicators of population health

longevity

length of time and individual lives

common measure of population health

Under-5 mortality rate - probability that a child born in a specific year or period will die before reaching the age of 5

• Poor nutrition

• disease exposure

• limited healthcare

When is the highest risk of death in humans and why

Early childhood (especially infancy); weak immune systems, dependence on caregivers, sensitivity to environment (nutrition, disease)

effect of early life mortality on human evolution

favors traits that protect and care for young children

• parental care

• alloparenting

• breastfeeding

why do humans invest heavily in childcare

survival though early life increases chances of reproduction

mortality risk in later life

increases again due to aging and biological decline

Why can’t older individuals reproduce

senescence and reproductive system decline (menopause)

maximum longevity

maximum lifespan a species can achieve under ideal conditions; all species have one

Overall human mortality pattern

• high mortality in early life

• lower risk in adulthood

• increased mortality again in old age

healthy aging

living longer with good health and minimal disease, not just surviving

longevity vs healthy aging

• L = length of life

• H = quality of life during those years

Why do humans live so long

• long childhood

• extended adulthood

• social cooperation

Long lifespan as a life history trait

refelcts evolved strategies balancing growth, reproduction, and survival

Life expectancy

average age at death in a population

Effect of early life on life expectancy

high infant and child mortality lowers average lifespan; if many children die young, life expectancy appear low - even if adults live long

factors increasing life expectancy

• good nutrition

• healthcare

• low disease burden

• stable social conditions (no war/conflict)

Factors decreasing life expectancy

• infectious disease

• malnutrition

• conflict/war

• poor living conditions

Life expectancy as a population health measure

reflects overall health, environment, and social conditions

Why is life expectancy partly a social measure

depends not just on biology

• healthcare systems

• inequality

• public health infrastructure

survival vs healthy aging

living longer does not mean living well

Evolution and aging

evolution favors survival until reproduction, not necessarily long-term health (ex. traits that help early survival may contribute to aging later (tradeoffs)

Key idea of human aging

humans are evolved to live long, but quality of life depends heavily on environment and society

Developmental Origins of Health and Disease (DOHAD)

idea that early life conditions shape the rise of disease in adulthood

Key Principle of DOHAD

early development (especially prenatal and early childhood) has long-term effects on health

Most important life stages for DOHaD (why

organs and systems are developing and highly sensitive to environmental influence

• prenatal (gestation)

• infancy

• early childhood

Early life exposures that affect adult health (metabolism)

• toxins (pollutions, pesticides)

• alcohol and drugs

• secondhand smoke

• poor nutrition

• lack of care and social support

Timing of exposure

damage during critical windows can have permanent effects

• brain development disrupted early → cognitive deficits

• immune system affected → higher disease risk

What adult diseases are linked to early-life conditions

• Cardiovascular Disease (CVD) - undernutrition

• diabetes - undernutrition

• asthma - modern environment

• mental health disorders

How do early conditions affect later disease risk

altering…

• metabolism

• organ development

• immune function

What is programming in DOHAD

early environments “program” the body’s systems, influencing how they function for life

DOHAD and Evolution

early life conditions prepare the body for the expected environment

• poor nutrition early → body adapts to scarcity

• if later environment is rich → mismatch → disease risk

Mismatch in DOHAD

early-life conditions do not match adult environment

• undernourished fetus → grows up in high-calorie environment → obesity/diabetes

biological fitness

ability to survive and reproduce relative to others

antagonistic pleiotropy

when a gene has benefits early in life but harmful effects later; evolution favors these genes because natural selection prioritizes early-life reproduction (ex. a gene that increases fertility but causes disease in old age)

Coevolution in humans

traits evolve together to reduce vulnerabilities

• ex. long childhood → supported by prenatal care and social cooperation

human life history dependent on social systems

survival depends on shared care, culture, and environment

two levels of explanation

• proximate

• ultimate

Proximate explanation

the immediate, biological mechanism behind a trait or condition

• ex. Anemia

  • low hemoglobin → reduced O2 transport

Ultimate explanation

evolutionary or environmental reason a trait exists

• ex. Anemia

  • sickle cell trait evolved in malaria environments

  • diet, ecology, and stress influence prevalence

Adaptive hypothesis to explain traits

a trait exists because it increases fitness (survival + reproduction) through natural selection - WHY it exists

Why is it hard to prove adaptation in humans

• long generation times

• difficult to observe directly - ex. traits that improve survival in specific environments

Phylogentic Hypothesis to explain traits

traits exist due to evolutionary history and may persist even though they are no longer being elected through natural selection (ex, vestigial traits/organs) - HOW it works

appendix

• adaptive explanation: no selective pressure for it to be dropped, retained because it does not have effects

  • historically thought to be vestigial

  • may have minor immune functions

Why do whales have vestigial leg bones

Phylogenetic explanation: an ancestral trait due to phylogenetic history of having terrestrial mammal ancestors

• remnants from terrestrial ancestors

• no longer functional in aquatic life

proximate explanation of aging

explains how aging happens biologically (mechanisms inside the body)

is aging biologically programmed

yes, partly - aging reflect biological processes shaped by evolution and trade-offs

Why isn’t the body designed to live forever

life history tradeoffs

• energy is prioritized for growth and reproduction not indefinite maintenance

Mid-life has lowest mortality

natural selection favors survival until reproduction is complete

death is more common in old age

selection pressure weakeneaps after reproduction → aging effects accumulate

people age differently

genetic differences and environmental exposures across life

• diet and nutrition

• disease exposure

• stress levels

• lifestyle (exercise, smoking)

Expectations about aging change over time

they are shaped by social and environmental conditions (today, a 70 year old may be active but 100 years ago, that would be unlikely)

Aging has changed in modern societies

• better healthcare

• improved nutrition

• reduced infectious disease

key idea about proximate aging

aging is the result of biological process and lifetime exposures, shaped by evolutionary tradeoffs

age- related changes

gradual declines in functional capacity across body systems with age

which body systems decline first

1. lung capacity

2. muscle strength

3. kidney function

4. heart (max heart rate)

5. brain (declines slowest)

BMR and age

BMR declines with age

Do all body systems decline at the same rate

no, each system declines at different speeds

Slowest system to decline

because they are essential for survival, they are better maintained

• heart

• brain

• kidneys

Infection and Aging

aging increases severity and recovery of disease, not necessarily incidence

when do chronic illnesses typically increase

around 45+ (especially in industrialized societies)

common conditions with age (similar for males and females)

• arthritis

• cataracts

• hearing loss

• heart disease

• hypertension

female gonadal decline

• declines earlier and faster than other systems

• ends with menopause

male gonadal decline

remains relatively high until ~ 70, then declines more rapidly; slower than many other systems

factors that accelerate function decline with aging

• poor diet

• lack of exercise

• social inequality (lower socioeconomic status → earlier onset of chronic disease)

• chronic stress

Is “normal aging” purely biological

no - also shaped by social values and expectations

How we define healthy aging

• culture

• healthcare access

• economic resources

• social priorities

Key idea about aging and function

aging involves gradual, uneven decline across systems, influenced by biology, environment, and society

Has maximum human lifespan changed

no - still about 120 years

Average lifespan is increasing globally

• lower infant/child mortality

• reduced infectious diseases

• improved healthcare

Senescene trend in some countries

a larger proportion of life spent in senescence (declining function) - ex. people live longer but may spend more time with chronic illness

Social roles of older adults vary across cultures

• culture

• gender

• social values

• economic systemsM

Menopause a “contested concept”

can be defined:

• biologically - end of reproduction

• socially - change in role/status

How are older individuals socially categorized

• othering

• stigmatization - women often experience stronger age-related stigma

• ageism

“sick role” in aging

expectation that older people are frail, dependent, and vulnerable; changing as there is more focus on “healthy aging” and active lifestyles

cognitive aging is an increasing concern

more people living longer → more cases of dementias

social and economic impacts of cognitive decline

• increased healthcare costs and demand

• greater caregiving needs

• vulnerability (scams)

• economic planning

• pension systems

• political influence

medicalization of aging

treating normal aging as a medical problem

“greying of populations”

increasing promotions of older individuals in society

family structures changing aging

• more people live alone

• less family-based carehatw

what replaces family care

• social services

• assisted living technologies - retirement homes, homeware systems

general biological pattern for lifespan

larger organisms tend to live longer - exception is birds who tend to live longer than expected for their size

Thrift genotype hypothesis

• efficient fat storage helps survival in scarcity (early benefit)

• leads to obesity/diabetes in modern environments(late cost)

Disposable some theory

the idea that the body has limited energy that must be divided between

• maintenance/repar (soma)

• reproduction

what happens after reproduction begins

energy is increasingly allocated to reproduction over repair, leading to aging

• less cellular repair → accumulation of damage → senescence

caloric restriction and aging

• reduce free radicals (cell damage)

• increase antioxidant activity

  • potentially slows aging and leads to longer lifespan

factors influencing lifespan across cultures

• diet

• environment

• lifestyle

• energy allocation

what explains overall human senescence

• evolutionary trade-offs

• energy allocation decisions

• environmental influences