Nature. It presents a sophisticated investigation of how quickly the genetic codes for proteins are evolving - across the 3.5 billion years or so of life on Earth.
The idea is that the specific genetic codes, the sequences of amino acids, that describe proteins - the workhorses of molecular biology - cannot withstand big changes, otherwise the complex structures formed will just not do their job properly. Swap in a different amino acid somewhere in a chain of a thousand and you'll no longer fold this big molecule up into the right shape, and you've gone from a 1/2 inch wrench to a pair of tweezers.
Over time though small changes can, and do, occur. As long as the final outcome permits the same job to be done by the protein, all is well. Now, let's suppose that a whole clutch of modern organisms share a common ancestor (something we've touched on before in these pages). We should be able to see just how different the protein coding has become since that time, and we should be able to tell whether this type of gentle evolution has stopped or not.
Povolotskaya and Kondrashov apply to proteins exactly the same methodology that Edwin Hubble did to the measurement of the expansion of the universe. They look to see how fast the coding is changing as a function of how different those proteins are - just as Hubble looked at recession velocities versus the physical distance between galaxies. What they find is that after about 3.5 billion years the protein universe here on Earth is still, slowly, diverging and expanding - it's not yet reached a true optimal state. They also point out that while 98% of locations in a protein sequence can't deal with quick tampering (change an amino acid there and the whole thing ceases to work), over billions of years you could more or less re-write the code for a given protein and get the same function. That's a bit like changing Hamlet by one word every new print run, until you have a totally different script, but the same outcome.
So, what says all this for the nature of life in the universe? These proteins plays roles in things like metabolic processes that have remained unaltered for billions of years - solutions for how life extracts energy from its environment that are pretty close to optimal. Yet here we see a universe of slowly diverging, expanding, molecular structures - the very fabric of the biological cosmos on Earth. To my mind this might present a huge challenge to the notion of convergent evolution - the idea that there are a limited number of molecular or physiological solutions that life can use. Take a different planet, with a biosphere a couple billion years old. The stately evolution of its protein universe would almost certainly have taken a path unlike that here, exploring this vast multi-parameter space of molecular structures along alien paths. It both supports the notion of life as a potentially extraordinarily robust phenomenon, and as a hugely diverse one.