In the absence of any examples of alien life, there is little we can definitively say about it, but Arik Kershenbaum in this book makes a respectable stab at deducing some constraints on the physical forms, consciousness, sociability and languages of alien species by working from the physics of the likely environments for life to occur, and on the processes of evolution.

Much of the argument is, to me at least, clear and sensible. There are areas that the author suggests are harder to constrain - biochemistry, genetics, reproduction. A particularly interesting passage discusses the genetics of bee reproduction and how that relates to the altruism of the worker bees.

Whilst I found much of the argument persuasive, the text can be somewhat repetitive and long-winded. It could have been condensed to half the size. The section on artificial intelligence came across as somewhat muddled. The author implying, without clearly stating, that evolutionary and competitive pressures would be equally applicable to artificial life - an interesting hypothesis in itself that would merit further exploration.

The last part of the book is a comprehensive bibliography of material that supports the authors arguments - a valuable resource in itself.

As an aspiring writer of hard sci-fi, I found it a thought-provoking read, worth the time spent on it. It underlined to me that, when devising alien species in fiction one should consider how the physical form relates to their environment and their ecosystem and the evolutionary process that led to that form.