Evolving the Alien: The Science of Extraterrestrial Life (2002, published in the US, and UK second edition as "What Does a Martian Look Like?: The Science of Extraterrestrial Life") is a book about xenobiology

Astrobiology

Astrobiology is the study of the origin, evolution, distribution, and future of life in the universe. This interdisciplinary field encompasses the search for habitable environments in our Solar System and habitable planets outside our Solar System, the search for evidence of prebiotic chemistry,...

 by biologist

Biologist

A biologist is a scientist devoted to and producing results in biology through the study of life. Typically biologists study organisms and their relationship to their environment. Biologists involved in basic research attempt to discover underlying mechanisms that govern how organisms work...

 Jack Cohen

Jack Cohen (scientist)

Jack Cohen, FIBiol is a British reproductive biologist also known for his popular science books and involvement with science fiction.-Life:...

 and mathematician

Mathematician

A mathematician is a person whose primary area of study is the field of mathematics. Mathematicians are concerned with quantity, structure, space, and change....

 Ian Stewart

Ian Stewart (mathematician)

Ian Nicholas Stewart FRS is a professor of mathematics at the University of Warwick, England, and a widely known popular-science and science-fiction writer. He is the first recipient of the , awarded jointly by the LMS and the IMA for his work on promoting mathematics.-Biography:Stewart was born...

.

In this book Cohen and Stewart argue that any investigation of extraterrestrial life

Extraterrestrial life

Extraterrestrial life is defined as life that does not originate from Earth...

 is too restrictive and unimaginative if it starts with the assumption that any advanced form of life must have similar characteristics to life on Earth

Life on Earth

Life on Earth: A Natural History by David Attenborough is a television natural history series made by the BBC in association with Warner Bros. and Reiner Moritz Productions...

, and must have evolved on a planet similar to the Earth (as in the rare Earth hypothesis

Rare Earth hypothesis

In planetary astronomy and astrobiology, the Rare Earth hypothesis argues that the emergence of complex multicellular life on Earth required an improbable combination of astrophysical and geological events and circumstances...

). They suggest that it is possible to make a scientific and rational study of the possibility of life forms that are so different from life on Earth that we may not even recognise them as life in the first instance.