That daunting question is the subject of Nick Lane's latest book, Life Ascending - The Ten Great Inventions of Evolution. A British biochemist and writer, Lane has already proven himself a talented and fearless populariser of science: his first two books (on oxygen and mitochondria) were named book of the year by The Sunday Times and The Economist, respectively.

'[We] marvel and wonder at how we came to be here,' he writes in Life Ascending. 'For the first time in the history of our planet, we know.'

With a clear warning that much of our knowledge is still provisional, Lane plunges into the 10 key stages of the development of life - from its first stirrings in the sea to its profusion and division into the multitude of forms that live, and have lived, here.

His top 10 begins with the origin of life in undersea geothermal vents, and moves on to the workings of DNA, then the way photosynthesis turned our dusty red world blue and green, and the development of the complex cell. The others are sex, movement, sight, hot blood, consciousness and, finally, death, which keeps the wheels turning.

Lane does not simply rehash the old arguments; rather, he looks at new research and says which discoveries he thinks are correct. Darwin's primordial soup theory for the origin of life has now been sidelined, he notes. 'The first life was a porous rock that generated complex molecules and energy, right up to the formation of proteins and DNA itself.'

How do we know all this?

Lane explains the 'clever tools' that have clarified many of evolution's mysteries in recent decades. These include comparative genomics, which allows us to compare full genomes; imaging techniques that show us the functioning of neutrons in the brain while we think; and computational biology, which focuses computer science, applied mathematics and statistics on biological problems

'With these new techniques, a new breed of evolutionist is emerging, able to capture the workings of evolution in real time,' he writes.

On the molecular level, 'we can now see what actually happened over evolution, and why'.

Lane has the skilful populariser's knack of scattering vivid images and one-liners. Oxygen is 'without doubt the most precious waste imaginable'. Our energy is 'a beam of sunlight set free from its captive state in food'.

Some passages may slow the science-challenged reader, like this one, to a crawl, such as the inner workings of DNA and the complex cell. But the 'aha' moments elsewhere well repay the effort.