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TASK- Identify AMRC (Aim, Method, Results and Conclusion), including IV, DV,
experimental and control group.
Males are more aggressive than females in almost every species. Why is this? One possible
reason could be in the influence of the male sex hormone, testosterone. Testosterone is
produced in the testes of males, which could be why males are more aggressive than females.
While it is also produced in the ovaries of females, this is at a much lower rate. Perhaps it
doesn’t come as a surprise that there have also been correlations found between violent crime
and testosterone levels (e.g. Dabbs et al., 1997 as cited in Batrinos, 2012; you can read more
Numerous animal studies have shown that castration (cutting out the testicles) will reduce the
aggressive tendencies in males. The following study by Albert et al. (1986) is a good example
of a well-controlled experiment that demonstrates a causational relationship between
testosterone levels and aggression.
Albert et al. (1986) wanted to investigate the effects of changing testosterone levels on the
aggressiveness of male rats. They placed rats in cages and identified the alpha males. An
alpha male is the leader of the colony. In animals, this is typically the biggest and strongest.
The term can be applied to any animal group, including humans. So the researchers identified
the alpha males and they measured their aggression levels when there was a non-aggressive
rat placed in the same cage. They measured aggression by recording behaviours such as
After they measured the aggression levels they divided the alpha males into four
separate groups to undergo four separate surgeries:
A. Castration
B. Castration followed by implanting of tubes with testosterone
C. Castration followed by implanting of empty tubes
D. A “sham” castration followed by implanting of empty tubes (this means they would have
cut open the rat and sewn it back up without actually removing the testicles).
They then measured the change in aggression when non-aggressive rats were introduced to
the cage. Those that had the operations that reduced testosterone levels (e.g. Group A and C)
had a decrease in aggressiveness (e.g. attacking and biting) but those that had the operations
that kept testosterone levels in tact (Group B and D) didn’t have a significant change in
aggression levels.
This evidence by itself demonstrates a correlation between testosterone and aggression. It
was followed by a second operation so that those that had the surgery that decreased
testosterone had another operation that increased testosterone (e.g. Group C had their tubes
filled with testosterone). Those alpha rats that had their testosterone replaced showed
returned levels of aggressiveness similar to those in the “sham” castration group.
You can find the original study here