BioMed
Every cell powers its chemistry the same way: it pumps charged particles across a very thin membrane, creating a voltage that it then taps for work. The voltage is only about 150 millivolts, but across so thin a layer that equals 30 million volts per metre, the strength of a lightning bolt. Because breathing, fermenting and photosynthesis all share this one method, it points to a single common ancestor for all life.
Complex cells began when one simple cell came to live inside another and both gained from it. The swallowed cell became a built-in power plant, and once cells made energy internally, the size limit was gone. Some of those first complex cells were about 10,000 times larger in volume. Cells rarely get inside one another and the pairing usually fails, which may explain why this happened only once.
Life appeared fairly soon after the Earth formed, then stayed at the simple level of bacteria for more than two billion years. The author argues the limit was energy: a simple cell makes its power only at its outer skin, so it cannot afford to grow much larger or carry many more genes. Complex cells arose only once in four billion years, with no surviving in-between forms.
Every complex living thing, from plants to fungi to animals, has the same unusual set of features, including sex, deliberate cell suicide and ageing. None appears in a comparable form in bacteria. The author argues these traits follow from the same energy constraints, so complex life elsewhere in the universe would likely evolve them too, including the need for two parents. This is a bold, testable claim, and reviewers note that its speculation often runs ahead of the evidence.
A steady voltage across a membrane would not form in open water or a calm pond. The author argues instead that life began at alkaline vents on the deep sea floor, where natural chemical differences already supplied stored energy. Early cells only had to wrap a membrane around that difference to use it. This is one theory among several competing accounts of how life began, and the book's evidence for it is partly speculative.