Learning Table 5: Sex Differences in Parental Investment
Parental Investment is defines as ‘any investment by a parent in an offspring that increases the chance that the offspring will survive at the expense of that parent’s ability to invest in any other offspring (alive or yet to be born)’
(Trivers 1972)
AO2
AO1
Supporting and Contradictory Evidence
MAID
Males and females do not invest equally. Females’ initial investment is far
greater because female eggs are less numerous and more costly to create
than male sperm. A female can only have a limited number of offspring,
whereas a male can (potentially) have virtually unlimited. King Moulay
Ismail, a ruler of morocco, fathered 800 children, whereas the record for a
woman is 69 children (including 16 sets of twins, 7 sets of triplets and 4
sets of quadruplets- only 27 pregnancies).
One of the main differences is that men can opt out of parental investment
in a way that females can’t. Men tend to devote most of their effort to
courtship and mating and devote little to parental care (Daly and Wilson
1978). According to evolutionary theory, the best way for men to pass on
their genes to the next generation was to father many children (sleep with
as many women as possible), women on the other hand are more likely to
pass on their genes by carefully selecting a partner as mating is a lot more
costly for human females. Having few children will enable a female to
devote more time and resources and will ensure their survival.
Maternal Investment: Why do human females invest more?
The size of a human child’s brain has increased over time due to adaptive
pressures. To compensate for this, childbirth in humans occurs earlier in
the development, meaning that human babies are born immature
compared with other animals. Human females breastfeed their young and
are therefore burdened by the extended period of childcare. Therefore
human mothers make the greater prenatal contribution (9 months for
women compared with a deposit of semen for the man), but also make the
greatest postnatal contribution (breastfeeding for x amount of time).
Maternal Investment: The cost of maternal investment
In human females, the cost of childcare is high. The minimum parental
investment from a female is 9 months pregnancy followed by years of
feeding and carrying. The minimum paternal (male) investment would be a
few moments of copulation and some semen (Symons 1979). This means
that random mating is all the more costly for females.
Paternal Investment: Cuckoldry and Jealousy
When men do invest in offspring, they put themselves at risk of cuckoldry
(investing in offspring that isn’t theirs). Women will always know if a child
is theirs, whereas a man can never be 100% sure (unless they’ve had a DNA
test) that the child is theirs. Because of this, men will be more concerned
about sexual fidelity (whether their partner is sexually faithful to them)
(Miller, 1998). This is reflected in many laws across the world, whereby
women are treated more severely than men if they commit adultery.
Because of this, men are likely to be more jealous of sexual infidelity as
they are at risk of becoming cuckolded, whereas women are more jealous
of emotional infidelity, as they risk losing their mate to another women and
losing resources needed to bring up their child (Buss, 1995)
To summarise:

Both Males and females invest in their offspring to ensure that they
survive and pass on their genes. Males and females invest in ways
which will maximise the amount offspring they can produce.

Human females invest more because of biological sex differences
(carry the child for 9 months, breast feed etc.) and because of
immature status of infants (child born less developed because
human intelligence has evolved meaning bigger heads- mother can’t
carry the child for long enough)

Random mating is physically costly to females (9 months carrying
child plus x amount of years caring for child), physically very little
cost for males (finding a mate and semen)

Males experience sexual jealousy (fear of cuckoldry- investing
resources in a child that isn’t theirs), and women experience
emotional jealousy (fear that her partner will fall in love with
someone else and leave her with no resources)
 Maternal Investment
P- There is empirical evidence that supports the idea that women may try to cuckold her partner in order
to ensure an offspring’s survival.
E- Baker and Bellis (1990) conducted a survey in a magazine of over 2700 UK women. From the results
of this survey they estimated that as many as 14% of the population were products of extramarital mating.
Furthermore, Daly and Wilson (1988) found that some women compensate from their greater parental
investment by cuckolding their partners. This would benefit women as they may be able to get more
resources, and their new partner may have higher quality genes for her children.
E- This supports the idea that women may look elsewhere for a man with better genes while staying with
the partner that provides her with resources. This will enable her pass her genes on to a child that is
genetically higher quality, but will also ensure that she has the resources needed to ensure the child’s
survival.
L- Consequently, this increases the credibility of the evolutionary explanation of sex differences in
parental investment, as there is empirical evidence to support it.
 Paternal Investment: Men do Invest
P: There is contradictory evidence that refutes the idea that men devote most of their effort to mating and
devote little to parental care (Daly and Wilson 1978).
E: For example, Reid (1997) argues that human males may restrict their reproductive opportunities and
instead, invest more in each individual offspring.
E: This refutes the evolution assumption that males do not invest in their offspring and they only pass on
their genes to the next generation by fathering as many children as possible because it argues that males
contribute to parenting more by providing resources (e.g. stable food supply). This investment allows the
family to live in healthier environments, resulting in a decrease in infant and child mortality.
L: Consequently, this evidence reduces the credibility of the assumption that paternal investment is weak
because it does not account for that males invest in their own offspring for survival.
P- Additionally, further contradictory evidence refutes the idea of cuckoldry.
E-For example, Anderson (1999) measured the resources invested by fathers and stepfathers and found
that men appeared not to discriminate between children born to their current partner from a previous
relationship and their own children from a previous relationship.
E- This contradicts the evolutionary parental investment theory prediction that investment by fathers
would always be greater if they know the child is biologically theirs because fathers would only want to
invest in children that are carrying their genes, and wouldn’t want to invest in another man’s child.
Whereas this is not the case.
L- Consequently, this weakens the credibility of the evolutionary explanation of sex differences in parental
investment, as it doesn’t account for a parent’s investment in a child that isn’t genetically related to them.
 Paternal Investment: Sex differences in sexual jealousy
P- There has been empirical support for the evolutionary explanation of sex differences in parental
investment, particularly the differences in male and female jealousy.
E- Buss et al. (1992) found that male US students indicated more concern about sexual infidelity whereas
female students expressed more concern about emotional fidelity.
E- This is consistent the notion that men would want to risk becoming cuckolded and waste resources on
children that are not his, and therefore would be more concerned about the thought of a partner having a
sexual relationship with another man. Women wouldn’t want their partner to be emotionally involved
with another woman as that may mean a loss of resources if their partner left them.
L- This increases the credibility of the evolutionary explanation of sex differences in parental investment
as there is empirical evidence which supports its assumptions.
 Methodological Issue (MAID)
P- However, such studies have low population validity, which means that the results cannot be generalised
to the whole population.
E- Buss’s study was conducted on university students in America
E- This is an issue because students may have a different view about relationships than the rest of the
population; they tend to have many short-term relationships because they are more mobile (Moghaddam,
1998). This may mean they have short-term sexual relationships rather than long term emotional ones.
Also because the study was conducted in America, it can’t be generalised to non-western cultures as they
have different social norms such as arranged marriages, or polygamous relationships.
L- Consequently, the support such studies give to the assumptions of sexual jealousy between men and
women can be reduced because the validity of them can be questioned. Therefore the credibility of these
assumptions is weakened because the studies used to support them can be falsified.
 Debate: Reductionist
P: One weakness of the evolutionary explanation of sex differences in parental investment is that it is reductionist.
This is because it reduces parental investment down to sex differences such as the length of time a woman carries a
child.
E: Although this allows complicated behaviours to be scientifically tested and allow for further
research/explanations to be developed; taking a reductionist approach does not allow us to look at parental
investment from the whole individuals’ perspective.
E: For example, Rowe (2002) suggests that an evolutionary perspective of paternal investment is limited, and that
men’s parental behaviour depends on various personal and social conditions. For example, it does not consider that
a man may want to invest in a child because they feel unconditional love towards them, or that they had a father
that invested a lot in them and have therefore learned to invest by observing that behaviour. Furthermore, Belsky
(1991) claims that childhood experiences such as parental divorce tend to correlate with the degree to which men
invest in the upbringing and care of their own children. This means that what happened in a person’s childhood
may have a greater influence on the amount they invest in their offspring, rather than purely evolutionary factors.
L: Therefore parental investment theory is arguably too simplistic in its explanation of parental investment.
Therefore its explanatory power is weakened as it is arguably an inadequate explanation. A more holistic view
should be considered when researching parental investment.
Debate: Nature vs Nurture
P: Another issue with evolutionary explanation of sex differences in parental investment is that it takes the view
that how much a person invests in their offspring is purely due to nature.
E: This is an issue because it doesn’t take into account any factors that can be classed a nurture i.e. environmental
factors.
E: For example, Belsky (1991) claims that childhood experiences such as parental divorce tend to correlate with
the degree to which men invest in the upbringing and care of their own children. This means that what happened in
a person’s childhood may have a greater influence on the amount they invest in their offspring, rather than purely
evolutionary factors, suggesting that nurture can have an effect on parental investment and that it isn’t entirely due
to nature.
L: Therefore the evolutionary explanation of sex differences in parental investment can be seen as less credible as it
doesn’t take into consideration any factors that may come from nurture.
Debate: Determinism
P: Another weakness of the evolutionary explanation of sex differences in parental investment is that it can be said
to deterministic.
E: This is because it suggests that the amount of parental investment is predetermined and therefore ‘fixed’ by the
sex of a person.
E: This is an issue simply because the fact someone is male doesn’t mean that they will want to try and produce as
many offspring as possible and invest less in their own or even someone else’s offspring. Therefore it doesn’t
account for the fact a man can have a choice and choose to invest in children that aren’t genetically their own, or
women that return to work straight after having a child. Furthermore it doesn’t account for modern times where
women may return to work and men now may stay at home to raise the children. Hence, this explanation does not
consider that all individuals have free will.
L: Consequently, this weakens the explanatory power of parental investment theory because it doesn’t offer a full
account into the investments and choices that each sex makes into the raising of offspring and sex differences in
parental investment.
Other potential MAID points:

Gender Bias: Alpha Bias – exaggerating the differences between men and women in terms of Parental
Investment

Other Methodological Issues

Socially Sensitive Research

Culturally Biased
NB
Make sure you give DETAIL throughout your answers in your A01 and A02. A01 needs to be
detailed, accurate and concise; A02 needs to be full PEEL paragraphs with DETAIL and
clearly LINKED to the question. Make sure you use words from the QUESTION in EVERY
paragraph you write in order to answer the question EFFECTIVELY.
Your A02 points HAVE to be a mixture of OUTCOME STUDIES (supporting/contradicting –
around 3 in full PEELS) AND MAID SYNOPTIC POINTS. Show a BREADTH and DEPTH of MAID
points where possible. BUT MAKE SURE THESE MAID POINTS ARE IN FULL DETAIL AND
LINKED TO THE QUESTION THROUGHOUT (DO NOT LEAVE THEM ALL TO THE END).