Conversation between a biologist and a philosopher: identity, metamorphosis and the self (2)

Peacock butterfly (Inachis io) photographed at Thésée-la-Romaine, France. Daniel Jolivet / Flickr, CC BY

Two professors from the University of Lorraine discuss the tadpole and the frog, the caterpillar and the butterfly, two modern fables inspired by La Fontaine, and their implications regarding the nature of the self.

Proposition of Jean‑Pierre Jacquot

A tadpole having swum
all summer long
is amazed to find itself
transformed into a frog

A caterpillar soft and fuzzy,
when summer comes
witnesses the amazing sight
of being reborn as a butterfly

A baby all round and chubby
after many journeys
becomes a worn old man
at the twilight of his life

In the first article of the dialogue between a biologist and a philosopher, Roger Pouivet and I exchanged views on the nature of the self, in light of the material shifts induced by photosynthesis and respiration.

The thesis put forward by the biologist is that we are living organisms in constant exchange with the environment and hence our existence as an individual is a mere illusion.

The opinion of the philosopher was diametrically opposed, stating that a living being remains an unity whatever its physical composition. This initial exchange encouraged us to dig further into the nature of the self in light of recent (or very old) developments in biology. We also spoke with two German colleagues about our respective physical aspects as children, teenagers and later adults, based on photos at various stages of development. All of us being teenagers in the 1970s, it was enjoyable comparing the changes in style and appearance over time. While none of us is yet bald, it’s nevertheless noticeable that our hair has in general whitened and there’s a lot less of it compared to the days of “flower power”.

We were able to conclude that while it is not always easy to determine from a picture which teenager gave rise to which adult, in general one can do so with relatively high success. The situation got more complicated when my colleague Ralf presented me a photo of two children aged 5 to 6, one of them being himself and the other his cousin. Sadly, and to his despair, I failed to correctly identify him. (It happens that his cousin was less good-looking than he was at that age and so he was understandably a bit upset.)

I’m probably not particularly good at making such judgements and it is likely that a majority of adults would have picked the right child. However, if you present a panel with pictures of 10 babies and only one corresponding adult, it is likely that the rate of success would be closer to mere random selection. In other words, an observer who had no access to the history of the evolution of a human being could well fail to link the right baby to his or her adult form. In other terms, the individual has changed so enormously that the visual link is no longer there.

The alteration of the physical appearance of a living being is nowhere more remarkable than for those animal species performing metamorphosis, hence the introductory poems “à la La Fontaine”, a classic French author of the 17th Century who was inspired by Aesop’s fables. It is quite obvious that in the absence of genetic data, an observer would have no idea that a caterpillar transforms itself into a butterfly or a tadpole into a frog because of the remarkable differences between these organisms at different stages of development.

These observations generate a paradox, as it’s obviously impossible to say that a butterfly is identical to a caterpillar, yet we know that these two forms of life correspond to a single species. Given these examples, the question that can and should be asked is the following: Although we know that a human egg and sperm, when combined, will give rise to what will one day become an elderly man or woman, should we nevertheless consider that its self is unchanged through all these transitions?

I believe that we can clearly answer no to this question based on a number of observations. The first is that all along these transitions, the material composition of an individual has completely changed. It is highly likely that none of initial molecules and atoms that constituted the egg are retained in the later adult. Everything has been reshuffled via nutrition and respiration. In other terms, the physical and chemical nature of an individual has totally changed over time, and he or she is not physically the same. One’s intellect capacities also evolve in parallel – the cognitive and social capacities of a new-born are extremely different from those of an adult and can diminish again with senescence.

Altogether, these considerations lead to propose that an individual does not remain unique all along his life cycle. Instead, he or she is subjected to successive transformations that deeply change the identity and the nature of the self. Somehow the notion of the self needs to include all stages of transformation of an individual from genesis to final dissolution. However, it is quite clear that no observer has access to the entire developmental process. In our social interactions we are dealing more or less with a succession of snapshots of a given individual.

In the exchanges with my colleague philosopher Roger Pouivet, I understood that for him the state of conscience of a human being, or in other words his self or his soul, are linked to the material aspects of the body. It will be interesting to hear his comments to this analysis.

Response by Roger Pouivet

Does an individual who physically changes upon ageing nevertheless remain the same? The answer of Jean‑Pierre Jacquot to this question is essentially no. Instead, he suggests that the identity of a person, i.e. itself, is an illusion.

The dualists contend that the identity of a person is not physical, but mental or psychological. In principle, a spirit could be introduced into another body. In a famous text, “Essay on Human Understanding”(II,XXVII,&9), Locke states that a person is “a thinking intelligent being, that has reason and reflection, and can consider itself as itself, the same thinking thing, in different times and places”.

He adds :

“For should the soul of a prince, carrying with it the consciousness of the prince’s past life, enter and inform the body of a cobbler, as soon as deserted by his own soul, everyone sees he would be the same person with the prince, accountable only for the prince’s actions: but who would say it was the same man?”

And also

“The same immaterial substance or soul does not alone, wherever it be, and in whatsoever state, make the same man”.

Locke questions the metaphysical nature of a person. He distinguishes rigorously and clearly “individual”, “man”, “person” and “soul”. The problem that he addresses is not scientific in such a way that biology could answer it. It is a metaphysical question that requires metaphysical answers. To know what identity is, especially personal identity, one does not perform an empirical quest. It is a question of concept analysis, of thinking about their significance, of arguments.

In my preferred metaphysics, human beings are composed of a rational soul and matter. The rational soul constitutes their specific identity, i.e. makes them the human beings that they are. The rational soul is immaterial. However, each human being is individualized by its material appearance. The progressive modification of a body that remains specifically human does not imperil its personal identity.

This is the problem of the Ship of Theseus. The constitutive elements of the ship are replaced one after the other along the trip. Is it finally the same boat when it returns to the harbour? One can contend that the change of one plank is not sufficient to change its identity, and the same goes for me when after I have a haircut. After each step only part of the boat becomes different, there for it is the same boat that goes back to port even if all pieces are now different. Similarly, a woman does not necessarily find that her husband has changed after each haircut…

It follows that if the cell replacement of a living being is progressive (and there is every reason to believe it), the individual’s appearance may change enormously but he or she still remains the same. The metamorphosis of a tadpole into a frog is indeed a striking change. But is it decisive from an ontological point of view – in other words, concerning what a living being is – to the point that the original creature has been completely eliminated?

In a tradition inherited from Thomas Aquinas, to which I adhere, the metaphysical nature of a human being is hybrid: an immaterial soul makes us what we are and our body is specific to us. This doctrine is not the one of Locke, for whom personal identity is based on psychology and memory.

Several other metaphysical proposals deal with this question. That is the occasion to mention the book by Eric T. Olson: What Are We? A Study in Personal Ontology. His solution differs from those of Thomas Aquinas and Locke. Among others, this book should be enjoyable for biologists like Jean‑Pierre Jacquot who have an interest in metaphysics.

This article was originally published in French