EXPLAINING AGGRESSION THROUGH EVOLUTION
OUR ANCESTORS WERE IDIOTS

Charles Darwin published The Origin Of Species in 1859. His Theory of Evolution (sometimes called "Darwinism") changed the way human beings understand themselves. The Theory of Evolution proposes that humans are a species of animal and that modern humans have evolved from ape-like ancestors that lived 6 million years ago.

STOP!

Stop right there.

"Ape-like ancestors".

NOT "apes". Chimpanzees and gorillas and orangutans are apes. We're not descended from them. But they are descended from the same "ape-like ancestors" as us, 6-16 million years ago.

NOT "monkeys". Monkeys have tails. Monkeys are a different group of animals. We're not descended from monkeys. But our ape-like ancestors and monkeys are both descended from some earlier animals that lived 20 million years ago.

It looks like this:

Don't let anyone tell you that we're descended from apes. Apes might feel offended by that. But us and the apes share a common ancestor; together, we're known as the "hominids"

The idea that one species could turn into another is hard to imagine, but the evolutionary process is based on three simple ideas:

Natural selection is sometimes described as "descent with modification". This is the idea that some animals are better suited to survive than others. Animals that have survival traits will live slightly longer and produce more offspring than animals that don't have them. They pass these survival traits on to their descendants. Gradually, the survival traits become more and more common till eventually all the descendants have them: they have been modified. Those that don't have the modifications die out.

Survival traits are anything that helps an animal survive and reproduce. This can be things like speed and strength, but it can also be cunning or stealth. Things that attract mates (like the lion's mane or the peacock's tail feathers) are survival traits. So are things that help reach food (like the giraffe's long neck).

Humans have many survival traits. Important ones are intelligence, team work and using tools.

Aggression is an important survival trait, which is why the limbic system and hormones produce aggression. Too little aggression and you don't get to eat or reproduce, too much and you get killed (like Higley's rhesus monkeys).

Genetic mutation is the idea that children are never the exact genetic copies of their parents. When reproduction occurs, the mother and the father both donate genes to the child, but the copying of genes isn't exact. These genetic differences are mutations.

Did someone say "mutants"?

Mutations don't give you exciting super powers. In fact, most mutations are bad, making you slightly more susceptible to some illness or another (like cancer or diabetes).  But occasionally, a genetic mutation gives a slight advantage, like strength or a longer neck or more impressive feathers. A mutation like this becomes a survival trait.

When long periods of time pass, the tendency for genetic mutations to be naturally selected as survival traits add up and creatures can change massively, eventually becoming a different species altogether (this is "speciation"). Creatures with very short lifespans, like mayflies and viruses, can evolve dramatically in just a few years; creatures, like humans, with longer lifespans take millions of years to evolve.

Don't think that some creatures (like humans) are "more evolved" than others. They're not. All life forms are evolving. Because humans can use technology to alter their environment, there may be less pressure on us to evolve. Sharks are a good example of animals so well-adapted to their environment that they haven't shown many evolutionary changes in millions of years.

Physical appearance and abilities aren't the only things that change because of genetic mutation and get passed on because of natural selection. Behaviours and thought processes change this way too. Evolutionary psychology looks at how our brain structures, our behaviours and our cognitions have been shaped by evolutionary processes.

9-minute video with a very simple explanation of  Darwin's discoveries and natural selection

"Survival of the Fittest"

"Survival of the Fittest" is a phrase often wrongly attributed to Darwin (it was Herbert Spencer who used it to describe Darwin's theory). It sums up the Theory of Evolution in 4 words.

But bear two important things in mind about this phrase:

1. What survives is not the fittest creature but the fittest genes. If a gene produces a survival trait (like speed or size or intelligence or aggression) it will survive because it will be passed on to children and grandchildren
2. "Fittest" means "most suitable" or "most adaptive". It doesn't necessarily mean "strongest". A gene for intelligence or attractiveness might be fitter than a gene for strength or size. After all, intelligent and attractive people are more likely to marry and have children than big, strong people, right?

THE EVOLUTION OF AGGRESSION

Aggression is a human behaviour that may have evolved over time. Obviously, living together peacefully with other humans is an important survival trait and if anyone couldn't do that, they would be unlikely to live long enough to pass on their antisocial genes.

However, in other ways aggression may also be a survival trait. Our ancestors needed to use aggression to defend themselves and their children from predators. They also needed to use aggression to catch food. Aggression has fitness and so genes which produce aggression will survive.

The most important survival trait is therefore the ability to switch aggression on and off. This is what the limbic system seems to do.

• The amygdala interprets threats and produces aggression or fear - the "fight or flight" response
• The hypothalamus triggers the production of testosterone when there is a threat
• The thalamus passes the warning to other parts of the brain, causing serotonin levels to drop and dopamine levels to rise

In humans, there is an additional complication because the pre-frontal cortex can consider these messages (which appear in your mind as "feelings") and decide to overrule them. This ability to ignore our instincts and choose whether or not to act aggressively is what enables humans to live together in complex groupings - another survival trait.

THE ANIMAL MODEL

One consequence of the Theory of Evolution is that animals can tell us a lot about human behaviour. Studying animals to learn about humans is called ethology.

Lots of studies into aggression use the animal model, especially studies that focus on the "old brain" areas like the amygdala, which we share with many other animals.

Animal studies like this include John Flynn's study of cats,  Higley et al.'s study of rhesus monkeys and Ferrari's study of rats.

APPLYING THE EVOLUTION OF AGGRESSION TO REAL LIFE
AO2

Sexual Jealousy

Sometimes aggression makes it difficult for humans to live together. Jealousy is a good example. Becoming aggressive towards another male who is interested in the same woman as you is another survival trait: if you allow another male to have sex with the woman you desire, then your rivals genes will be passed on, not yours. Women also feel jealousy, because if the male who you wish to father your children  has sex with other women, other women's genes will be passed on at the expense of your own.

This explains why men and women experience jealousy and why it may lead to aggression. It also explains why we like jealousy in our partners (up to a point) - jealousy has "fitness" so we have evolved to find it attractive.

Not too much jealousy, though. We have evolved a pre-frontal cortex so we can resist our jealous impulses. Someone who is irrationally jealous is NOT attractive. Their behaviour is a sign of weakness and we have evolved to find weakness unattractive. Of course, we're all genetically different; some of us have genes that make our jealous urges particularly strong and some of us have genes that find strong expressions of jealousy particularly attractive.

Emotions (including revenge, spite, happiness, anger) must have evolved because most of the time they motivate fitness-enhancing behaviours, and that is surely true for humans as for other animals
 - Elizabeth Cashdan (2009)

David Buss (1988) identified two mate retention strategies used by males to control their partners: direct guarding of the female restricts her movements; negative inducements to prevent her straying include things like financial control or the threat of violence.
 
Shackleton et al. (2005) surveyed 461 men and 560 women in committed relationships. They found a positive correlation between men who used mate retention techniques (direct guarding and negative inducements) and their use of violence. The women’s results confirmed this correlation. Men also tended to use emotional manipulation as a mate retention technique – a form of non-physical aggression.

Social Aggression

Not all aggression is physical aggression. There is also teasing, name-calling, rumour-spreading socially excluding people. Social aggression has two components:

• Indirect aggression, which is covert (hidden), such as spreading malicious gossip
• Relational aggression, which is overt (in the open) but non-physical, such as breaking off a friendship, pulling faces or “bitchiness”

Aggressive behaviour helps an animal protect itself and prosper, but only up to a point. If it is too aggressive, it may be rejected by the group or even attacked. Therefore, social aggression has more survival value than physical aggression: it has the same benefits without the risks.

Why do we put up with social aggression? As with other types of aggression, it has fitness, but only up to a point. Social aggression allows members of the group who may be physically weak but verbally or socially skillful (quick-witted, perceptive, good at lying) to achieve power without the risks that come from physical confrontations. This is a survival trait for them and other members of the group might benefit too since social aggression might unite the group against an unpopular minority or keep potential troublemakers from being too active.

This ties in with Tajfel's Social Identity Theory, that we naturally form ingroups and discriminate against outgroups. Evolutionary psychology explains why we have an urge to do this.

One of the reasons we're still here and sabre-toothed tigers aren't is that humans evolved to use social aggression instead of physical aggression... most of the time

EVALUATING THE EVOLUTION OF AGGRESSION
AO3

Credibility

Darwin's theory of natural selection is a well-established scientific theory with a huge amount of supporting evidence. Modern science has identified the role that many genes play in hereditary features. The theory that brain structures or processes that enhance fitness will be passed on as survival traits is logical and matches with what is observed in animal and human studies.

This evidence supports the nativist viewpoint that aggression is innate, present from birth and an unavoidable (and even a positive) part of human behaviour.

Objections

The Theory of Evolution accounts for some instances of aggression, but not all. There is some aggression that clearly has survival value, but much that does not. For example, aggressive animals tend to die younger and don't get to pass on their genes. Darwin's theory has been expanded over the years to account for this, bringing in ideas like group selection (behaviours which benefit a group are selected for fitness, and a group as a whole might benefit by having some aggressive members to defend it) and kin selection (aggressive behaviour might put an individual at risk, but they protect their mates or offspring and therefore help their genes to survive even if they don't).

Some people reject the Theory of Evolution for religious reasons. For example, they argue that natural selection contradicts the account of Creation given in the Bible or it suggests that humans are here by chance. However, since Psychology is a scientific discipline (or tries to be) and the weight of scientific evidence supports the Theory of Evolution, psychologists must consider evolutionary explanations as possibilities, even if such an idea goes against their personal beliefs.

Differences

The Exam Board expects you to compare the evolutionary explanation of aggression with the Freudian explanation of aggression. Freud's ideas are explained on another page. For now, I'll compare and contrast the biological explanation with the empiricist explanation that aggression is learned.

The evolutionary explanation of aggression supports the nativist (nature) view of human behaviour, but the Learning Approach takes the situationalist (nurture) view that all our behaviour comes from our environment.

Strict Behaviourists like B.F. Skinner would argue that ALL behaviour is learned and that human beings are born as tabula rasa (a bank slate), with behaviour like aggression being added later.

Biological determinists would argue that ALL behaviour is hereditary. Because we have evolved from aggressive animals, we have an inbuilt urge to be aggressive.

Most psychologists take a middle way between these extremes. Genetics gives us predispositions to behave a certain way, but we can resist these impulses if we try. Although we have evolved from aggressive animals, we have also evolved from cooperative animals. Aggression and cooperation are both part of our genetic inheritance.

Applications

If we have evolved from aggressive animals, then aggression is part of our nature and cannot be removed. The best we can do is accept it and learn to live with it.

Raymond Dart (1953) took this idea and proposed the "Killer Ape Theory". This is the idea that humans are descended from particularly aggressive ape-like ancestors and that war and aggression have been the driving forces in human evolution. According to this gloomy view, humans are the most aggressive hominids, perhaps the most aggressive species on the planet, which is why we have come to dominate all the other species.

Man had emerged from the anthropoid background for one reason only: because he was a killer. Long ago, perhaps many millions of years ago, a line of killer apes branched off from the non-aggressive primate background. ... We learned to stand erect in the first place as a necessity of the hunting life. ... And lacking fighting teeth or claws, we took recourse by necessity to the weapon - Robert Ardrey (African Genesis, 1961)

Scene from "2001: A Space Odyssey (1968)", in which the first human tool is a weapon. When the killer ape throws the bone, a million years pass and it becomes a space ship orbiting Earth.

This idea was challenged by Hart & Sussman (2005) in Man the Hunted. They argue that our ancestors were not killer-predators but prey to dangerous animals like sabre-tooth tigers. This meant that humans evolved to survive by cooperating and looking out for one another. Cooperation, not aggression, has driven human evolution.

The film "Ice Age" (2002) makes a very different point, that cooperation and self-sacrifice are the key to survival (you get it that all the animals represent "us", right?)

If the "Killer Ape" theory is true, then war and violence will always be with us. If the "Cooperative Ape" theory is true, then war and violence are the exceptions to the rule that happen when communication breaks down. This will be explored in more detail in the Biological Key Question.

EXEMPLAR ESSAY
How to write a 8-mark answer

Evaluate and apply the Theory of Evolution to aggression. (12 marks)

• A 12-mark “evaluate” question awards 4 marks for describing evolutionary processes leading to aggression (AO1), 4 marks for applying the theory to aggression (AO2) and 4 marks for evaluation (AO2). You need a conclusion to get a mark in the top band (7-8 marks).

Description
Evolutionary theory is based on the idea of descent with modification. Parents pass on characteristics to their offspring and natural selection means that the fittest characteristics survive and become commonplace.
This explains aggression because aggressive behaviour has survival value if it helps a creature defend itself or defend its mate and offspring.
Less aggressive creatures do not survive or protect their offspring, so they do not pass on their non-aggressive genes.
Dart's "Killer Ape Theory" says we are evolved from especially aggressive primates.


Application
Evolution explains sexual jealousy. This is because a sexual rival may pass on his genes instead of your own. Males prevent this by what Buss calls "mate retention strategies".
A certain level of jealous aggression has fitness, but excessive aggression is unattractive to the opposite sex and may lead to domestic violence.
Evolution also explain social aggression, since this carries fewer risks than physical aggression.
Social aggression came about when we evolved to communicate and live in social groups. It enables individuals to be powerful if they are intelligent and manipulative even if they aren't physically strong.


Evaluation
The Theory of Evolution is a respectable scientific theory with a lot of supporting evidence. It underlies the Animal Model, which is the idea we can generalise from animal studies to humans.
However, humans have evolved to be different from other animals; we are self-aware and can make conscious decisions.
Aggression might go against survival if it weakens the group. Group selection argues groups only need some members to be aggressive, not all of them.
The "Killer Ape" theory has been opposed by the "Cooperative Ape" theory which says we evolved to cooperate rather than attack.

Conclusion
Human evolution is partly driven by aggression but partly by the need to cooperate. We therefore have a choice about how to solve our problems and don't have to be "killer apes".

• Notice that for a 12-mark answer you don’t have to include everything about evolution. I haven’t mentioned the brain, testosterone or the role of random mutation. But it is a balanced answer - one third description, one third application and one third evaluation.