In one line: Animal models let researchers change what people's lives cannot be changed to test, and measure what cannot be measured in a living person.
Does the care a baby receives shape how it copes with stress as an adult? No researcher could give some babies less care to find out. With rats, it can be studied.
An animal model is used on the assumption that the process works in a similar way in both species. Rats and humans share the main parts of the stress system.
What an animal model makes possible
Manipulate
Change what could never be changed in a person's life, such as early care.
Control
Hold genes, diet and housing constant, so one cause can be isolated.
Look inside
Examine brain tissue and genes directly, which no living person allows.
Lifespan
A rat is an adult at about three months, so a whole life can be followed.
Manipulate · Control · Look inside · Lifespan
Remember: Change it, control it, look inside it. That is what the animal adds.
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Key idea: Weaver and colleagues (2004) showed that a mother's care can change how her pups' genes work, and so how they handle stress for life.
Weaver et al. (2004)
Care
Some rat mothers lick and groom their pups a great deal; others very little.
Swap
Some pups were cross-fostered. This separates the mother's genes from the mother's care.
Gene
Pups given little care had a gene for handling stress hormone switched down in the hippocampus: methylation.
Stress
As adults, these rats had a stronger stress response. It followed the mother who raised them, not the mother who bore them.
Care · Swap · Gene · Stress
Cross-fostering is what makes the study strong. Because care was separated from genes, the difference can be put down to the care.
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Key idea: An animal finding becomes evidence about people only when it is checked in people.
Rats
Weaver et al. (2004)
- Little care, gene switched down
People
McGowan et al. (2009)
- Brains studied after death
Same pattern
the check
- Abuse in childhood, gene switched down
McGowan and colleagues examined the brains of people who had died by suicide. Those who had been abused as children showed more methylation of the same stress gene than those who had not.
That supports the rat finding, but it is correlational: the researchers could only compare people, not change their childhood. The experiment was possible in rats only.
Exam tip: The strongest use of an animal study pairs it with a human study that points the same way.
Key idea: Animal research buys causal evidence with control, and pays for it in how far it applies to people and in harm to the animals.
Strengths
- Cross-fostering isolates care from genes: a causal claim
- Genes and brain tissue can be examined directly
- A human study found the same pattern
Limits
- Licking and grooming is not human parenting
- Human stress involves thoughts that rats lack
- Separating pups from mothers causes distress
The distress raises responsibility. As in 1.6.2, the study must follow the 3Rs and pass a cost-benefit review by an ethics committee.
Weaver's design caused little harm: the pups stayed with a mother, and care varied naturally. That is part of why it is widely accepted.
Remember: Causal in rats, correlational in people, justified only if the harm is small.
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How this is asked: Paper 1 asks for animal research with one example [4], in an unseen study [6], or as an essay in a context [15].
In the 6-mark question the study is given: every point must be about it.
Context: Learning and cognition. Researchers investigated the role of sleep in memory. Mice learned where food was hidden in a maze. Half were then kept awake for five hours; the other half were allowed to sleep. The next day, the mice that had been kept awake made more errors finding the food. With reference to this study, explain the use of animal research in the study of human behaviour.
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