What makes us exceptional?

New research could throw some light on the unique evolution of the human brain.

Sandy Starr

Topics Science & Tech

A new scientific study claims that genes controlling the size and complexity of the brain have evolved more rapidly in humans than they have in any other species – including apes.

Bruce Lahn, a geneticist at the Howard Hughes Medical Institute at the University of Chicago and one of the principal authors of the study, argues that ‘people in many fields…have long debated whether the evolution of the human brain was a special event’. According to Lahn, ‘our study settles this question by showing that it was’ (1).

These claims form part of a well-established trend, in which diverse aspects of human intelligence and behaviour are attributed to biological causes. The burgeoning field of genetics in particular has provided the occasion for explaining away many a human characteristic, in terms of the composition of our DNA. This in turn has fuelled the interminable nature-nurture debate, and competing arguments that either our biology or our upbringing ultimately account for the way in which we think.

The latest study, published in the journal Cell, investigates the evolutionary development of 214 genes. Researchers compared the development of these genes in four different species: humans, macaque monkeys, rats and mice. Contrary to earlier assertions derived from genetic studies, the researchers in this instance argue that there is a genetic basis for – rather than against – humans being exceptional: ‘The remarkable phenotypic evolution of the human nervous system has a salient molecular correlate, ie, accelerated evolution of the underlying genes.’ (2)

The biological similarity between humans and other primates, such as apes, is often assumed to be self-evident, leaving those who would argue against human exceptionalism to try to find behavioural similarities that might strengthen their case (see Why humans are superior to apes, by Helene Guldberg). But Lahn claims that the human brain is actually ‘far more complicated in terms of structure’ than that of the macaque monkey.

According to Lahn, the new study offers evidence for the genetic underpinning of human intelligence. Apparently, ‘the evolution of the human brain probably involves hundreds if not thousands of mutations in perhaps hundreds or thousands of genes – and that is a conservative estimate’ (3). These mutations are believed to have occurred over 20 to 25million years, which would make human evolution unusually rapid, compared with what we know of the evolution of other species.

While this data is interesting, we should be careful not to overestimate what it can tell us about human faculties as a whole – because these faculties are not rigidly circumscribed by our genetic makeup or our evolutionary past. Over the course of human history, we have been successful in cultivating our faculties, shaping our development, and impacting upon the wider world in a deliberate fashion, quite distinct from evolutionary processes. While evolution by genetic mutation and natural selection can be shown to follow certain patterns, this process lacks the capacity of human society to formulate specific and conscious goals.

This unique human ability was forgotten by many, following the recent completion of the Human Genome Project to identify and determine the sequences of all of the genes in human DNA. When it was discovered that humans possess far fewer genes than was previously thought, this was interpreted as evidence that humans are not all that different from non-humans.

The latest discoveries about our biological evolution, by Lahn and his colleagues, appear to point to the opposite conclusion, confirming rather than denying human exceptionalism. Even so, it would be a mistake to assume that these discoveries can explain what makes us exceptional.

As Kenan Malik, author of Man, Beast and Zombie: What Science Can and Cannot Tell Us About Human Nature, argues: ‘We are biological beings, and under the purview of biological and physical laws. But we are also conscious beings with purpose and agency, traits the possession of which allow us to design ways of breaking the constraints of biological and physical laws.’ (4) Our biological evolution provides necessary, but insufficient, conditions for our further development through society.

The exciting thing about the latest insights into our biological development is that, coupled with an understanding of our social development, we might better understand how the latter came to supersede the former. Lahn himself acknowledges that ‘we have to start thinking about how social structures and cultural behaviours in the lineage leading to humans differed from that in other lineages’ (5). Since our humanity consists in more than our biology, biology alone cannot account for how we came to be human.

Read on:

Why humans are superior to apes, by Helene Guldberg

Genes, culture and human freedom, by Kenan Malik

spiked-issue: Genetics

(1) Human brain evolution was a ‘special event’ (.pdf 78.6 KB), Howard Hughes Medical Institute, 29 December 2004, p1

(2) Abstract, ‘Accelerated evolution of nervous system genes in the origin of Homo sapiens‘, Jeffrey Anderson, Steve Dorus, Patrick Evans, Sandra Gilbert, Bruce Lahn, Michael Mahowald, Christine Malcom, Eric Vallender, and Gerald Wyckoff, Cell, 29 December 2004

(3) Human brain evolution was a ‘special event’ (.pdf 78.6 KB), Howard Hughes Medical Institute, 29 December 2004, p2, 4

(4) Genes, culture and human freedom, by Kenan Malik

(5) Human brain evolution was a ‘special event’ (.pdf 78.6 KB), Howard Hughes Medical Institute, 29 December 2004, p4

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Topics Science & Tech


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