What Should Aliens Look Like?

This post is a review of The Zoologist's Guide to the Galaxy: What Animals on Earth Reveal About Aliens and Ourselves by Arik Kershenbaum.

The author's basic idea is to propose that some aspects of life are universal - applicable throughout the Universe - and these principles can be used to make educated guesses about the nature of life on places other than Earth.

Motivation

The subject of the book has become topical especially in the last few years, as a large number (thousands) of exoplanets - planets that orbit stars other than our Sun - have been discovered and have raised the prospect of the discovery of life in the universe out there. Discussion of what that kind of life could look like is useful as it would help in its discovery, in communicating with it, and in coexisting with it.

Assumptions

We have a lot of confidence that the laws of physics and chemistry are universal. The author sets out to state those principles of biology (life) that are likewise universal. He assumes that:

i) If there is life there has to be death (I disagree with all three reasons he gives for this later in the book; for example, he says otherwise we would run out of space - Hey the universe is infinite as far as we can see! There's plenty of space out there - please bring on the immortality!).

ii) Living beings will need to eat, reproduce, compete, and cooperate (and hence communicate).

iii) If life and death are present there must be mutation and natural selection (independent of any specific biochemistry, e.g. DNA).

Characteristics

With such assumptions, the book says that evolution anywhere will generate similar solutions for similar problems, though the mechanisms might be different, as on Earth. Some examples of interesting aspects treated in detail are

i) Motion: This is necessitated by the need to find food, or avoid becoming food. The modes of motion developed by aliens will depend on what their planet is made of (has to be liquid solid or gas) and which forces it is dominated by (gravity, liquid viscosity, magnetic fields, etc.).

Thus, if the aliens live at the interface of a solid and a fluid (as humans do), they will probably have legs (which efficiently solve the necessity of having some frictional contact but not so much as to be a total drag -:)). They will probably also have bilateral symmetry (which evolved as it is more efficient than its absence - easier to walk/run than hop on one leg).

ii) Sex: The Universe is a hostile place and in order to survive, life needs to become complex and diverse; also, cooperation or sociality emerges from the unequal sharing of traits (blood is thicker than water).

But asexual reproduction leads to very little diversity as characteristic (genes for us) are generally not exchanged; and this kind of cloning basically leads to equal trait sharing for everybody. Hence aliens, if they are advanced, must be having sex.

iii) Communication: This is required for cooperation. The prediction here is that the physics of the planet will select the modality. In our own case, since light is blocked more easily by obstacles than sound, our preferred mode of communication is aural. If the alien planet has an atmosphere that absorbs sound, but allows light, their preferred mode might be visual.

There is a very interesting discussion in the book in this context about the attribute most scientists agree humans possess in the greatest degree compared to other animals - language. The book asks what language is, how can it be identified algorithmically (see Zipf's Law), and consequently how to detect signals from alien civilizations.

iv) Intelligence: Possibly an even more contentious topic than communication. The book tries to characterize intelligence (as a prediction machine useful for survival, as the ability to learn, as a means of inducing flexible behavior and hence Darwinian fitness, etc.).

There is a discussion about AI (the book came out in 2020), alien intelligence, personhood and whether aliens could be considered human in any sense. My favorite part: Alex the speaking African Gray parrot of Prof. Irene Pepperberg.

Conclusion

I found the book quite stimulating and informative. As might be expected, consideration of such a topic leads to deep meditations about what makes us alive and human, even more than it leads to realistic conclusions about the nature of alien beings.

Because we know so little about the rest of the (especially far-away parts of) universe, and because we only have a single example of a living planet, it is only possible to speculate about aliens. Thus the book's real accomplishment, in my opinion is to sharpen the questions, rather than to provide answers.

The writing is generally clear and tight, though some repetition could have been avoided, in my opinion. One of the things I really liked is the explicit mention of booktitles in the footnotes, which helped me mark several of them down for further reading (there is also a bibliography/suggested reading at the end).

Afterword

One of my favorite quotes from Arthur C. Clarke: It's not a UFO until you see the Mars registration plate!