There have been many step changes over the 61 years since Watson and Crick’s DNA structure of 1953. For me the most dramatic was the discovery of the hox genes – the genes that parcel up the body into regions, creating limbs, for instance. At last some of the mystery of how biological form is created was dispelled.
A new science, Evolutionary Developmental Biology came into being in the 1980s. But despite many insights into the process of gene regulation and body building – especially in the fruitfly, whose body-sculpting genes are known in some detail – the mystery remained of how truly novel forms come into being. A new model car or aeroplane can be built from scratch – de novo. But all living things have to stay viable whilst genetic novelties emerge that eventually result in modified organs or an entirely new way of life. It is this that has provoked endless sterile debate since Darwin, with sceptics muttering about the likelihood of assembling a 747 in a gale.
Andreas Wagner points out the difficulty of understanding the complexity of gene interactions on the basis of isolated examples: “No list of examples, however long, could tell us how innovation through regulation is even possible”. Instead he shows how the complex circuits that link gene regulation are extremely robust: so robust that countless mutated genes can produce the same end result. Genes code for proteins and there are some examples of proteins that have the same 3D structure and the same function but in which every single amino acid has been replaced by a totally different one. As Wagner points out: this brings a whiff of Platonism back into biology after a very long absence. There do seem to Platonic forms of genes and proteins which the living tissue approximates to in its endless genetic dance of mutation, duplication and rearrangement.
Wagner has provided the answer to what the book jacket calls ”Evolution’s Greatest Puzzle”. There are countless linked pathways through this genetic maze, which means that a bodily organ or a physiological function can change gradually over time without ever losing its fitness. The process is a little like those puzzles in which one word turns into another via many steps, all of which must also be viable words. Of course, some genetic changes are lethal – we have always known this – but what is new is the knowledge of this remarkable robustness of multicellular creatures to genetic tinkering. We know, empirically, without ever looking at the DNA that this must be so: life forms do go extinct, but, on the whole, they are remarkably tenacious. But they also contain the possibility of novelty, which again we have known as an observable fact but now we know how it is done.