Carl Zimmer’s recent piece in the New York Times on evolvability is eye-opening. The study involved hundreds of generations of E. Coli evolving, with certain generations being frozen for later comparison:

The eventual winners still consistently beat out the eventual losers, the researchers found. On average, they ended up growing 2.1 percent faster than their rivals. Their success, in other words, was not the result of good fortune. They were better prepared to make the most of beneficial mutations.

The experiments have allowed the scientists to reconstruct the evolutionary race. The eventual losers initially pulled into the lead with mutations that gave them a short-term increase in their growth rate. But those mutations set them up for long-term defeat because when the additional beneficial mutations appeared, the losers enjoyed only a small increase in their growth rates.

The eventual winners, on the other hand, got a big benefit from later mutations, allowing them to pull ahead and take over the flask.

I recommend both the article and the original study. Fascinating.