Parental Investment

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  • Created by: Natasha
  • Created on: 31-12-12 14:46

A01 Parental Investment theory, Trivers, male, mil

Trivers (1972) proposed the Parental Investment Theory which claims there are substantial sex differences in parental investment which lead to different reproductive behaviours between men and women.

The theory claims that male investment in offspring is minimal due to their ability to produce millions of sperm which are not costly or time consuming to make. Therefore after the initial investment in mating, the male doesn’t have to invest in rearing or investing of the offspring. Infact with their minimal investment, the theory suggests that they should be promiscuous to gain greater reproductive success by mating with as many fertile females as possible.

On the other hand the theory claims that females investment in offspring is substantial due to the investment in supplying to the gamete, giving birth and heavy investment in rearing.  No matter how many males a female mates with in a single reproductive cycle, she can only become pregnant with one, therefore the theory suggests mating effort is less important in females. Furthermore the theory states females should be choosy in selecting a mate as they gain nothing from mating with males who do not stay around and provide resources for the offspring. Logically, by females being choosy, the genetic quality of the offspring would be of a higher quality which then insures a higher chance of reproductive success of the offspring resulting in spread of the parent’s genes in the gene pool. 

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A02 Frogs least will be more selective

Support comes from role-reversed species such as the Panamanian poison-arrow frog. The male frog invests more in offspring, whilst the  female frog are large and aggressive, competing for males who are selective about their partners. This supports the idea that parental investments influences reproductive behaviour, whereby the sex that invests least will be more selective about partners. 

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A02 Clark and Hatfield, females choosy

Supporting this theory, Clark and Hatfield (1989 and 1990) found 75 per cent of male students who were approached by an attractive female stranger agreed to have sex with them while none of the females agreed to have sex with an attractive male stranger. This provides evidence that men have evolved psychological mechanisms to ensure success in short term mating. These include a desire for sexual variety, the tendency to let little time elapse before seeking sexual intercourse, and a willingness to consent with strangers. 

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A02 Bias, sample students

However as this study was conducted on students, there may be difference between preferences in the age ranges of males so this study may be hard to generalise- lacking ecological validity. Also if the students were not alone when asked if a stranger was attractive, the extraneous variables would make the results inaccurate therefore lacking reliability as well as the possibility of demand characteristics and social disability. And if it provides evidence that they have evolved psychological mechanisms, the percentage should be 100 per cent if attractiveness is the only element. Attractiveness is also subjective to the individual; one male may find blondes attractive while one may find red heads attractive.  

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A02 Buss, youth fertility males

Trivers theory stated that males gain greater reproductive success by mating with fertile females, these mating preferences are supported by Buss’s (1989) cross-cultural study of preference in marriage partners in 37 cultures, involving 10,000 people. He found that males are tuned in to physical attractiveness as this signals youth and fertility which in turn leads to reproductive success as the older female’s eggs are the least likely for conception. In fact, he also found men who divorce and remarry tent to marry women who are increasingly younger than they are. Meanwhile he found women are tuned in to resources provided by potential mates as these will aid reproductive success by ensuring that offspring survive. 

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A02 Points to include

By the study being cross cultural and large sample size means the data is more representative of the population and therefore having high ecological validity. However by quantifying the data to draw conclusions may have cause lose to any usual results that could provide future research. Also is it right to compare cultures when some have arranged marriages and differences in social norms. For an example, in Western society the social norms make it more difficult for females to behave promiscuously (“nice girls don’t”) whereas these behaviours are encouraged in males.

Some critics have tried to explain male’s preference for younger women in terms of social power – younger women are easier to control, and therefore are preferred as mates. Kenrick et al (1996) effectively rejected this hypothesis. They found that teenage males are most attracted to women who are five years older than them, despite research showing such women usually show no interest in them and usually not more easily controlled by adolescent males. 

However, Trivers deterministic theory overlooks individual differences, that some women do have short-term relationships (one night stands), and many men choose not to behave promiscuously. 

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A01 Sexual strategies, Buss, Schmitt (short and lo

Sexual Strategies Theory (Buss and Schmitt, 1993) argues that both women and men purse short and long term relationships, but seek different qualities in short and long term partners. Women seek generous mates in short-term relationships as they use affairs and flings to test whether a male would be a suitable long term partner. While men look for very different things in one-night stands and long-term partners: a sexually willing partner is fine for a non-serious relationship, but for a long-term partner, faithfulness and good mothering skills are crucial.

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A02 Buss sexual jealousy

Supporting this theory, Buss (1993) studied the concept of sexual jealousy amongst males and females and concluded that a man whose mate was unfaithful would result in risking investment in offspring that were not his own (cuckolding) – which explains the reasons why they look for faithlessness in a long-term partner. Whereas women whose mate was unfaithful risked the division of resources, therefore he suggested that sexual jealousy may have evolved to be a solution to these problems.

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A02 Artificial 'imagine'

(expand) This is artifical as told to 'imagine', so lacks ecological validity. 

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A02 Reductionist

Like PIT, this explaination is reductionist, assuming simply genes account for preferences and reproductive behaviours. However, humans are complex, emotional beings. It may be the case that preferences and reproductive beahivour can be explained by other factors. They could be learned by observing and imitating models in media, whereby, if males observe other males having multiple short-term partners and seeking attractive 'fertile' women, that they will imiate such reproductive behaviours. Equally, operant conditioning could explain reproductive behaviours. If a man did contract a STD, this could be seen as a punishment and may learn to avoid short-term mates. 

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A02 Cultural differences, Christians sex


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A02 No explanation, homosexual relationships

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