Skip to content

Constraints on intelligence

by Gideon Kowadlo and David Rawlinson


This article contains some musings on the factors that limit the increase of intelligence as a species.

We speculate that ultimately, our level of intelligence is limited by at least two factors, and possibly a third:

  1. our own cultural development,
  2. physical constraints, and
  3. an intelligence threshold.

We’ll now explore each of these factors.

Cultural Development

Natural Selection

Most readers are familiar with Natural Selection. The best known and dominant mechanism is that fitter biological organisms in a population tend to survive longer, reproduce more frequently and successfully, and pass on their traits to the next generation. Given some form of external pressure and therefore competition, such as resource constraints, the species on average is likely to increase in fitness. In competition with other species, this is necessary for species survival.

Although this is the mechanism we are focusing on in this post, there are other important forms of selection. Two examples are ‘Group Selection’ and ‘Sexual Selection’. Group selection favours traits that benefit the group over the individual, such as altruism. Especially when the group shares common genes. Sexual selection favours traits that improve an individual’s success in reproducing by two means: being attractive to the other gender, and ability to compete with rivals of the same gender. Sometimes sexually appealing characteristics are highly costly or risky to individuals, for example by making them vulnerable to predators.


Another influence on ability to survive is culture. Humans have developed culture, and some form of culture is widely believed to exist in other species such as primates and birds (e.g. Science). Richard Dawkins introduced the concept of memes, cultural entities that evolve in a way that is analogous to genes. The word meme now conjures up funny pictures of cats (see Wired magazine’s article on the re-appropriation of the word meme), and no-one is complaining about that, but it’s hard to argue that these make us fitter as a species. However, it’s clear that cultural evolution, by way of technological progress, can have a significant influence. This could be negative, but is generally a positive, making us more likely to survive as a species.

Culture and Biology

A thought experiment regarding the effect on survival due to natural selection and cultural development, and due to their relationship with each other, is explored with a graph below.

Figure 1: A thought experiment: The shape of survivability vs time, due to cultural evolution, and due to natural selection. The total survivability is the sum of the two. Survivability due to natural selection plateaus when it is surpassed by survivability due to cultural evolution. Survivability due to cultural evolution plateaus when cultural development allows almost everyone in the population to survive.

For humans, the main biological factor contributing to survival is our intellect. The graph shows how our ability to survive steadily improves with time as we evolve naturally. The choice of linear growth is based on the fact that the ‘force’ for genetic change does not increase or decrease as that change occurs*. On the other hand, it is thought that cultural evolution improves our survivability exponentially. In recent years, this has been argued by well known authors and thinkers such as Ray Kurzweil and Eliezer S. Yudkowsky in the context of the Technological Singularity. We build on knowledge continuously, and leverage our technological advances. This enables us to make ever larger steps, as each generation exploits the work of the preceding generations. As Isaac Newton wrote, “If I have seen further it is by standing on the shoulders of giants” **. Many predict that this will result in the ability to create machines that surpass human intelligence. The point at which this occurs is known as the aforementioned Technological Singularity.

Cultural Development – Altruism

Additionally, cultural evolution could include the development of humanitarian and altruistic ideals and behaviour. An environment in which communities care for all their people, which would increase the survivability of (almost) everyone to the threshold of reproduction – leaving only a varied ability to prosper beyond survival. This is shown in the figure above as a plateau in survivability due to cultural evolution.

Cultural Development – Technology

Cultural factors dominate once survivability due to cultural evolution and technological development surpasses that due to natural selection. For example, the advantages given by use of a bow and arrow for hunting, will reduce the competitive advantage of becoming a faster runner. Having a supermarket at the end of your street will render faster running insignificant. The species would no longer evolve biologically through the same process of natural selection. Other forces may still cause biological evolution in extreme cases, such as resistance to new diseases, but this is unlikely to drive the majority of further change. This means that biological evolution of our species would stagnate***. This effect is shown in the graph with the plateau in survivability due to natural selection.

* On a fine scale, this would not be linear and would be affected by many many unpredictable factors such as climate changes, other environmental instability as well as successes/failures of other species.

** Although this metaphor was first recorded in the twelfth century and has been attributed to Bernard of Chartres.

*** Interestingly, removal of selective pressure does not allow species to rest at a given level of fitness. Deleterious mutations rapidly accumulate within the population, giving us a short window of opportunity to learn to control and improve our own genetic heritage.

Physical Constraints

One current perspective in neuroscience, and the basis for our work and this blog, is that much of our intelligence emerges from, very simply put, a hierarchical assembly of regions of identical computational units (cortical columns). As explained in previous posts (here and here), this is physically structured as a sheet of cortex, that form connections from region to region. The connecting regions are conceptually at different levels in the hierarchy. The connections themselves form the bulk of the cortex. We believe that with an increasingly deep hierarchy, the brain is able to represent increasingly abstract and general spatiotemporal concepts, which would play a significant role in increasing intelligence.

The reasoning above predicts that the number of neurons and connections is correlated with intelligence. These neurons and connections have mass and volume and require a blood supply. They cannot increase indefinitely.

Simply increasing the size of the skull has its drawbacks. Maintaining stable temperature becomes more difficult, and structural strength is sacrificed. The body would become disproportionately large to carry around extra mass, making the animal less mobile, coupled with the fact that there would be higher energy demands. Larger distances for neuronal connections leads to slower signal propagation which could also have negative impact. Evidence of the consequences of such physical constraints is found in the fact that the brain folds in on itself, appearing wrinkled, in order to maximise surface area (and hence the number of neurons and connections) in the given volume of the skull. Evolution has produced a tradeoff between these characteristics that limits our intelligence to promote survival.

It is possible to imagine completely different architectures that might circumvent these limitations. Perhaps a neural network distributed throughout the body, such as exists for some marine creatures. However, it is implausible that physical constraints would not ultimately be a limiting factor. Also, reality is more constrained than our imagination. For example, it must be physically and biologically possible for the organism to develop from a single cell to a neonate, and on to a reproducing adult.

An Intelligence Threshold

There could be a point at which the species crosses an intelligence threshold, beyond which higher intelligence does not confer a greater ability to survive. However, since the threshold may be dictated by cultural evolution it is very difficult to separate the two. For example, the threshold might be very low in an altruistic world, and it is possible to envision a hyper-competitive and adversarial culture in which the opposite is true.

But perhaps a threshold exists as a result of a fundamental quality of intelligence, completely independent of culture. Could it be, that once you can grasp concepts at a sufficient level of abstraction, and have the ability to externalise and record concepts with written symbols (thereby extending the hierarchy outside of the physical brain), that it would be possible to conduct any ‘thought’ computation, given enough working memory, concentration and time? Similarly, a Turing Machine is capable of carrying out any computation, given infinite memory.

The topic of consciousness and it’s definition is beyond the scope of this post. However, accepting that there appears to be a clear relationship between intelligence and what most people understand as consciousness, this ‘Intelligence Threshold’ has implications for consciousness itself. It is interesting to ponder the threshold as having a corresponding crossing point in terms of conscious experience.

We may explore the existence and nature of this potential threshold in greater detail in the future.

Impact of Artificial General Intelligence (AGI)

The biological limitations to intelligence discussed in this article show why Artificial General Intelligence (AGI) will be such a dramatic development. We still exist in a physical world (at least perceptibly), but building an agent out of silicon (or other materials in the future), will effectively free us from all of these constraints. It also allows us to modify parameters, architecture and monitor activity. It will be possible to invest large quantities of energy into ‘thinking’ in a mind that does not fatigue. Perhaps this is a key enabling technology on the path to the Singularity.

0 thoughts on “Constraints on intelligence”

Leave a Reply