Evolution, Culture and Human Nature

Why are our decisions often guided by emotions even though rationally we ‘know’ better? Evolutionary origin of the conflict between our emotional and rational brain

The relationship between emotions and rationality has been a curiosity to the human species for centuries. Many people believe that emotions are a by-product that inhibits our ability to make correct decisions and to think rationally. These people would think that Spock from Star Trek (Roddenberry, 1966), as he is Vulcan – a species that suppresses their emotions in order to act more rationally – is an ideal we would do well to strive for. Spock lives up to the philosophy of his kind and hence is an emotionless character aboard the ship. This converts him to a highly logical companion which is why the captain likes having him around.

An opposite of this is seen in Marvin the Paranoid Android from Hitchhikers Guide to the Galaxy (Adams, 1979) who is a robot, so he is rational. However he was fitted with a GPP (Genuine People Personality) which included emotions. This then transformed him into a heavily depressive machine who was incapable of doing many tasks due to this emotion. These two examples show that this idea of emotions being ‘irrational’ is quite ingrained in popular culture. Yet how could something which causes such a hindrance to our problem-solving have possibly evolved? If this relationship between emotions and rationality is true then surely other hominoids would have had higher reproductive fitness as they could make sensible decision without the drawback of emotions. So why did we prosper and not they? Could evolution really create something that is such a handicap?

How could emotions evolve?

Firstly evolution does not aim to create perfection. For instance the urethra of a male goes through the prostate gland rather than around it which causes problems for the person later in life, the eye has a blind spot because of the way it is wired up and many people will suffer from back pain due to the way the back is formed (Ainsworth and Le Page, 2007).  This is because evolution’s aim is not to make organisms faultless, its aim is to adapt that organism to its environment given what physical attributes that organism already has or mutates. Hence this is often the reason why we do not always see perfection around us. It is because evolution builds on what was there before. The giraffe’s laryngeal nerve (which stimulates the voice box) rather than passing directly between the larynx and the brain instead goes all the way down the neck, loops round an artery near the heart and goes all the way back up again. If evolution was a perfectionist it would have gone straight from the brain to the larynx. The reason for this peculiar route is because, for the giraffe’s fish ancestors, going around this artery was the most direct route where it linked the brain to the gills. Then as it evolved and gained a mammalian neck, this connection grew longer and longer as it was always easier and more likely for the animal to mutate a longer laryngeal nerve than mutate a more direct connection. Humans possess the same nerve which also runs down from our brain towards our heart before turning round to come back up the neck and finish at the larynx, very close to where it started (Dawkins, 2009).

In this case perhaps humans could have evolved emotions even though they appear to be a hindrance. However the difference between these two examples is that one is about physical traits and one psychological. Descartes mind-body dualism philosophy proposes that the mind can affect the body but the body cannot affect the mind. If this was true then evolutionary processes could not occur on the mind, hence no evolution of emotions. However today we also know that our minds are products of physical things and physical events, for instance pain is a psychological phenomenon triggered by the body.  From this we can conclude that evolution can occur on psychological functions, since the brain is the intermediary between the mind and the body.  For example stimulation of the motor strip can cause body parts to twitch and stimulation of the sensory cortex can cause a sensation to be felt in body parts (Penfield and Boldrey, 1937). Therefore mutations of wiring in the brain can cause differences in the phenotype which can be selected for through natural selection. The mind can evolve.

Without emotions are we rational?

An easy way to solve this rational vs irrational problem would be to take a person and remove all their emotions and see what barriers to survival this makes. Ethically you could not do this, but with case studies of people with brain damage we can come close. Damasio (1994) talks about his favourite patient, known as Elliott, who had suffered damage to his orbitofrontal cortex.  This area of the brain receives extensive sensory input from all modalities (visual, auditory, somatosensory and gustatory) and gives output to the limbic system which contains brain parts such as the amygdala which, is important for emotional expression (Camille et al., 2004).  It also sends input to the medial temporal lobe which means it is useful in processing emotionally salient stimuli (Rempel-Clower, 2007). Thus the orbitofrontal cortex is at the interface of emotion and cognition in the brain.

Elliott had a high IQ and also had high accuracy in tasks involving cognitive flexibility, such as card sorting and mental calculations (Levine, 1998). However he was lacking in normal emotional responses to everyday situations, for instance he was unusually calm in the face of misfortune. His high cognitive flexibility suggests he has all the cognitive mechanisms to make a decision, but importantly for this essay, he was actually a poor decision maker. An anecdote is told where Elliott was asked to choose a restaurant to go to. Elliott then proceeded to visit every restaurant, read all the menus and generally collect all information he could on each one. However he was unable to make the decision of which one to eat at even though he had all the information available.  This inability to make decisions also lead to him losing his job.

Damasio’s case study obviously shatters the idea that emotion and rationality are opposites as Elliott was capable of rational thought, yet without emotions he was incapable of making any decision. He, like Spock, should have been able to make only wise and rational choices, yet with this evidence it seems common sense that good decision making needs emotions. A person needs emotional investment in outcomes of the decision and as Elliott lacks these he has no basis on which to decide. It is also obvious that Spock must have some emotions as otherwise he would not have the motivation to rise to his rank or other emotions such as loyalty and curiosity, i.e. he would have no reason to get up in the morning. This even comes across in the show;

Kirk: Have I ever mentioned you play a very irritating game of chess, Mr. Spock?

Spock: Irritating? [smiling] Ah, yes. One of your Earth emotions.” – (Peeples, 1966)

The most obvious thing from this quote is that he smiles and Spock cannot do this without the underlying emotion of happiness. He must also have interest in wanting to play the game and disapproval in Kirk’s “Earth emotions”. Damasio (1994) concludes that effective decision making not only isn’t hampered by emotion; it requires emotion.

Do other animals have emotions?

From an evolutionary perspective not having any emotions is a huge barrier to fitness. A key factor to this would be that you would not be able to select a mate and if you cannot do this then how is your species to create the next generation? It cannot.

Logically therefore the same must also apply in animals other than humans. Yet there are many animals that seem to survive on pure instinct (“an innate, typically fixed pattern of behaviour in animals in response to certain stimuli” (instinct, (n.d.)). However such animals do not appear to act rationally i.e. moths are attracted towards flames which would kill them and flies perpetually fly into a window trying to escape outside and can die of exhaustion. This means they use the stimulus-response mechanism for survival. This does have some benefit i.e. instantaneous response to movement. It would appear that these types of animals do not have emotions as we do. So then why do we possess this trait when we do not need it for survival fitness?

Observation suggests that creatures that appear to have emotions are social animals; e.g. elephants are known to mourn the loss of a member of their herd. This could be because a group is not able to survive if all its members act on pure instinct, i.e. you cannot have cooperation. There are two solutions to this problem, one is to become a super-organism i.e. a colony of ants or bees where the entire colony acts as one organism with individual members giving their lives for the colony. This only works when all members of the group are very closely related. This means that even if they sacrifice themselves for the benefit of the group their genes will still be passed on to the next generation.

The other is a group where its members have greater variation in the collective genetic pool. This sort of group cannot survive using the same methodology as a super-organism. A member would not be as likely to sacrifice itself as its genes would not be passed on. Hence they must rely on something else. Such animals appear to have emotions.

A reason for this might be that emotions help members take decisions that benefit the group. Emotions allow for a pause between stimulus and response where the animal can consider its options and choose how to act. Their behaviour is not fixed, though it may have a preferred outcome. Emotions are a signal for the animal to make a decision; they can stop, consider their options and make the most rational choice. The pause allows them to take the most rational decision based on the needs of the group, themselves and previous experience. This gives them the ability to learn through trial and error.

Kohler (1925) showed this in an experiment where he put a dog in a three sided box and then placed some food on the other side (Image 1). Instinct tells the dog to move towards the food (Route A). However eventually, with the help of the appearing emotion of frustration, the dog learns to disregard this instinct and take the rational choice to move away from the food and go round the edge of the box to obtain it (Route B). If the dog ran only on instinct he would just move towards the food, the dog would see the stimulus, food, and respond by approaching.  However it would not manage to get to it, this would be very irrational. Dogs in the wild (wolves) live in packs and hence are social creatures. Many owners of dogs would say they have emotions such as sadness when pining for food. So it is likely that they evolved emotions to benefit group dynamics and this ability allows them to solve Kohler’s barrier task. This essay would hypothesize that animals that work via instinct would not be able to solve this puzzle as they would keep trying to take Route A like the fly trying to escape through a closed window. Emotions give us the option to make rational choices and learn through trial and error so our social group can survive.


How are emotions represented in the brain?

Another line of evidence to support this theory is to do with the old and older brain in species.  The limbic system is often referred to as the old brain, but there is an older part, the reptilian brain (Image 2). This part (which contains mostly the basal ganglia) deals with our vital functions (heart rate, breathing, body temperature etc.) and instincts such as fight, flight or freeze (Goleman, 1996). As suggested by the name our reptilian brain shares similar anatomy to reptiles who are not social creatures and hence run only on instinct. Yet this system also occurs in avian brains and exists within all vertebrates and hence is likely to date to the common evolutionary ancestor of the vertebrate.

Image 2: The Evolution-Designed Brain (Macdonald, 2010).

When mammals evolved new parts of the brain evolved around the reptilian brain too, the limbic system. This part deals with less instinctive emotions such as anger and dread. The animals were now able to compare new smells with old ones and decide what to do about it (Goleman, 1996). This part of the brain also specifically mediates the social emotions such as separation distress/social bonding, playfulness and maternal nurturance (Panksepp, 1998). Hence the trait of emotions was built upon those of instinct and lead towards creatures becoming more social. It allowed for cooperation (Badger, 2012).

Upon this system “newer mammals” such as primates evolved a neo-cortex. This allowed them to have even more complex emotions and advanced planning (such as planning an attack on a neighbouring troop) (MacLean, 1990). This “extra brain” generally allows for high cognitive functions to take place and can be seen in the difference in behaviour between cats and dogs and our own.  Animals with a neo-cortex, with their increase in complexity of emotions, have a predisposition to live in groups. In fact the size of group that primates live in is highly correlated to the size of their neo-cortex (Dunbar, 1992) and sociality in general is the best behavioural measure to correlate with brain size across species (Schoenemann, 2006).

This idea of three brains established by MacLean (1990) and his triune brain hypothesis shows that as mammals evolved their brains were able to use more and more complex emotions to aid them in day to day life. It allowed them to be able to learn from past mistakes and to question their instincts. They could make a choice whether to ignore them or to do something about them. Emotions were a signal to make a decision and gave them the ability to change their behaviour in a situation and not to always act in a specific way. It allowed for an extra step to be made in the stimulus-response reaction. Now the situation went stimulus-decision-response. These meant animals were more likely to be able to work together without the need for a ‘queen role’ as in super-organisms. They now did not need someone at the top who produced hormones that tell them what to do. They can now make decisions for themselves. This made them more likely to be able to live in social groups as they could be formed more spontaneously, by essentially any member and also allowed for movement between groups. This increases their chances of survival as if a bee colony does not have a queen then the whole colony dies. For animals with a limbic system their emotions now guide them, fear keeps danger at arm’s length, love means we can protect our relatives and grief shows us what happens if we don’t (Badger, 2012).

Why are we irrational?: Biology

The question remains though, if emotions evolved to help us make rational decisions then why do we assume they are so irrational? The main reason for this is that the world we live in today is very different from the one our ancestors evolved these processes in. Hence our emotions can cause reactions to things that made sense in the past, but now are not appropriate.

A majority of this irrational behaviour occurs when strong emotions are involved such as fear. This is because our brain uses two routes to deal with stimuli. Sensory input is sent to the hypothalamus in the limbic system that then sends this data to both the neo-cortex for detailed, but slow, evaluation and also to the reptilian brain which makes a more rough and ready yet immediate decision. If the reptilian brain senses danger then it puts the brain into crisis mode and activates the instinctual fight, flight or freeze response, while the emotion of fear is being processed by the neo-cortex. This immediate reaction, however, then leads to an immediate response from the person before the neo-cortex has had time to make its own sophisticated decision about the situation (MacDonald, 2010).

Hence a person who feels anger and jealousy because he sees his girlfriend talking to another man will activate this crisis mode. The man will then instinctually fight and will end up hitting the other man, before the more rational neo-cortex tells him that the two could just be chatting and that the other man was not trying to flirt with her i.e. there is no need to fight. Once the act had occurred the neo-cortex has had time to tell the man that hitting the other man was irrational and so he feels a sense of regret. However he still had the conscious feeling of anger and so he attributes the irrational behaviour to this emotion and not to the unconscious reaction of the reptilian brain.

This response however was very reasonable to our ancestors. For instance when confronting a large predator like a lion, it would be useful to them to have this rapid reaction at their disposal so they could flee quickly or decided to kill and eat the lion. If they relied solely on their neo-cortex in this situation they might have been killed by the lion before they ever reached a decision on what to do. The remains of this system therefore play out in our modern lives, not always for the best. Due to this people have had to increase their emotional intelligence and try to prevent this instinctually action from taking over. However some do not, and have not learned that emotional feelings are simple messages from the limbic system to the conscious mind that are to be ignored or implemented as other brain processes (intellect and intuition) dictate (MacDonald, 2010).

Why are we irrational?: Manipulation

Another way emotions are seen to be irrational is that others can manipulate them and hence get us to react in ways that we do not necessarily want to do. The media is a very good source of this manipulation as they are able to tap into another evolutionary adaption, the availability heuristic, in order to get us to fear things that based on statistical investigation are irrational to fear. The availability heuristic is something that we use to estimate the probability of an event occurring. The way we do this is to think of how many recent occurrences of this event we can think of and then base our probability prediction on this. If we have encountered or heard of this event recently then we think it is highly likely to occur again.

For example the newspapers often report when a plane has crashed or had a major accident which makes them easy to remember. This includes the terrorist attack on the twin towers in 2001. This event made people scared of flying in an aeroplane and instead they chose to drive. Yet to fly in a plane was and is a lot safer than driving by car and the result was unnecessary road deaths (Sutherland, 1992). Hence people’s decision to take the car based on fear was irrational and they put their lives more at risk. Due to the media and other sources, repeated and wide spread reporting of rare events (plane crashes) has led to people overestimating the likely hood that they happen compared to more mundane events (car crash).

Again this coupling of fear, emotion and the availability heuristic evolutionarily makes sense. When we just had members of our tribe around us, if we were to hear that puff adders had killed many people and were very dangerous recently then this would be useful. Thus when we next went out on a hunting trip we would be extra vigilant of the puff adders and may even take alternate paths to avoid them. However with the media and information constantly being given to us from many different places we do not have the ability to validate whether the event being describe is novel or not and so we give them all equal value. This leads to the availability bias of giving high probability to more mentally available events and this creates the irrational behaviour.

Why are we irrational?: The arts

The behaviour mentioned above convinces most people that emotions could be rational, but what about more controversial rationality issues. Are the arts rational? No one would deny that the arts produce emotions, but can we say these emotional feelings are rational? People would argue that when you are in the cinema and you see a vampire and feel fear it is very irrational. Firstly you know that anything you are seeing is not real, especially as there are almost no signs that vampires exist in reality. Secondly the behaviour that accompanies this emotion is not rational. Fear should initiate the fight, flight or freeze system, yet many in this situation move closer to the person they are with. How does this increase our evolutionary fitness?

Dissanayake (1992) suggests that the fact art evokes any emotion means it useful to us and would increase our survival. Evolution would make it that way, for anything that we feel strong emotion for must have some benefit, as what we do not care about we neither pay attention to nor remember. She goes on to propose that art is a behaviour which she calls “making special” (Dissanayake, 1999). All art can be seen as making ordinary behaviour special, but so can other behaviours such as ritual and play. These two behaviours have been found to hold an evolutionary advantage. Hence as art shares similar features with these behaviours, similar selective value has been suggested for it. So perhaps art is rational as it is an extension of making special behaviour which improves our fitness. Though exactly how is not currently understood.

Others suggest that the reason we think this emotion is irrational is to do with a paradox, the paradox of fiction. It is a paradox as individually all points seem to be plausible but together seem to be inconsistent (Feagin, 2009).

  1. “Particular types of emotions require one’s having particular sorts of liefs[sic]. E.g. if I am afraid I must believe I am in danger.
  2. Unless one’s beliefs are justified they must be irrational
  3. Belief’s acquired through reading fiction are unjustified” (Feagin, 2009 p. 32)

This paradox leaves us with either; the emotions we are feeling are irrational or the emotions we are feeling are somehow not the same as emotions when the situation isn’t fictional, they are lesser quasi-emotions. The main proposal to solving this paradox is with “thought theory”. This basically changes the fact that you believe the emotions are real to only imagining they are real. Imagining is seen as neither rational nor irrational, i.e.  it’s non-rational. In other words thought theory concludes that emotions do not require beliefs. Again this idea does not fully explain why we have these emotional reactions to the arts.

With the above two perspectives in mind this debate cannot be solved in this essay, especially as arguments for the arts rationality and evolutionary significance are very vague. Plus there is little literature on the subject, yet this seems strange as the question would seem an often debated subject seeing that scientists would say that spending $1,000 on a painting would be irrational, whilst philosophers argue that emotions in the arts are rational and as such are a big part of our humanity.


Emotions and rationality are clearly not opposites. In fact they are two sides of the same coin; you need emotions in order to be able to make a rational decision and emotions developed in order for animals to be able to make rational choices for the sake of their social group. If you do not have these emotions then you are still able to flourish, but then you are only acting on instinct.

For cooperation you either need to give up your evolutionary fitness and become part of super-organism or feel emotions. Emotions are like a warning system, which tells you when a decision has to be made. The animal is now able to stop and decide what to do, this makes them able to consider others and do what’s best and rational rather than what is automatic.  This then gives the group more chances of being able to work together, surviving and passing on their genes.

However if you do not have emotions then you have not lost your instincts. Emotions are just an extra module fitted to the brain. This is useful in times such as when touching a hot surface, but can also cause situations that are irrational such as unnecessary fighting.

So even though emotions are not irrational they do not make us rational either. We can still be manipulated and they can still be evoked in situations where we are undecided whether the emotions are rational or not. Furthermore emotions can actually make us irrational. The case of Marvin the Paranoid Android is not solely fictional.  Too much emotion can damage us psychologically and make us act irrationally such as with manic depressives and anxiety disorders. Overall emotions give us the ability to be rational, but that does not mean we are always rational.


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