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Lecture 8

ANT208 Lecture 8

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Dan Sellen

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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