A few weeks ago LibriVox published the first volume of David Hume’s “Treatise on Human Nature”, which I promptly picked up as a companion for my winter walks. One of Hume’s most famous claims was that all human ideas and emotions, regardless of complexity, came from experience. While it may seem too extreme to be relevant, this idea is very much alive and kicking in the “nature vs. nurture” debate, and can benefit from Darwin’s notion of natural selection.
Hume’s notion of how ideas are developed from sensory input is very intuitive for simple cases (e.g. how we develop the concept of a color), but takes some work for more complex ones. He claims that even very complicated concepts are just simple ideas put together with some basic operations of the mind. In this way it follows that nothing that we know or think could come from anywhere else but our observation of the outside world.
One implication of this perspective is the notion that a person is born without any prior knowledge at all. Therefore, everything that we learn and the way that we function must be learned from our environment after we are born. Here is where Hume’s hypothesis (originally Locke’s) starts running into trouble.
If you are familiar with the eternal nature vs. nurture debate, you’re probably aware of a number of long-term studies on twins. One of their more famous results is the finding that twins that were raised in vastly different environments are much more similar in personality and behavior than any two randomly selected individuals. Since personality is partially composed of complex ideas, and ideas are supposed to come only from experience, how is it possible that these two individuals are so remarkably alike with such distinct experiences?
In this perspective, Hume’s empiricism clearly leads to a contradiction. If two people are different from each other, then, it must be because they were born different and, in a lesser degree, because they’ve lived differently. If Hume’s notion is to retain any use, it will require some updating.
For the sake of argument, let’s assume an unlikely scenario where these two people had the exact same experiences in life. This leaves us with the genetic differences between them (i.e. the opposite of the twin studies that we discussed). So, where do these genetic differences come from?
Genes are essentially units of information – hereditary blueprints for all living beings. When we say genetic differences, we mean that the instructions in the DNA of each of these two persons will yield different traits as end results. To understand why these different instructions arise, we need to look at Darwin’s concept of natural selection: Essentially, the specific genes or traits that will make up a person are determined by how effective they were in keeping his ascendants alive and healthy in order to have successful children.
The genes that comprise us then do not only carry blueprints of our traits – they carry blueprints of traits that have been shown to be successful in the world for our ancestors. Through natural selection, the genes that get passed on end up relaying information about the nature of the world and the more effective ways to interact with it. Although the way that genes “collect” this information is very different from the way we learn through direct observation of the world, the end result is the same.
To illustrate the point, consider the difference between making a pot out of clay and making one out of stone. You can think of the way we generate ideas and impressions in our everyday lives as making a clay pot – we get impressions and sensations (the clay) from our senses and past experience, and use this input and our mental faculties to generate a more complex idea or concept (the finished pot).
If we want to use stone instead of clay we need to start with a large block and then chip away at it until only our pot is left. This is the way that evolution generates ideas and impressions throughout time. All the possible ideas that could be generated about a particular phenomenon (the block of stone) are filtered through generations by natural selection (the chipping away) until the remaining organisms have the idea that best described how to interact with this phenomenon (the finished stone pot).
A crude example of this natural selection of ideas is people’s aversion to extreme heat. This aversion is essentially an ingrained model – a causal relationship between extreme heat and its effect on our body. Imagine an initial set of people, where a different idea of what the relationship between extreme heat and their body is randomly assigned (i.e. one group believes that it will feel wonderful, one believes that it won’t matter at all, etc.). If we allow time to pass and these people to interact with sources of extreme heat, over a large amount of time we would expect the only survivors to be those who had an accurate model of the relationship.
In comparison to our direct method of observing our environment, this “genetic” observation is slow and limited. As the above example shows, the perfecting of each “model” or idea is a process spanning many generations. Even the end result of the process will be a very crude model, likely to mistake correlation with causation. Finally, the mechanism is also restricted to generating models or ideas only in direct relationship to the human being’s survival and reproduction – for any relationship irrelevant to how we avoid a premature death and acquire food, shelter and a mate, this evolutionary process will likely yield incorrect models or notions (if any at all).
The accumulation of these ideas throughout the generations eventually led to what is now our capacity to directly observe and process empirical stimuli. The relatively new direct method of observation, being much quicker and more powerful than its predecessor, is such a key intellectual faculty that it is easy to see how it could be mistaken for being the sole method of acquiring information available to us. Regardless of our dismissal of this evolutionary acquisition of information about the world as practically useless, it continues silently.
From these findings, we can modify Hume’s notion in the following manner: All traits in a human being come from experience, either directly (through observation in our own lifetime) or indirectly (through the naturally selected information in our genes). While this adaptation of the original may seem to some to be broad to the point of lacking substance, it is consistent with current knowledge and retains Hume’s essential intuition that all human knowledge comes from an empirically observable world.