BISC 102 Lecture Notes - Lecture 21: Sperm Competition, Sooners, Homo Habilis

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November 12th, 2015
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What are we doing today?
sexual selection: quick review
mate choice
what women want
does it increase their reproductive success?
what men want
does it increase their reproductive success?
human mating systems
Homo Habilis - The Handy Man
2.4-1.6 mya
short jaw and small molars
larger brain (600-750 cc)
tool use
this is the first species associated with tool use
Tool Use
appears more than 2 mya
H. habilis and/or A. garhi (450cc)
shift in diet?
shift to more soft materials (meat)
tools and meat eating would have gone hand in
tools allow you to kill more easily
evidence of cognition
the first fossil beds where we found these tools there
are fossils of A. garhi and H. habilis and we aren’t sure
which species or perhaps both used the tools
Homo ergaster - The Working man
1.9 to 1.5 mya
long slender legs
very efficient at long distance walking
small teeth
particularly smaller molars
larger brain (900cc)
jump in brain size
reduced sexual dimorphism
males and females are just about the same
size (or males are a little bigger) shift away
from polygyny to monogamy or a more
promiscuous mating system
African species
Homo erectus - The erect man
1.8 mya to 190,000 ya
out of Africa to Asia
first hominin to leave Africa
colonized large parts of Asia
Homo neaderthaensis
200,000 to 25,000 ya
Europe and the Near East
first european species
the african species were slender and long
neanderthals were stalkier and shorter
large brain (1200-1700cc)
brain size comparable to our own
did neanderthals and humans interbreed?
in Europe sapiens and neanderthals coexisted
in Europe for 25,000 years
in the last 2 years the neanderthals genome
has been sequenced
Homo sapiens
oldest fossils 195,000 ya from Ethiopia (African
migrated out of Africa - 115,000 ya
colonized every other part of the world
derived characters (mostly mental/behavioural)
lost the heavy brow ridge that characterized the
earlier hominin species
abstract thought
cave paintings
being able to represent something that
is not actually there
specialization and diversification of
a tool for a specific purpose
early rituals (burials)
making things that aren’t purely
goal-directed behaviour
the ability to explore and to expand
to live in areas that are inhospitable
creating trade networks, planning trips
1.6% dierence in 5-7 million years (between
genomes of chimpanzees and humans)
Homo naledi
new species of human ancestor discovered in
South Africa
Human Behaviour
Sexual Selection: process by which individuals that
have traits that increase their mating success are
favoured over individuals that do not have these
1. Competition - mate as much as possible
(mainly in males)
2. Mate Choice - mate as carefully as possible
(mainly by females)
How to study mate choice in Humans?
Belle Sorenson Gunness
we expect females to want partners that are
going to increase their reproductive success
we expect females to be choosy
in the 19th century people were using personal
ads to find partners (didn’t last long)
Gunness was accused of killing 28 men
by attracting them via personal ads
Female Mate Choice
Advantages of
Personal Ads
Disadvantages of
Personal Ads
not aimed at
short so only
important info
advertisers are
truly interested (
motivation is
people might
understate what
they truly want
people might
overstate what
they have to
parsimony - includes things like reliable, integrity,
Female mate choice...
Words to Avoid Words to Use
1. vegetarian
2. lonely
3. retired
4. divorced
5. married
6. short
7. frugral
8. overweight
9. like fishing
1. loving
2. reliable
3. monogamous
4. caring
5. career-oriented
6. romantic
7. honest
8. unattached
9. marriage
= Commitment and
Who can provide resources?
1. Older Men
they have had more time to accumulate
or their parents died and they inherited
2. Intelligent Men
get good jobs, garner resources
as commitment level increases so does
the requirement of an intelligence level
(for women)
When Women cannot get resources (or don’t want
when they don’t want resrouces from the
partner women go for good genes
Do mate presences increase female RS?
characteristics that women are looking
for do contribute to their reproductive
success if they manage to find a mate
with these characteristics
Does wealth still correlate with RS?
Male-Male Competition
males do compete
men have more violent manifestations of
competition when their reproductive success
is challenged
Rates of Infidelity
USA (Kinney
UK (Johnson
Female 26% 10%
Male 50% 20%
Sperm Competition
mate guarding: strategies to reduce the
potential for sperm competition
Should males ever be choosy?
Yes, if they invest a lot into ospring
high investment means it is more important to
choose the right mate
in general human males do invest a lot
in their ospring - we do expect them to
be choosy
Male Mate Choice
Tips to get a good mate...
Words to Use (if you’re
a woman)
Words to Use (if you’re
a man)
1. good figure
2. attractive
3. trim
4. sexy
5. sharp dresser
6. good-looing
7. young
= Looks
1. loving
2. reliable
3. monogamous
4. caring
5. career-oriented
6. romantic
7. honest
8. unattached
9. marriage
= Commitment and
Who can provide ‘looks’?
1. Young women
2. Intelligent Women (sort of)
3. Shapely women
1. some fat
2. low waist to hip ratio
Do mate preferences increase male RS?
Eect of age on female fertility
women peak in fertility in their early to
mid twenties
men who marry young women tend to
have more fertile partners
Eect of fat on female fertility
fatter women...
reach puberty sooners
gain more weight during
have fatter babies that grow fatter
fetter babies survive better under
nutritional stress
Eect of low waist-to-hip ratios
low WTH ratios indicate...
general health
pregnancy state
Human Mating systems
in terms of number of people - most people
monogamy is most prevalent
this is not what the statistics show
the majority of human societies have a
polygynous mating system
this is not what we expect from strong mate
Paternal discrepancy in ‘monogamous’ societies
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