WARNING: Spoilers. Spoilers everywhere.

Christopher Nolan is back with a new film and this time he brings us millions of light-years away from our planet: in Interstellar, as in many other good sci-fi films, we travel to another galaxy and back to discover something about ourselves.

Many commentators and fans of the British-American director have discussed the science behind Interstellar. Articles have been published in Wired and other magazines and the discussion has flourished in the social media. Kip Thorne, theoretical physicist at Caltech and executive producer of the film, has written a book in which he explains the physics of relativity, space travel and wormholes (a.k.a. Einstein-Rosen bridges, for those of you who are into pompous names). Much less attention has been given to the biology in the film, probably because it contributes less to development of the plot. Nevertheless, in my opinion, it is essential to understand the message of the film.

Biology you say… you must mean the whole question about leaving Earth, a planet we have led to destruction, rather than try to save it. Well, no. That is certainly one of the themes and would need more extensive analysis. But I am an evolutionary biologist, and though I am very concerned about conservation and the fate of the Earth, my scientific interests lie elsewhere. What struck me as the main “biological” theme in Interstellar was altruism: a question raised multiple times in the film, mainly by Prof Brand and Dr Mann, and solved by Cooper, Dr Emilia Brand and the real protagonist, Murph. Prof Brand lies to Cooper about Plan A, the one to move all humans on Earth to the new planet, because he thinks that we are not able to sacrifice ourselves for the sake of strangers, even the whole humanity, but only for our families. We need to force ourselves to “think not as individuals but as a species”. But this is not part of our nature, it is something we almost have to impose on ourselves. Dr Mann, the Lazarus mission leader stranded on a planet of ice, goes even further than this and seems to suggest that the only thing that can save us, as a species, is our individual “survival instinct”.

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Cooper and his daughter Murph in the Film. Photo Credit: Paramount Pictures.

Though this is not clearly stated in the film, this view is based on kin selection theory, an area of evolutionary biology developed by British scientist W.D. Hamilton in the 1960s, which seeks to explain altruistic behaviour on the basis of Darwinian natural selection. Living things tend to maximise their fitness, which is their survival and reproduction, or better the number of genes they leave to the next generation. But this fitness has two components. One is direct and it is one’s own reproduction. The second is indirect and it is the reproduction of relatives corrected by one’s relatedness to them. If my sibling reproduces, I get half of that fitness, so to speak, because I share 50% of my genome with my sibling. This is the key insight of kin selection theory. From this, it follows that one should help (i.e. being altruistic to) another individual only if it is a relative and should not care about others (this is part of what is known as “Hamilton’s rule”). This is exactly the position defended by both Prof Brand and Dr Mann.

Cooper, Emilia and Murph, all three in their own ways, refuse this idea. According to them our nature is not selfishness. Hamilton’s rule explains animal behaviour fully, but ours only to a certain extent. We can love our neighbour and humanity as ourselves and our relatives. It is not something inhuman or abstract, it is our nature. Cooper sees no contradiction between love for one’s own family and for all humanity: “I am thinking about my family and millions of other families”, he says before landing on Miller’s planet. Murph does not give up on humanity and refuses to follow Plan B: she struggles to find the answer to “the problem of gravity”and ultimately reaches it, thanks to her father and, maybe, the mysterious “they”. Emilia is at the same time the most clear and most mysterious. Not everything about us humans can be explained by a simple biological rule. She is drawn to Edmunds’ planet not by reason alone, but by love, “the one thing that transcends time and space”.

Cooper, Emilia and Murph are all scientists, defenders of the power of reason as a light in a dark dystopian future, but refuse the idea that our current knowledge of biology can fully explain ourselves. This does not imply necessarily theism or belief in the supernatural: the film leaves this question open for each of us in the audience to seek our own answer and this is part of what makes Interstellar a great film. All three characters have their own answers I believe, but these are only hinted at vaguely. Emilia seems to suggest that, one day, science will come to understand humans fully, but at the moment it cannot; believers, on the other hand, may ascribe our distinctive characteristics to an all-loving Creator.

This is certainly not the point of the film. The point is that each of us has to decide whether we believe our ultimate nature is a selfishness of the kind described by Hamilton’s rule or, on the other hand, that we are capable of selfless love for our neighbour and that this is what makes us truly human. The message of the film is clear: the former fail in their effort to rescue our species from extinction and lose everything, while the latter, who are ready to sacrifice themselves, go through much trouble but, in the end, succeed in saving the whole human family.

NOTE: I apologise to anyone, in particular other biologists, who might think that my explanation of kin selection theory is simplistic. I have tried to present it in a way that is scientifically correct, accessible to non-specialists and does not turn this article into a BL3307 lecture. In this article, I do not present my position in any detail: this piece is meant to be a thought provoking commentary on the film.

Alberto Micheletti is a fourth year Evolutionary Biology student, with a particular interest in the evolution of altruism, great cinema and trying to combine the two.

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