In a paper just published in Nature, "Historical contingency and its biophysical basis in glucocorticoid receptor evolution," Michael Harms and Joseph Thornton describe creating an "ancestral" form of a steroid binding protein, and then testing thousands of evolutionary paths forward from the ancestral form to the present day protein. They found that two "extremely rare" mutations were absolutely required, that is, they had to be in place before the protein could ever evolve the ability to bind cortisol. Yet these two specific mutations had no beneficial effect on the protein by themselves, and so had to appear by chance!
Tracing these alternative evolutionary paths, the researchers discovered that the protein -- the cellular receptor for the stress hormone cortisol -- could not have evolved its modern-day function unless two extremely unlikely mutations happened to evolve first. These "permissive" mutations had no effect on the protein's function, but without them the protein could not tolerate the later mutations that caused it to evolve its sensitivity to cortisol. In screening thousands of alternative histories, the researchers found no alternative permissive mutations that could have allowed the protein's modern-day form to evolve. [Emphasis added.]
The above is taken from a news item from the University of Chicago Medical Center titled: "Evolution depends on rare chance events, 'molecular time travel' experiments show."
"This very important protein exists only because of a twist of fate," said study senior author Joe Thornton, PhD, professor of ecology & evolution and human genetics at the University of Chicago. "If our results are general -- and we think they probably are -- then many of our body's systems work as they do because of very unlikely chance events that happened in our deep evolutionary past," he added.
What Thornton's saying, I think, is that many mutations had to happen, with no help from natural selection, in order to make other mutations possible. And all these mutations somehow came together to make the proteins necessary to build functioning organisms. In other words, we were incredibly lucky.
Design is the better explanation, though. Think of it this way. When playing roulette, if you are looking for a specific number (mutation), you may have to wait a very long time to win your bet. You could then try again for another win, but you'd probably have to spin a long, long time to get the next winning bet. In fact, if you did keep on winning, spin after spin, everyone would wonder how you were cheating. Repeated bucking of the odds is always a sign of intelligent agency. Just ask the casinos.
Would it help to have millions of roulette tables, to continue the metaphor, all spinning at the same time to increase your chances at winning? Perhaps, but in biology, it's not enough to have the lucky neutral mutation(s) arrive. Things get lost more often than they last. Also, eventually all those scattered winnings from different tables have to be in one person's pocket. All the various permissive mutations have to come together in one organism.
That might sound trivial if everything was linear and tidy, like repeated spins of a roulette table, but evolution is anything but. Multiple incipient adaptive traits are being sampled all at once, each composed of various mutations, none of them beneficial yet. We have to abandon the roulette image here because it's too simple, too linear. Evolution is more like a vast sea of unrealized possibilities with someone dipping in a ladle and pulling out a sample to drop into the next sea. Getting a workable combination by chance is unlikely to say the least.
The odds are against it. I'm betting on design.