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Lecture 8

ANT208 Lecture 8

10 Pages
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Department
Anthropology
Course Code
ANT208H1
Professor
Dan Sellen

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Ant 208: reproduction part 2
sex determination + sex differences
o relate what we know about human sex differences to the evolutionary selective forces
that produce these differences
reproductive strategies
o look at the differences in life history strategies that emerge from different gamete sizes
o sexual selection: mate choice and parenting
drives a lot of the differences we see between genders in the living world
o sex differences: development and life history
o ecological variation: secular changes
there are changes across context based on the cues that individual bodies
receive from their environments
there are also changes over time (secular changes)
reproductive health, bia gender
o birthing, breastfeeding
o sexual health
many concepts are constructed currently in biomedicine, and raise the question
that some conditions that are currently characterized as sexual dysfunctions
may actually be side-effects of environmental mismatch, or they may be simply,
culture bound misinterpretations of biologically very normal things.
Sex determination
biological sex and gender = function of phenotype
product of genetic and environment -> single informational unit
Ordered process
o Chromosomal sex (fertilization)
XX, or XY?
o Gonadal sex (early fetal development)
In the first six weeks: the emergence of gonadal sex
Either the default production of female gonadal sex tissures, or in the presence
of testes determining factor, the development of a different type of gonad
(male gonads)
o Phenotypic sex (accessory sex structures)
Determined after puberty
Chromosomal sex usually agrees with phenotypic sex (but not always!!)
“epigenetic” influences
o All sorts of environmental exposures can modulate gene expression during the lifespan
o Modulate gene expression during lifespan
o Early development has long-term effects, larger influence
o Age, education, experience, conditioning
Explaining sex differences
Generalized differences between male and female
o Bodies
o Health risk and vulnerabilities
Great interest in the past 25 years in global policy, public health, and feminist
approaches to addressing gender inequities in health
Health risks are also a product between evolved vulnerabilities and social
contexts
o … support predictions of evolutionary theory
These changes are what are expected in an evolved biological context
Sexual selection theory
o Predicts that there would have been many species, an evolutionary history of gender-
specific selective forces
o Gender-specific lifetime investment in
Mating effort
Mate finding
Reproductive effort
Investment in offspring/passing off gene
Trade-off: the more time you invest in finding a mate/multiple mates, the less
you invest in the offspring you produce with that mate/those mates.
o In many species, females invest more in offspring than males.
5% of mammal speices: males do a lot of investment in offspring.
On average, there is a tendency of male mammals who put a lot of their body
effort into finding mates
o Gender-specific intensity of intra-sexual competition for mates
How hard do members of one sex compete with e/o for mates?
Reproductive strategies
In general there is a lot of diversity in the living world.
Ecology and phylogeny modify how cost of reproduction affects parentazl investment
In fish species, parental care tends to come from male fish
o A lot of males do something that mimics raising offspring in the body, such as mouth
brooding
o Because these males fish end up with more surviving offspring, than if they try to find
another female mate
o Fish tend to have a polygamous mating system
In birds, parental care is usually shared between the male and the female
o Males have a huge opportunity to increase their fitness through helping raise offspring
with one or a limited number of female mates, rather than spending all their time
finding new mates
o Because of the biology of birds, both males and females provide care
o Thus monogamy is problem
o However, there are exceptions…but on average, it is usually monogamous mating
In mammals, it is strange…95% of mammal species, males don’t seem to invest anything in
offspring care.
o If males can out compete other males, males will tend to seek other females (polygyny)
o Female mammals tend not to do this
Evolutionary, females have kept babies to themselves
They invest heavily
Once they have fertilized offspring, the value of further mate diminishes
o High cost of reproduction for females, low cost of reproduction for males
o Males are limited by the number of mates available
Selective force on males to spend more effort in mate finding
Sexual selection: the basics
Imagine a population with 10 males and 10 females. In the case of mammals, each female has one
offspring. First of all there is no variation in reproduction success between females. Females are limited
by the resources they can invest in the offspring. They will only compete for the first mate
Males on the other hand, they don’t do anything for offspring. There is high variance in reproductive
success among these males. 6 males with no offspring, but the ones that did father offspring each had a
variable number of mates. There is a high fitness payoff for males to have more than one mate. This is a
byproduct of female-mammals having gestation and lactation. It pushes down opportunity for males to
have parental investment.
Males in polygnyous societies:
Aggressive to males
Grow weaponry
o For fighting other males
Grow defences
Larger at maturity (than females)
o They spend longer maturing
Mature later
Later fertility peak
Die sooner (than females)
Reproductive until death
Sperm competition
o Large testes
o To produce enough sperm for enough offspring

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Description
Ant 208: reproduction part 2 sex determination + sex differences o relate what we know about human sex differences to the evolutionary selective forces that produce these differences reproductive strategies o look at the differences in life history strategies that emerge from different gamete sizes o sexual selection: mate choice and parenting drives a lot of the differences we see between genders in the living world o sex differences: development and life history o ecological variation: secular changes there are changes across context based on the cues that individual bodies receive from their environments there are also changes over time (secular changes) reproductive health, bia gender o birthing, breastfeeding o sexual health many concepts are constructed currently in biomedicine, and raise the question that some conditions that are currently characterized as sexual dysfunctions may actually be side-effects of environmental mismatch, or they may be simply, culture bound misinterpretations of biologically very normal things. Sex determination biological sex and gender = function of phenotype product of genetic and environment -> single informational unit Ordered process o Chromosomal sex (fertilization) XX, or XY? o Gonadal sex (early fetal development) In the first six weeks: the emergence of gonadal sex Either the default production of female gonadal sex tissures, or in the presence of testes determining factor, the development of a different type of gonad (male gonads) o Phenotypic sex (accessory sex structures) Determined after puberty Chromosomal sex usually agrees with phenotypic sex (but not always!!) epigenetic influences o All sorts of environmental exposures can modulate gene expression during the lifespan o Modulate gene expression during lifespan o Early development has long-term effects, larger influence o Age, education, experience, conditioning Explaining sex differences Generalized differences between male and female o Bodies o Health risk and vulnerabilities Great interest in the past 25 years in global policy, public health, and feminist approaches to addressing gender inequities in health Health risks are also a product between evolved vulnerabilities and social contexts o support predictions of evolutionary theory These changes are what are expected in an evolved biological context Sexual selection theory o Predicts that there would have been many species, an evolutionary history of gender- specific selective forces o Gender-specific lifetime investment in Mating effort Mate finding Reproductive effort Investment in offspring/passing off gene Trade-off: the more time you invest in finding a mate/multiple mates, the less you invest in the offspring you produce with that mate/those mates. o In many species, females invest more in offspring than males. 5% of mammal speices: males do a lot of investment in offspring. On average, there is a tendency of male mammals who put a lot of their body effort into finding mates o Gender-specific intensity of intra-sexual competition for mates How hard do members of one sex compete with e/o for mates? Reproductive strategies In general there is a lot of diversity in the living world. Ecology and phylogeny modify how cost of reproduction affects parentazl investment In fish species, parental care tends to come from male fish o A lot of males do something that mimics raising offspring in the body, such as mouth brooding o Because these males fish end up with more surviving offspring, than if they try to find another female mate o Fish tend to have a polygamous mating system In birds, parental care is usually shared between the male and the female o Males have a huge opportunity to increase their fitness through helping raise offspring with one or a limited number of female mates, rather than spending all their time finding new mateso Because of the biology of birds, both males and females provide care o Thus monogamy is problem o However, there are exceptionsbut on average, it is usually monogamous mating In mammals, it is strange95% of mammal species, males dont seem to invest anything in offspring care. o If males can out compete other males, males will tend to seek other females (polygyny) o Female mammals tend not to do this Evolutionary, females have kept babies to themselves They invest heavily Once they have fertilized offspring, the value of further mate diminishes o High cost of reproduction for females, low cost of reproduction for males o Males are limited by the number of mates available Selective force on males to spend more effort in mate finding Sexual selection: the basics Imagine a population with 10 males and 10 females. In the case of mammals, each female has one offspring. Fi
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