Camilo J. Cela-Conde1
This conference on "Neurobiology of Human Values," organised by the Fondation Ipsen, focuses on some very important aspects of the ever-controversial relationships between what we call "mind" and the brain. The title of its first session, "From aesthetics to ethics," expresses in itself the aim of reaching the core components of the human evaluative capacity.
Let me start with some assumptions that, due to the lack of space, I cannot explain in detail. I am sure thex will be easily accepted by readers interested in the neurobiology of values. First, moral and aesthetic judgements are functional states of the brain's activity. Nowadays, this is a very common way to conceive mental activity. Second, the existence and evolution of ethics - and aesthetics - might be better understood if we could identify the neural networks involved in moral and aesthetic judgements.
However, these assumptions pose some philosophical difficulties. Aesthetics and ethics embody an important part of human nature developed through phy-logeny as a result of evolution by natural selection. On the other hand, the fields of ethics and aesthetics include ethical values and aesthetic preferences. What does that mean? Are these values also the result of evolution? Does human nature include the content of ethics and aesthetics, I mean, ethical and aesthetic values too?
To link genetic components and human values is a forbidden operation, given that it leads to the so-called naturalistic fallacy, formulated by David Hume. That is, if we deduce values from facts, we are making a logical mistake. Let me quote how Joshua Greene, who participates in this conference, expresses this advice: "There is a sharp and crucial distinction between the 'is' of science and the 'ought' of ethics" (Greene 2003). However, in the same paragraph, Greene points out that scientific statements could help us to re-evaluate our concepts of morality. To what extent are those statements helpful? And, particularly, how far should we re-evaluate our conceptions of morality to accept this kind of help?
In spite of philosophers' reluctance to accept values as a natural phenomenon, let us consider the following list of social regularities that are present in many non-human primates: food sharing, reciprocity of alliances, mutual assistance, retributive justice, reconciliation, consolation and conflict mediation.
1 Laboratory of Human Systematics, University of the Balearic Islands, 7071 Palma de Mallorca, Spain; e-mail: [email protected]
These behavioural traits could be considered, in Jessica Flack and Frans de Waal's (2000) opinion, as a sense of social regularity anticipating the human "moral sense."
Flack and de Waal's evolutionary sketch of the human capacities for moral judgment is not scientific nonsense lacking philosophical background. The Scottish Enlightenment understood that the "moral sense" was the element that, based on sympathy, leads human ethical choice. In his account of the evolution of cooperative behaviour, Darwin (1871) stated that any animal whatsoever, with well-defined social instincts - like parental and filial affections - "would inevitably acquire a moral sense or conscience, as soon as its intellectual powers had become as well, or nearly as well developed, as in man" (Descent of Man, p. 472). However, this is a hypothetical issue: no animal has ever reached the level of human mental faculties, language included. In fact, Darwin points out that, even if some animal could achieve a human-equivalent degree of development of its intellectual faculties, we could not conclude that it would also acquire exactly the same moral sense as ours (Descent of Man, p. 473). Therefore, human moral behaviour is a product of natural selection, but it is humankind's exclusive attribute.
The final step towards human values would have hypothetically been reached in our own species, by means of some cerebral modifications fixed through phylogenesis. As Terrence Deacon (1997) held, higher cognitive capacities would have evolved in our own species due to an enlargement of the prefrontal cortex. Thus, the cortical expansion responsible for developing values should have occurred after the cladistic episode that separated human and Neandertal lineages, that is to say, about 700,000 years ago. Actually, we have some items of evidence ofhigh cognitive behaviour in the ancient burials of modern human beings. The burials are, in themselves, proof of the existence of ethical beliefs at that time, from the Upper Palaeolithic to the Neolithic. However, some decorative objects, such as necklaces and colour pigments, suggest the existence of an aesthetical sense too.
What had happened to the human brain by that time? Katherine Semendeferi and Hanna Damasio (2000) proved that no extra-allometric expansion exists in the frontal area of humans. In relative terms, we have the same parieto-occipital, temporal and frontal volumes corresponding to any ape. Only the overall large capacity of our brain makes a volumetric difference. However, the human brain is not just bigger than that of any other simian. Let us consider the cortical gyrifica-tion, measured by tracing an inner contour of the complete surface of the brain and by tracing an outer contour with tangential lines connecting the crests of gyral curvatures of the cortex. James Rilling and Thomas Insel (1999) studied the gyrification index of the primate cortex, showing that gyrification is allometric; the bigger the brain is, the more gyrificated the cortex is. However, an extra-al-lometric gyrification does exist, precisely in the prefrontal cortex ofhumans.
Could there be a relationship between the changes of the human frontal brain areas and the emergence of values? Since the proposal of the somatic marker hypothesis (Damasio 1994), a variety of articles confirmed the existence of a circuit linking the prefrontal and medial temporal lobes (Adolphs et al. 1998, Bechara et al. 2000; Moll et al. 2002; Keightley et al. 2003), that is, a network that is activated during moral judgments. As many of the participants at our conference will maintain, neuroimaging techniques can be used to localise some of these networks. However, what to say about aesthetics? Does the frontal cortex have any role in the human sense of aesthetics?
Our research team tried to answer this question by means of an experiment of localisation of aesthetic perception, carried out using magnetoencephalography (MEG). MEG is a type of brain imaging technique that measures the magnetic fields created by post-synaptic potentials. It has some important advantages: it is a non-invasive procedure, and it has very high temporal resolution and good spatial resolution combined with magnetic resonance (Cela-Conde et al. 2004).
In our experiment, eight female participants successively looked at a great number of pictures (320), deciding whether each picture was "beautiful" or not. Thus, participants themselves fixed the final aesthetic condition of every stimulus. High art pictures, both realistic and abstract, decorative pictures, and photographs of urban and natural landscapes - that is, highly varied material - were used as stimuli.
The results of our experiment show that the left prefrontal dorsolateral cortex (PDC) was greatly activated when participants perceived beautiful stimuli (either natural or artistic), reaching statistically significant differences (see Fig. 1). It is interesting to note that this differential activation took place at latencies ranging from 400 milliseconds to one second. We thus know that the frontal cortex is also activated in the perception of aesthetic pictures. However, we still have not studied the potential existence of invariants, that is, "universals," that could act as items of evidence of the evolutionary fixing of some aesthetic values. So, let's go back to the moral issue.
As Alan Sanfey and collaborators (2003) reported, the prefrontal dorsolateral cortex is activated in a task of evaluating fair and unfair exchanges, such as the so-called "Ultimatum game." Dominique de Quervain and collaborators (2004) also reported that the ventromedial prefrontal cortex and the medial orbitofron-tal cortex are also activated when trying to integrate the benefits and costs of punishing selfish members of the group. On the grounds of both Sanfe/s and de Quervain's experiments, it could be said that the value of fairness depends on the particular circuitry of certain neural networks in our brains. However, we are not the only primates with a sense of fairness. A similar criterion seems to be followed by the brown capuchin monkey, Cebus apella, which also return help in obtaining food (de Waal and Berger 2000) and reject an exchange of tokens for food in unequal conditions (Brosnan and de Waal 2003). Thus, capuchin monkeys are likely to have a sense of fairness, something that is considered as the main component ofhuman justice by philosophers like lohn Rawls (1975).
What might be the evolutionary interpretation of that sense of fairness shared with other primates? Could this behaviour be considered a primitive trait fixed during primate phylogeny several million of years ago? To accept the homology, other primates, such as howling monkeys, baboons, vervet monkeys, gibbons, orangutans, gorillas and chimpanzees, should have the same-shared character of fairness (see Fig. 2). However, as de Waal reported in his book Good Natured (1996, p. 94), only capuchins, humans and chimpanzees seem to show this sense of fairness.
Early latencies Laie latencies
Fig. 1. Prefrontal dorsolateral cortex (PDC) activation in early latencies (100-400 ms) and late latencies (400-1000 ms) when participants see both natural and artistic pictures qualified as "beautiful" or "not-beautiful" by participants themselves. The results show an activation of PDC under the "beautiful" condition in late latencies, with statistically significant differences.
This evidence is too weak to justify the title of my contribution to this conference. As final conclusions, I think that we can agree on the existence of an evolutionary ground of human values. Neurobiology can also provide useful items of evidence about how human values work. However, we are quite far from being able to understand the evolution of the set brain/values. Much scientific work is still needed, in my opinion, to accurately explain the evolution of aesthetics and ethics.
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