BIO 115

1- an acute inflammatory response to select embryos with a potential of surviving (right after ovulation)
2- a profound anti-inflammatory response to enable implantation
3- acute inflammation leading to menstruation (elimination of bad embryos)

nutritionally and reproductively, But evolved to get rid of abnormal embryos
• But worth it due to the costs of human (and primates) reproduction

Our Post Reproductive span can be Longer than our Reproductive span

- 30 years and reproductive 25 years (Schätzung)

• Menopause may result from medically increasing the lifespan of a primate that is born with a fixed total number of gametes.
• But Menopause happens in humans even in societies that do not have access to modern medicine

• It is the result of a mismatch between the rates of reproductive and somatic senescence.
• Girls are born with an initial ovarian reserve of several hundred thousand primordial follicles.
• By age 40 around 3% of the maximum reserve remains.

longer / earlier

45-55 years (varies by more than 10 years)

whales (killer whales • pilot whales • Narwhals • Belugas)

Adaptation to increase fertility (QUANTITY) - one assumption for menopause
1- Mothers had to reduce IBI
2- Continue investing in QUALITY
3- Grandmothers had important role in increasing mother’s fertility

This leads to selection for Healthier grandmothers who are able to feed the grandchildren while mother invest in the next reproduction

fertility (7/8 babies) and shorter lactation period (2.6 years), ibi = 3.7 years

ADVANTAGE OF REPRODUCTIVE HELP (and possibly menopause):

• we adapted in a way to invest both in QUALITY and in QUANTITY, comparatively with other APES (both slow and fast traits)

Long Gestations
Large and Fat Babies
Long term dependent children (secondary altriciality)
Low Mortality Rates

= HIGH INVESTMENT IN QUALITY

• High Fertility
• Shorter lactation period
• Earlier weaning
• Shorter Interbirth Intervals (IBI)

= high investment in quantity

1) Ensures investment in quality of offspring

2) Ensures investment in quality and quantity of offspring

BUT: changes in current reproductive patterns lead to maladaptation in western societies (not so adaptive)

- girls are going earlier through puberty than years before (1860 16J - 1960 13-14J, now around 10 J)

• endometrial cancer (high levels of estrogen, obesity) = Endometrium
• breast cancer (rapid ductual cell turnover, pregnancy, protective: nursing, dietary changes, physical exercise)
• ovarian cancer (obesity, protective: increased parity, decreased ovulatory frequency) = Eierstock

may have longer cycles, longer periods, and heavier bleeding than women without the disease

• menopausal symptoms are the result from the sudden decrease of very high lifetime estrogen levels to zero during post-menopause (a new situation in our evolution and history)
• women in developed countries experience early menarche, menopause late, few pregnancies, short periods of lactation and consequently low life time progesterone levels. (traditional societies, the opposite)
• menopausal symptoms may be the result of a mismatch between female reproductive physiology and recent living conditions

It matters with whom you interact and what the cost and benefit of the interaction is

r = relatedness between actor and recipient

b = net fitness benefit for recipient 

c = net fitness cost to the actor

(rb) benefit from helping somebody else, cost of helping somebody else

• We are slow life history animals with very long lifespans (expected for our body size)
• Menstruation is an important life history adaptation for embryo selection, in a species that have very high reproductive costs.
• Menopause is a Evolutionary Paradox, “grandmother hypothesis” offers an adaptive explanation for the evolution of menopause
• Grandmother hypothesis explains menopause and could also explain why we have short IBI and other life history traits.
• Reproductive mismatches, led to increased hormone exposure which could cause some diseases in western societies that are not present in hunter-gatherers

Measure of interaction probability

i) and ii) are forms of cooperation

i) actor and recipient benefit -> benefit

ii) actor does not benefit, recipient does -> altruism

iii) actor benefits, recipient does not -> selfish

iv) actor and recipient do not benefit -> spite

1g / 1400g - human have very large brains, Most variation in primate brain size is explained by body size differences

Grand-mother hypothesis: early menopause in humans -> refrain from own reproduction to help daughters to rear their offspring

- c > 0, b > 0, r >> 0 (high relatedness is necessary for altruism to be selected for)

• encephalisation quotient (EQ) = observed brain size divided by predicted brain size for that body size
• EQ = 3 means the species has a brain 3 times larger than predicted for its body size

- Humans: Cooperative agreements through common interests

- Group hunting lions -> everybody contributes -> everybody benefits

- c < 0, b > 0, r is low or zero

Primates are high encephalised (i.e. we have large brains relative to our body) - humans are the most encephalised species (EQ=6-7), platz 2 und 3: mammals and dolphins

- Infanticide in lions: when male overtakes a pack -> kills cubs from past leader -> triggers earlier onset of the oestrus cycle in females

- Stag fights: conflicts between males over access to females -> winner takes it all

- c < 0, b < 0, r = low

neocortex ratio

- Human warfare: both will experience negative fitness consequences

- c > 0, b < 0, r < 0 (Relatedness has to be negative to be selected for)

1) grey matter: neuronal cell bodies, dendrites local circuits and functional modules

2) white matter: bundles of axons across long distances - shortcuts connecting separate functional modules

Natural selection favours individuals that maximize their inclusive fitness

• bigger brains cause a problem, Result: ‘obstetrical dilemma’ in humans (encephalisation vs. pelvic adaptations for walking)
• packing/folding of grey matter as a trick: Result: convolution reduces amount of white matter required to connect functional modules

• Human brains are large
• Primate brains (and ape brains in special) were already large before humans
• high encephalisation and highly encephalised ancestors
• a lot of white matter
• Human brains are highly convoluted
• The human brain has a unique structure