A fascinating book that takes a look at life itself. From life and death, the hallmarks of life, the history of looking at how living things work, the border between living and non-living things and considering what life might be, this book is filled with interesting information and profiles of the people who have looked at the idea of what life is.

The first section looks at the beginning and end of lives, with a look at organoids and whether they could be considered to be alive. It then moves to the controversies over when does a human life begin and the battles over whether abortion should be allowed. A look at death and mourning among animals is then given, followed by a part on organisms that appear to defy death. The question of when a human is considered dead is then presented, with no clear answer given.

The next section looks at the hallmarks of life. Snakes are used to show just how much an organism can change the workings of its body when suddenly presented with a meal after a long fast. Slime moulds then show how organisms can make decisions about where to move to find food even when it does not have the equivalent of a brain. Bats then show how living consists of maintaining an inner balance of mechanisms (for both active living and hibernation) and what happens when it gets disrupted (by an infectious fungus). Maple trees then show that despite propagating millions of seeds, only a few will survive to produce the next generation. Evolution is then shown via a series of experiments on the bacteria that thrives in the lungs of people with cystic fibrosis, with the aim of making them less harmful to the lungs.

The next question looks at how people have historically considered something to be living. With views ranging from a god who 'breathes life' into organisms to a mechanistic view of life, a series of observations on an odd organism, the Hydra, which can regenerate itself from parts, would start a lot of discussions on life itself. Investigations and dissections of bodies would lead to an understanding of the body as a living system with many parts. Arguments over whether there was a vital force in living things would arise, leading to speculations of giving life to dead bodies (like Mary Shelly's "Frankenstein"). Ideas like 'living mud' from the bottom of the oceans would rise and fall. Vitalism itself would slowly fade as biochemistry began to show that the chemicals used by living organisms are no different from those in ordinary chemistry. Finally, genetics would be revealed when the role and chemistry of DNA would be decoded.

The last section would now go to the 'borders' of what is considered life. Viruses would be one that lies at the border, for while viruses can make use of living organisms, it does not have all the hallmarks of what is considered life. Ideas about how and where life began, in hot pools, deep sea volcanic vents, and so on would be debated. Exploration of planets like Mars on the moons of Jupiter and Saturn would push at the frontiers of the conditions where life could exist. Synthetic chemical systems would also be experimented with to determine whether they could be considered living.