ANTHP105 Exam 3

Life history

strategy organism uses to allocate its energy towards growth, maintenance, reproduction, raising offspring, and avoiding death.

LIfe history theory

hypotheses that explain variation in life history traits across species:

• organism’s life history traits are typically interrelated

• energy is limited and harvested from environment

• principle of allocation: energy can only be used for one purpose

• evolutionary perspective: natural selection favors optimal allocation patterns (trade-offs)

Human energy allocation model: total energy budget

Total energy budget = maintenance + production

Human energy allocation model: maintenance

Basal metabolism

Dietary thermogenesis

Immune activity

Physical activity

Thermoregulation

Human energy allocation model: production

Growth and maturation

Reproduction

Allocation rule

Energy budget is finite; it must be allocated across competing biological functions

3 fundamental trade-offs of optimal allocation (evolutionary perspective concept)

Current vs. future reproduction

Quantity vs quality of offspring

Mating vs parenting effort

Three influences of life history strategy

Energy availability

Extrinsic morbidity/mortality

Predictability of change

Infancy time range

birth → 2 y.o.; includes neonatal period

Childhood time range

2 y.o. → 7 y.o.

Juvenile time range

Girls: 7 → 10 y.o.

Boys: 7 → 12 y.o.

Adolescence time range

5-10 yrs after puberty starts

Adolescence characteristics

• Growth spurt

• Length of time btwn age at puberty and age at first birth: about 10 yrs

• growth pattern is quantitatively different in rate, amount, and duration

• Female fecundity tracks growth of pelvis

Human growth rate (height velocity) is at its fastest during which time range

childhood

Life history trade-offs consist of mostly

time and energy allocation

Life history strategies are…

adaptive; humans are social mammals

Compared to other primates, humans have longer/shorter gestation?

longer

compared to other primates, humans have earlier/later weaning?

earlier

compared to other primates, humans have slower/faster postnatal maturation?

slower; we have a childhood

compared to other primates, humans have older/younger age of first reproduction?

older; we have adolescence

compared to other primates, humans have shorter/longer interbirth interval?

shorter

compared to other primates, humans have shorter/longer post-reproductive period?

longer; females experience menopause

Total energy expenditure is the sum of

BMR + additional energy expenditure (physical activity, fighting illness, digesting food, etc.)

Organs utilizing Resting Metabolic rate

Brain, liver, intestines, kidneys, skeletal muscle, heart, adipose tissue

Which organ uses the most energy from RMR

Brain

How do humans adapt to high energy cost of brain metabolism?

• High quality diet (reduced bulk/rapid assimilation and more energy available)

• Reduced gut size (less energy goes to gut’s functions)

• Newborns are altricial(incapable of self mobility immediately afer birth); brains grow rapidly after birth

• Cooperative breeding and allomaternal care

Humans have a much higher/llower quality diet than expected for their body mass?

higher

Compared to other primate species, human infant brain growth is…

much faster

Compared to the newborn brain size of primates, the newborn brain size of humans grows into an adult brain that is

3.5 times larger (compared to 2.5 times)

Allometry

change in size of one biological measure w/ respect to another

Kleibers relationship

RMR = a(bodymass^b)

Human brains have a … brain size than expected, based on body mass

larger

Relationship btwn femur length and body mass

proportional/positive

Relationship btwn lifespan and body mass

proportional/positive

Evidence of childhood first appeared in which species?

homo habilis

Relative to other primates, human infants are born…

immature

Precocial species

the young are relatively mature and mobile immediately after birtth

Why are humans categorized as secondary altriciality?

long gestation period

large birth weight

Compared to the great apes, human infants experience weaning

earlier

Adrenarche

process of adrenal glands secreting low levels of adrenal androgens; functions tied to increasing body size before puberty

Gonadarche

process of sex steroids production; initiation of puberty

weaning

transition from breast milk to complementary foods

complementary foods

any food/drunk fed to infant in transition from exclusive breastfeeding

Allomothering

infant care handled by any member other than the mother

How does early weaning allow for more offspring production?

shorter interbirth (btwn births) interval

Biological signals in breast milk reflective of mother’s nutrition and environment

Leptin: hormone produced by adipose tissue

FGF21: protein regulating the metabolism

TGF-beta-2: protein regulating the immune system

Humans infants are born with more/same/less fat than other mammals?

more

Body fatness of infancy peak

4-9 months

Hypothesis 1 for baby fat

Human brain uses 60% of basal metabolism energy (fat) for fuel

First mammary secretion

colostrum: rich in antibodies + vitamins, low in sugar + fat

Hypothesis 2 for baby fat (metabolic bottleneck phase)

infants store fat to prepare for weaning; complementary foods introduce new microbes and babies use their fat as an energy source to fight infection.

Rate of fat gain drops post-weaning

Metabolic bottleneck

period of constrained energy intake and high energy demands

Relationship btwn sum of skinfold and % w/ diarrhea

proportional/direct

sum of skinfold

subscapular skinfold + triceps skinfold

Development patterns in non-human mammals

• Infant depends on mother’s milk

• Weaning coincides w/ first permanent molar → juvenile period; offspring consumes adult food and forages for itself

• juvenile ends w/ puberty

Co-operative breeding

childhood stage of reliance on the group for food (ex. school)

Childhood rate of growth is ___ over time

steady; 5-6 cm/yr

brain growth in childhood speed

rapid

End of childhood is characterized by…

growth spurt

• Beginning of juvenile period

• coincides w/ first permanent molar and adrenarche

Hypothesis 1 for childhood evolution

increase in number of human offspring by decreasing interbirth interval

• Shorter weaning + cooperative breeding of child → mother allocation of energy toward next pregnancy

• Energy cost of pregnancy (285kcal/day) is less than lactation (500 kcal/day)

Hypothesis 2 for childhood evolution

increases chances of offspring survival and future reproduction

• brain development and learning; brain uses most glucose in childhood

adolescence time range

females: 10-18

males: 12 - 21

adolescence characteristics

• growth spurt in height and weight

• development of secondary sex characteristics

• intense interest and practice in adult activities

• Ends w/…

  • cessation of skeletal growth

  • completion of dental development

  • sexual maturation

Hypothesis 1 for adolescence evolution

Time for apprenticeship increases chances of survival and reproduction

Hypothesis 2 for adolescence evolution

adolescent’s ability to provide food and care while not reproducing → shorter interbirth intervals and increases parents’ reproductive fitness

Role of sex and gender in LHT

• LHT developed by white, cisgender men

• did not consider biological sex or gender identity as a complex trait

• data produced in societies w/ strict imposement on gender binary

Human reproductive ecology

study of ecological and evolutionary factors’ influence on human reproduction; focus on reproductive endocrinology

fecundity

individuals potentia capacity for reproduction

fertility

individual’s actualized reproduction (# of offspring)

sex hormones characteristics

• reflect variation in fecundity

• are sensitive to environmental conditions

• are easy to measure

Human fertility rate in evolutionary ancestors is… to predict

hard

Ovarian follicles

found in ovaries; they secrete hormones and have potential to release an egg cell (ovum)

primordial follicles

dormant follicles that have yet to develop; grow btwn fetal development and birth

menarche

first menstrual bleeding

pathways for growing follicles

either ovulation or non-ovulatory cycle

menopause

cessation of menstrual periods; avg at 51 yrs old

four reproductive hormones

progesterone, luteinizing hormone, estradiol, follicular stimulating hormone

follicular phase

first phase: follicles are maturing

all hormones at low levels

Ovulation

second phase: follicle rupture releases an egg

LH and estradiol at peak, progesterone low; generally, all hormones are at increased levels

Luteal phase

third phase: follicle becomes corpus luteum, producing progesterone

2nd peak of estradiol, but much smaller

Estradiol

estrogen steroid hormone; major female sex hormone

associated w/ follicle size, egg quality, and endometrium thickness

Produced mostly in ovaries, also in adrenal glands, fat, liver, breasts, and brain

Progesterone

essential for maturation of endometrium for successful planting of fertilized egg

produced by corpus luteum in ovaries and adrenal glands

Variation in ovarian hormones exist across…

• populations: ex. US women have progesterone levels 65% higher than those in africa

• individuals in a population: ex. higher variation across women in rural poland

• Within individuals: ex. seasonal changes in diet and exercise

Factors influencing ovarian hormone levels

Genes

Fetal environment

Childhood environment

Adult environment

Adult conditions

• negative energy balance (more calories burned than consumed) due to reduced levels of ovarian hormones w/o disruption to menstrual patterns

• Frequent menstrual disturbances in women athletes

• Ovarian suppression as evolutionary adaptive phenomenon

Ovarian supression as an adaptive phenomenon

Due to high energy costs of pregnancy and lactation, ovarian function turned on/off based on energy balance.

Protects maternal condition and optimizes lifetime reproductive output

negative energy balance → reduced chances of conception

Theories of other factors influencing ovarian hormones

smaller waist-to-hip ratio → higher ovarian hormones

Psychosocial stress → infertility

CYP17 polymorphism (genetics)

What does CYP17 code for

aromatase: enzyme key for estrogen synthesis

High lifetime levels of ovarian hormones increase the risk of which cancers?

breast and ovarian

Oral contreceptives effects from women to women

varies due to differing natural hormone levels

Males primary allocate energy toward mating or parenting effort?

mating; producing offspring is very low energy cost for males

GnRH

Gonadotropin releasing hormone; pulsatile secretion begins during puberty from hypothalamus to pituitary glands

testosterone

primary male sex hormone produced by the testes

• plays role in physical development, aggressive behaviors, and libido

• insensitive to short term negative energy balance, but is lowered by long term fasting

• diurnal (24-hr cycle) rhythm

• declines with age

factors influencing variation in testosterone levels

• moment-to-moment, depending on GnRH

• Genetics

• acute psychosocial stress → lower testosterone

• infectious disease → lower testosterone

• competitive events

• age

the decrease in testosterone when fighting an infectious disease is an example of…

physiological mechanism of energy trade offs btwn maintenance and reproduction

fecundity by sex

females: tied to nutritional status

males: independent of nutritional status

Challenge hypothesis

observed spike in male bird's’ testosterone levels when competing with other males for mates; argues that testosterone spike increases behaviors needed for competition for mates

Relationship btwn mating effort and sexual dimorphism

species of males allocating more effort to mating exhibit greater sexual dimorphism

What do males depend on to allocate energy in mating vs indirect care for offspring?

environmental conditions

monogamous bonding + provisioning of female and offspring results in natural selection for

• increase in offspring survival

• decrease in interbirth interval

• sex-based division of labor