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THE title of Ed Regis鈥檚 comes from 鈥� a book that inspired physicists and other scientists to study biological systems, catalysing the field of molecular biology.

Regis鈥檚 book offers an update on the search for a suitable definition of life. On his wild tour of molecular biology and biotechnology, we encounter artificial cells, DNA and RNA, and the origin of life. Much of the material is familiar, but Regis is an entertaining and impressive storyteller: check out his anecdote about a 17th-century physician who studied metabolism by systematically weighing himself, his food and his excrement for more than 30 years.

Despite the book鈥檚 subtitle, readers looking for a treatise on synthetic biology will be disappointed. Regis spends a little time on it, but mainly sticks to topics that have been hyped in the media, such as DNA synthesis and synthetic genomes.

These are fascinating topics, but there鈥檚 so much more to synthetic biology. For example, engineers and biologists are now working together to design and build biological circuits out of proteins, genes and other bits of DNA. These circuits are being used to rewire and reprogram organisms, primarily bacteria.

The history behind this new circuitry and the characters involved in its development are colourful enough to make for their own book. In the early 1970s, for example, biologists realised they could use enzymes to cut a gene out of one organism and paste it into another. In this way, they could modify bacteria to produce proteins such as human growth hormone and insulin.

Many engineers, however, did not want to join this biotech revolution. They didn鈥檛 consider genetic engineering to be real engineering, but rather the biological equivalent of swapping a light bulb.

All this changed in the late 1990s, as the neared completion. With several organisms鈥� genomes sequenced and the 鈥減arts list鈥� of genetic components growing, scientists became increasingly interested in how genes and proteins interact in complex cellular networks. Since engineers are trained to deal with complex systems, some saw this as an opportunity to enter the genomics candy store.

鈥淓ngineers flocked to the genomics candy store鈥�

A few who entered realised that they could sidestep some of the complexity of cellular networks and instead use enzymes to create synthetic gene circuits in a cut-and-paste fashion. In this way, engineers could make biological versions of electronic circuits and rewire existing organisms just as they might tinker with a radio.

We can redesign life, but are we any closer to its definition? Regis thinks so. Synthetic biology and biotechnology have introduced the concept of 鈥渕inimal life鈥�. The common denominator of a minimally alive artificial cell and a minimally alive person (one in a persistent vegetative state), he argues, is metabolism. So while most definitions of life focus on the ability to replicate and reproduce, Regis argues that life is 鈥渆mbodied metabolism鈥�. It鈥檚 a provocative claim that is sure to generate debate.