Evolution (Edexcel A-Level Psychology): Revision Notes
Evolution
What is evolution?
Evolution describes the gradual development of different species of living organisms from earlier ancestral forms throughout Earth's history. This process explains how all species share common ancestors and have diverged over time.
The mechanism driving evolution is natural selection, whereby organisms better adapted to their environment tend to survive longer, remain healthier, and reproduce more successfully. These advantageous traits are then passed to offspring through genes – units of heredity containing DNA that carry information from one generation to the next. Each gene influences development by triggering the production of specific enzymes and proteins involved in cell production.
Worked Example: Natural Selection in Giraffes
Consider giraffes that historically depended on tree foliage as their primary food source. Those with naturally longer necks could reach higher foliage, giving them a survival advantage.
Step 1: Variation occurs through random mutations – changes in genetic structure that make individuals different from others of the same species.
Step 2: Giraffes with slightly longer necks gained advantages in accessing food, making them more likely to survive to reproductive age.
Step 3: Because they reproduced more successfully, their advantageous genes (longer neck versions) were passed on whilst shorter-necked giraffes' genes died out.
Result: Over extended periods, the frequency of certain traits within a population shifts through this process.
This mechanism is known as sexual selection – a form of natural selection where individuals successful in attracting mates out-reproduce others in the population. Over time, traits that enhance reproductive success become more common.
Evolutionary psychologists argue that human mental processes and behaviours have evolved similarly to physical characteristics. They suggest aspects of human behaviour result from evolutionary adaptations that served purposes in our ancestral environment.
How does this explain behaviour?
The brain, like any other physical organ, develops according to the genetic blueprint inherited from parents. Brain structure and function have evolved to serve adaptive functions in the environment of evolutionary adaptedness (EEA) – the conditions prevailing when a species first began responding to environmental pressures. For human psychology, the EEA of interest is when humans lived in hunter-gatherer groups, as this is when behavioural characteristics became 'hardwired' into brain structure.
During the EEA, successful humans possessed traits that suited their environment. Evolutionary psychologists examine fossil records to understand the EEA and speculate about adaptive behaviours. They then match these historical behaviours to current universal behaviours shown by modern humans, arguing that behaviour is genetically determined through brain structure and chemistry.
Examples of evolutionary-influenced behaviour include:
- Parental investment – caring for offspring to ensure their survival
- Mate choice – selecting partners with desirable traits
- Understanding emotions – recognising and responding to emotional states
Modern Mismatches
Whilst our genetic makeup evolves slowly, environments can change rapidly. This creates potential mismatches where we remain influenced by 'hardwired' behaviours that once served us well but may clash with modern living.
For instance, humans possess a predisposition to consume calorie-dense foods – useful when we were foragers with uncertain food supplies, but now a driving force behind obesity epidemics in societies with abundant food.
How does this explain aggression?
In evolutionary terms, success is measured by producing offspring that survive to reproductive maturity. During the EEA, successful males were typically physically larger and stronger, making them most capable of providing food and protecting mates and offspring. Psychologically, males who displayed greater aggression when resources were threatened or when hunting would have possessed adaptive advantages. Such males may also have been prepared to attack other humans and seize their resources to provide for their families.
This created advantages in mate choice. Successful females selected mates who provided favourable genes, so larger, stronger males were preferred. These males were also more likely to provide superior resources through food acquisition and protection, suggesting that males displaying aggressive traits would be more successful than non-aggressive males. Consequently, competition for mates has driven the development of masculine aggression.
Female Aggression Patterns
The theory also predicts females would display less physical aggression. From an evolutionary perspective, physical aggression would be disadvantageous for females who spend extended periods pregnant, breastfeeding, and caring for vulnerable young children to ensure their survival. Engaging in physical conflict would put themselves and their offspring at risk, threatening their survival.
According to evolutionary psychology, this has resulted in female aggression being less physically violent and more verbal and emotional in nature.
Buss (1999) proposed that whilst females compete less physically for mates, they still compete for the best partners. However, females achieve success by denigrating other females to potential mates, making rival women appear less attractive. Experimental research has provided some support for this hypothesis.
If these evolutionary ideas hold validity, we would expect physical differences in male and female brain structure and chemistry, leading to greater aggression expression in males. We would also expect greater aggression amongst males than females, and animals closely related to humans genetically should show similar behavioural patterns.
Evaluation
Male brains do exhibit minor structural differences compared to female brains, partly attributable to substantially higher testosterone exposure before and after birth. These differences have been linked to typical male attributes and abilities such as spatial awareness and aggression, both advantageous in the EEA. Extensive experimental evidence suggests testosterone levels are associated with aggression. For example, Mazur (1983) demonstrated a marked increase in inter-male fighting around puberty when rapid testosterone increases occur.
Supporting evidence comes from research examining current patterns of violence where sexual jealousy is frequently cited as a major cause of aggression between males and within couples (Sprecken and Wenzel, 2004). Males may be biologically driven to protect their reproductive resources from male competition.
Major Limitation: Post Hoc Reasoning
Evolutionary theories are ultimately 'post hoc' arguments – theories developed retrospectively to fit observed facts. These ideas are difficult to prove as they cannot be scientifically tested; fossil records for behaviour are limited, and though evolutionary theories make logical sense and can explain observed facts, they cannot be empirically tested as we cannot access the EEA.
Key Points to Remember:
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Evolution through natural selection explains how advantageous traits become more common in populations over time as better-adapted organisms survive and reproduce more successfully.
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Sexual selection drove aggression differences: males evolved greater physical aggression for resource competition and mate acquisition, whilst females evolved less physical aggression due to childcare responsibilities, instead competing through verbal and emotional means.
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The environment of evolutionary adaptedness (EEA) refers to hunter-gatherer conditions when human behavioural characteristics became hardwired; modern behaviour sometimes reflects mismatches with current environments.
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Supporting evidence exists from brain structure differences and testosterone research (e.g., Mazur 1983), though evolutionary explanations are 'post hoc' arguments that cannot be empirically tested as we cannot access the EEA.
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The approach raises debates about biological determinism (potentially excusing violent behaviour) and reductionism (oversimplifying complex behaviour by ignoring social learning and other environmental factors).