Key concepts in play and sex differences

Play is a common activity seen in young animals across many species, often mimicking behaviours that adults perform. This behaviour is voluntary and may help in developing skills useful for survival, making it potentially adaptive. In humans, differences in play styles and toy choices often appear between boys and girls from an early age.

Sex differences in toy preferences

Sex differences refer to variations in behaviour or preferences between males and females, such as boys with XY chromosomes typically choosing toys like cars, while girls with XX chromosomes often prefer dolls. These patterns raise questions about their origins.

Socialisation

Socialisation is the process through which individuals learn societal norms and expectations, often leading to the belief that toy preferences stem from cultural influences. However, researchers like Hassett et al. suggested that biological factors could also play a significant role.

Sex hormones

Sex hormones are chemicals like testosterone and oestrogen that influence brain development and behaviour. These hormones might lead to differences in how males and females engage with toys.

Background to the study by Hassett et al. (2008)

Research on conditions like congenital adrenal hyperplasia (CAH) - a disorder where individuals with XX chromosomes are exposed to higher levels of male hormones - showed that affected girls often preferred toys typically associated with boys, even when encouraged otherwise.

Earlier studies with monkeys also revealed similar patterns: male monkeys interacted more with "masculine" toys, while females favoured "feminine" ones. Since monkeys are not influenced by human cultural norms, this suggested that toy preferences might be biologically driven rather than solely learned through socialisation.

Aims of the study

1. To examine differences in toy preferences between male and female monkeys when given a choice between a stereotypically feminine toy (plush) and a masculine one (wheeled).
2. To support the idea that biological factors, rather than cultural influences, drive sex differences in toy preferences in humans.

Methodology and design

The research was conducted as a laboratory experiment using an independent measures design, where groups are compared without participants experiencing all conditions.

Key variables

• Independent variable - The sex of the monkey (male or female).
• Dependent variable - The time spent (in seconds) interacting with either a wheeled toy or a plush toy.
• Additional factors recorded included the monkey's age (juvenile or adult) and social rank, determined by observing behaviours like grooming.

Sample details

The sample consisted of 135 juvenile and adult rhesus monkeys. After exclusions - 14 for prior hormone research participation, 39 infants due to difficulty identifying sex - the final analysis included 23 females and 11 males. These were selected through opportunity sampling, focusing on those who interacted with toys at least five times.

Data collection techniques

Observations were non-participant and covert, meaning researchers watched without interfering and without the subjects' awareness of being studied. Seven 25-minute sessions were video-recorded in the monkeys' outdoor enclosure, with two observers using a behavioural checklist to code interactions from the footage.

The procedure - Controlled presentation of toys to observe natural preferences

1. Monkeys were kept indoors while toys were placed in the enclosure, 10 metres apart, with positions counterbalanced (switched left to right across sessions) to avoid bias.
2. Different pairs of toys were used each time, such as a wagon with a teddy or a truck with a Scooby-Doo plush.
3. Video recordings captured interactions, with observers noting duration in seconds and specific behaviours like holding or dragging.
4. Any unclear behaviours were discussed between observers for agreement.

Controls and ethical considerations

Several controls ensured reliability:

• Toys were positioned consistently to prevent location influencing choices.
• Toy positions were counterbalanced.
• Monkeys remained in their familiar environment to encourage natural behaviour.

Ethical guidelines followed the Guide for the Care and Use of Laboratory Animals, including:

• Housing in a 25 m² outdoor enclosure with a temperature-controlled indoor area.
• Constant access to water, daily food like monkey chow, and fresh fruit and vegetables.
• Oversight by the Emory University Institutional Animal Care and Use Committee to ensure welfare.

Results of the study

The findings highlighted clear patterns in toy preferences, with comparisons to human data showing similarities.

Key findings on preferences

• Among males, 73% preferred wheeled toys, 9% preferred plush toys, and 18% showed no preference.
• Among females, 30% preferred plush toys, 39% preferred wheeled toys, and 30% showed no preference.

Comparison with human data

• In humans, males spent more time with masculine toys than feminine ones, while females showed a slight preference for feminine toys.
• In monkeys, males interacted more with wheeled toys than plush, with females showing a minor preference for plush.

These results indicated that sex differences in preferences are similar across species.

Conclusions from the study

The study concluded that toy preferences in both monkeys and humans are influenced by hormonal sex differences. These biological differences lead males and females to prefer different activities. Differing activity/play preferences lead to sex differences in cognition and behaviour.

Evaluation of the study

The study has both strengths and weaknesses, which can be assessed in terms of reliability, validity, and generalisability.

Issues and debates

Nature versus nurture

The results lean towards nature, emphasising hormonal influences on toy preferences over cultural nurturing. Males displayed stronger preferences than females, but social rank also played a role.

Applications to everyday life

Insights from the study can inform toy design and marketing, encouraging toys that build diverse skills. For boys, wheeled toys with expressive faces might foster empathy and language. For girls, toys with moving parts in social scenarios, like a bus with dolls, could enhance visuospatial abilities.

Use of animals in psychological research

Using monkeys allowed control over environmental variables and eliminated cultural confounds like gender norms from advertising or peers. This strengthened validity for biological explanations, though extrapolating to human children requires caution due to species differences.