Arrival of the Fittest: Solving Evolution’s Greatest Puzzle, by Andreas Wagner

To explore the complex intricacies of life, from its origins to all its remarkable innovations, requires a unique approach to biology. In Andreas Wagner’s latest book, the evolutionary biologist describes how mathematics and computational biology have transformed our understanding of how these innovations evolve – given the basics in life’s molecular toolbox – and the conclusions are quite astounding.

Wagner starts at the very beginning, in a “warm little pond” that is in fact at the mouth of a belching, bubbling deep-sea vent – a nursery for chemistry to play and create in. Before life could be considered to be “living”, the first step involved chemical innovation – tiny fragments of ribonucleic acid, self-replicating molecules harvesting energy and combining chemical elements into life’s building blocks. From this early nudge, life gained momentum and has been unstoppable ever since.

It is true that life has had a long time to evolve and innovate, but can random mutations alone account for the overwhelming diversity that we find on Earth today? Wagner provides some mind-blowing numbers to help put into context the vastness of sequence space (the universal library of all proteins that have and could be created): in one small protein with only 100 amino acids, the number of permutations to explore is greater than 1 with 130 zeros trailing behind it.

If natural selection had to explore the entirety of sequence space each time a useful innovation arose, life would not have got very far. But what Wagner and his colleagues have found is that only a tiny fraction of the library needs to be explored before stumbling upon a specific innovation.

The ideas are big, and the numbers hyper-astronomical, but Wagner – whose previous foray into popular science writing was the award-winning Paradoxical Life: Meaning, Matter and the Power of Human Choice (2009) – has a gift for explaining the abstract. He tackles life from a new perspective, from its very origins to the hugely complex gene networks that drive life today. He goes on to show that these networks are not complex for the sake of it, but that they actually facilitate innovation, resulting in robust organisms that can tolerate and adapt to changeable environments. This can be readily observed when we consider organisms that have opted for a stable existence, like the symbionts that reside within host cells. The genomes and gene networks of such symbionts show markedly less complexity than free-living relatives.

Wagner offers a tangible and scientific explanation for such observations: “We have known for many decades that natural selection is not a creative force…[it] merely selects what is already there.” However, this familiar and uncontroversial sentence creates a paradox. “Selection did not – cannot – create all this variation”, and the space that selection must explore is too vast to meander through randomly. Chance cannot be the only factor. Only now, with our powerful modern experimental and computational toolbox, can we tackle this question. Biology and mathematics must first become intertwined before meaningful predictions can be made and tested.

What Wagner elegantly explains is how life innovates. He describes how the fittest can be found among all other variations; and far from being one needle in a haystack, the fittest is one of many needles in the haystack. Innovations propelled life from its simple beginnings to everything we see today – and only now are we are starting to understand where these innovations came from.