Variation within species Variation is passed on through inheritance More offspring are produced than survive Selection pressures, selects those with the best adaptations Those best adapted survive to pass on their genes Therefore human reproductive behaviour is an adaptive trait to increase the survival of the organisms genes. 2 types of sexual selection Intersexual selection – selection of characteristics between the genders (female strategy) Intrasexual selection – competition within the species, the sex that invests the least will compete over the sex that invest the most (male strategy) Depending on the type of sexual selection, human reproductive behaviour differs

Buss 30 countries, 37 cultures Males prefer attractive, young females Females prefer ambitious, older males Davis Studying personal adds, Females emphasised their attractiveness and youth, Males emphasised there success and wealth Singh Males prefer a low waist-hip ratio in females Concar Symmetry is physically attractive, due to an indicator of good genes Fishers runaway hypothesis Females choice is determinate of desirable characteristics shown by the opposite sex These desirable characteristics will increase her offspring's chance of survival, hereby the survival of her genes Zahavi’s handicap hypothesis Females choice is determinate of the survival of the opposite sex, despite an apparent handicap, this is an indicator of good genes

Males are more promiscuous to enhance their reproductive chances Schmitt – Sociosexual Q, 48 nations, participants Males were universally more promiscuous Short – link between promiscuity and testicular size (Sperm competition theory) Animal observations Gorillas less promiscuous and have small testicular size : Chimps more promiscuous and have a large testicular size Humans are not has promiscuous as chimps but neither as monogamous as gorillas Hatfield More males than females were willing to have on the spot sex, when asked by a stranger compared to females.

Intra/intersexual selection doesn’t take account of kin selection increasing the reproductive success Fellner + Marshall The closer the genetic relationship, the more altruistic behaviour, 80% parents would give a kidney to their child. As evolution is biological fact, we would expect it to be universal, in factors such as mate choice Strassburg On internet dating sites, males preferred wealthy, ambitious females compared to young and attractive ones.

Trivers – Parental investment Differences in parental investment determines who is going to be the more choosy sex (Intrasexual selection) Females are the more choosy sex, due to higher parental investment Schmitt – Males are more universally promiscuous : females Due to the greater reproductive cost there is increased likelihood of being more protective and sacrificial Fellner + Marshall – the closer the genetic relationship, the more we are willing to sacrifice in order to maintain the survival of their genes (kin selection) Factors determining parental investment and therefore the sex differences: Anisogamy (difference in the size of the sexual gametes) – Females egg, is much larger and is produced at a larger reproductive cost, limited supply : Males sperm, which is small and produced indefinitely has a lower reproductive cost. Reproductive cost (female has the greater burden) – Females have to go through gestation and lactation Parental certainty (females have this due to internal conception) – Ridley F: only 20% of children in the UK have a true biological father as their dad Proximity (the adult closest is responsible for care) – Female due to internal conception is often left holding the baby whilst males “run away”

Suggest that reproduction is the sole motivator for the formation of a relationship, however other theories e.g. reward/need satisfaction state that the formation of relationships is due to rewards. Foa + Foa state that rewards in a relationship include, money and love Parental investment only takes account of biological offspring, however it doesn’t take account of adopted children, which don’t involve many of the factors in parental investment such as anisogamy, and parental certainty, so why would there be a need to still protect them Psychological explanations to mating strategies such as reward/need satisfaction may offer a more valid, modern approach. Due to evolutionist explanations are factual and not subject to variation, therefore they are reductionist and determinist.

Selfish Gene – Offspring only contain 50% of parents genes, therefore there will be a conflict of interest. Parents want to invest in the survival of many offspring : Offspring want to invest in themselves Parent will want to reserve recourses and only give the minimum care necessary for survival Offspring will want care until they can become independent. Offspring want more food than the parents are willing to give them Parents interest to kill offspring to bring about reproductive cycle of females more quickly Offspring compete for resources, sometimes injuring/killing their siblings. Increases offspring’s “fitness”, but decreases parents “fitness”