Lecture 16
Anth 160 , Spring 2001, Lecture, Slides
Humans share many
characters with other mammals in their growth and development.
Determinate growth, stop growing,
put everything into reprodution
However, humans have two very distinct adaptive characteritics which affect the way in which their life histories unfold , both closely linked to a major human adaptations.
1. Feeding of juveniles—humans underwrite the
period of growth during juvenility between weaning and reproduction. This means
that human females are uniquely burdened with provisioning both infants and
juveniles.
2. Large brain which mainly grows after birth
but before the age of 5.
Human development and reproductive biology modified to meet these two major forces in their life history.
Sexual dimorphism in
animals: what is it about.
Sexual dimorphism is
not a thing in itself that is selected for.
Males are not selected to be bigger than females, they are selected to
be as big as males need to be and females are selected to be as big a females
need to be. The difference between them
or the similarity is a measurement of two independently determined factors. But we talk about the relationship as if it
was an entity.
Weaponry:
Canines in many
mammals, sometimes horns, antlers.
Canines are a more primitive condition—deer started out with canines and
then lost them when antlers evolved (same with cattle).
Will there be sexual
dimorphism in canine length—it depends on what they are used for.
Not in predators like lions and black bears in
spite of big sexual dimorphism in body size in lions. Why? Canines are used for
hunting; females have to hunt for themselves and offspring, and in some places
for males too.
6. Black bear,
chacma baboon, African lion
7. Gibbon and chimp—no
sexual dimorphism in canines or body size for gibbons, why?
They
live in monogamous pairs, and both defend territory. Female grows to male standards because she defends her territory
and keeps rival females away so her mate won't be so foolish as to try to
support two females at once by inviting a second to share their territory.
8. Sexual
dimorphism in body size
Most
extreme in primates: only about 2:1
Orang male is 100% larger than female
(elephant seals are 6:1).
9. Sexual
dimorphism in apes and humans
Takes
different forms. Most apparent is body
size.
What
else? Pprimate's use genitals as
adverts.
Most
modest – Gorilla males have small penises, small testes close to the body, and
low rates of sex.
Females have minimal sexual swelling
and solicit sex by approaching male.
Most
spectacular – Chimpanzee males have long penis and very large testes.
Females
have sexual swelling—a brightly colored advertisement that can be seen 1.2
miles away.
Humans – Males have
large penis relative to body size, but not very large testes compared to
chimps.
Females
have no sexual swelling to advertise estrus or fertility which is something
new, and have
permanent
breasts. What is this about?
10. Sexy look
directed to one male
11. Female sexual
swelling in baboon
12. Gorilla breasts develop during last trimester of
gestation and are not permanent. They
are composed of tissue that produces milk and not of fat deposits.
13. Adolescent growth spurt in height—mean
velocities under good nutrition
14. Epiphysial
union.Cartilagenous plates
girls, estrogen
concentration fuses every bone in the body except one where is stimulates
growth. Which one? pubis, the only bone in the female body that
is absolutely larger than male’s
15. Pubertal sequence
short, boys and girls
Actual onset of
puberty, adrenarche and puberty at the same time, 8 and 10. What is different in boys and girls is the
timing of specific events in the sequence, growth spurt, mature sex cells
fertile
eunuch – males are fertile before developing adult appearance
infertile
tease – females develop adult appearance before becoming fertile
16. What are the
programs for boys: invest extra nutrition beyond maintenance to growth in
stature and muscle mass. Both are
expensive but worth it.
17. Secular trend,
height of English boys 1833-1958
Increase
in stature mean over time—reflects better nutrition as a whole, social
stratification, stunting of poor males.
Reaching of adult stature at an earlier age—18. Almost no males in our society grow more
than a trivial amount after 18 (those who do, like some basketball players,
become very tall). At end of
Pleistocene, very tall means of limited samples. Mesolithic and Neolithic means shorter in particular regions, in
Greece there is an appearance of really small peoples—pygmoids.
Recovery of adult male
stature of 5'8" after WWII
18. Height of males
and females US 1960's—why are women smaller, what are they doing with extra
energy?
19. Menarche—weight velocity precedes onset of
menarche (first menstrual period). Time
lapse occurs before regular ovulation and ability to implant - needs hormonal
sufficiency and balance for this, which takes about an additional 3-5 years.
20. Secular trend in
age of menarche, 1840-1970
Decreasing 3 months
per decade? Details are not important,
what is, is that most girls in 19th and early 20th century had
puberty at - 14-15-16, and probably became fertile immediately. Only daughters of privileged had puberty
early. Today, mean age of puberty is
12, which means that many girls reach puberty at 10 and 11. Practically all are fertile by 15. We know of some groups today that are very
late—New Guinea has a mean of 19 (probably due to low levels of protein).
21. Diagram of female
body fat—hips, thighs and buttocks—this is what they are doing with extra
energy.
22. Lower body fat
vs. upper body or trunk fat. Cells differ
in size, number, hormones of deposition and access – starvation.
23. Sexual dimorphism
in stature, weight, midtriceps fold, n = 527
24. Sexual dimorphism
of Michigan whites, ages 20-70
25. % females obese
in developed and underdeveloped countries.
Wild
primates have only about 5% body fat – humans are extremely fat!!
26. Female body
builder with 6% body fat (like a male runner).
28. Venus of Laussel,
France, end of Pleistocene
Oldest record of establishment of human
fat pattern for women—not like other primates.
29. Why store fat,
why so important to human reproduction?
Why should women store fat in special places and use estrogen and
prolactin to make deposits and withdrawals.
San
Breast feeding: long lactation
Female monkeys start breeding even
before reaching full adult body size—grow during first pregnancy and early
lactation
30. Weight gain in
pregnancy, allotment to fat, last trimester, no store, skinny baby. Maternal fat storage is more important than
having baby with fat reserves.
Brain
growth spurt in 7 species.
32. Growth of brain
for humans, chimps, and rhesus monkeys.
33. Neural tissue has special growth patterns and is not
like other cells.
Metabolic rates, 1-1
50 lbs., % of total BMR
The
infant brain is a very greedy organ, taking most of the nutrition of the child
between weights of birth and 50 lbs.
34. Daily cost of
pregnancy and lactation as % of mother’s body weight - minimal daily cost
but has to be paid every day for years.
35. Male
stature as a % of female stature—small range 104-110??
Females
stop investing in growth and divert all extra energy to the storage of fat.
OVERHEADS:
1) Life history trade-offs
2) Female
waist-to-hip ratio 1, 2
3) SUMMARY
