In the previous lectures, we have seen that all biological organisms, from bacteria to humans, have to cope with a world that is complex and often inpredictable. All organisms have mechanisms to respond to the information from the world around them. For example, bacteria can detect concentrations of chemicals around them and then change their movement pattern to move towards a higher concentration of that chemical. You can see this as a very simple form of decision making. Human decision making is, of course, much more elaborate. We have the unique capability to imagine what the consequences of our actions could be and act according to that.
Our decision making behaviour is influenced by many factors, such as the culture that we grew up in and earlier experiences that we’ve had in life. But like in all animals, human decision making is also partly driven by natural instincts that we are often not even aware of.
Decision making mechanisms that we observe in the biological world are the result of biological evolution. Because of natural selection, genes that cause organisms to be able to survive and leave many offspring will become common in a population. So if there are genes that cause organisms to take decisions in such a way that these organisms produce many offspring, these genes will spread in the population and the associated decision making behaviour will become common. This way, natural selection has shaped decision making behaviour in natural populations. But natural selection can do strange things. When you look around in the animal kingdom, including humans, you often see decisions that seem illogical or even stupid.
For example, the cuckoo bird famously lays its eggs in the nests of other birds. The other bird then takes care of the cuckoo chick, even though it looks very different from its own young. This seems like a strange decision. Why does the other bird not decide to refuse to feed the cuckoo chick or to abandon the nest? In humans, we also see that people have all kinds of cognitive biases that make them process information and make decisions in a way that is not rational. An example is the anchoring effect, which was famously shown in an experiment with German judges. These judges were told a fictional story about somebody who had been caught shoplifting.
Next, they were instructed to roll a die that always landed on either a three or a nine. They were first asked if they would give a longer prison sentence in months than the number they had rolled or a shorter one. Then they were asked how long the exact sentence was that they would give. Judges that rolled a three, on average, give a sentence of five months. And judges that rolled a nine, on average, gave a sentence of eight months. So why do animals and human beings often completely disregard important information, like the bird that feeds a cuckoo young that looks completely different from its own young?
And on the other hand, why are they often influenced by clearly irrelevant information in their decision making, like the judges? The reason is that natural selection does not produce perfect decision makers. This is partly because the world is too complex. Animals face many different circumstances and almost never are two situations exactly the same. Decision making mechanisms which are controlled by the neurological and physiological machinery of the individual are not infinitely flexible. It is impossible for natural selection to shape decision making mechanisms so that they have the perfect answer to every possible situation that the organism may face. Decision making mechanisms are more like rules of thumb, or heuristics.
They perform relatively well on average, but they can be suboptimal in specific situations. And they can even produce major errors under nonstandard circumstances. A bird that is taking care of a cuckoo young is making a decision to feed a hungry mouth in its nest. In the vast majority of cases, that decision is good for the reproductive success of that bird. But on some rare occasions when there is a cuckoo chick in the nest, it is a bad decision. But on average, feeding a hungry mouth in your own nest is a good decision.
Another important reason why natural selection can produce behaviour that seems suboptimal is that natural selection does not necessarily work in the best interests of the individual. Natural selection works in the interest of genes. So you can see individuals as temporary vehicles that behave in the best interest of the genes that they are carrying. To see this, consider a bee colony. In a bee colony, there is only one reproducing individual, the queen. The worker bees in the colony never reproduce, but do often risk their lives to protect the queen. They have zero reproductive success, so they do not act in their own interest, but they act in the interest of the genes that they carry.
Because the workers are related to the queen, they have many genes in common with her. So if a worker acts to protect the queen, they indirectly help their own genes to be transmitted to the next generation.
Thinking in terms of the long-term persistence of genes, rather than the survival and reproduction of individuals, help us understand why behaviour often seems suboptimal from an individual point of view. An example is risk taking behaviour. Let’s do a thought experiment. Consider an organism that lives in a climate that is dry in some years and wet in others. Each individual lives for one year, reproduces, and then dies. Every year, there is a 50-50 chance that the year will be wet or dry. Now let’s consider two strategies, a low risk strategy that can perform relatively well in both wet and dry years, but never does exceptionally well. Let’s assume that those individuals always have two offspring in both wet and dry years.
And the other strategy is a high risk strategy. It has adapted very well to the dry climate, but does not do so well in wet climate. So if the climate is dry, this strategy has three offspring. But if the climate is wet, it has only one. Now for an individual, both strategies are, in principle, equally productive. Both high risk individuals and low risk individuals will have, on average, two offspring. But for natural selection, the strategies are not equivalent. You can see how that works in this animation. We look at four years, two of them wet and two of them dry. We start with one low risk individual on the left and one high risk individual on the right.
The first year is a dry year, so the low risk individual has two offspring and the high risk individual has three. The next year is wet, so all low risk individuals again have two offspring, but all high risk individuals have only one. If we add one more dry year and then one more wet year, you see that the low risk individuals are starting to outnumber the high risk individuals. Even though both strategies are equally productive from an individual point of view, natural selection is favouring the low risk strategy, which will become more and more common than the high risk strategy. So this example shows you why you may sometimes see adaptations that are not necessarily optimal for the individual.
In conclusion, human decision making is based on mechanisms that are the product of natural selection. These mechanisms have strong limitations, which explain why decision making can often be suboptimal. In addition, our decision making mechanisms did not evolve to benefit us but to benefit our genes. Therefore, they can produce systematic biases. Being aware of those biases and understanding how evolution has shaped them can perhaps help us in seeing our own weaknesses and being able to deal with them better while making decisions in a complex world.