According to Gould and Eldredge, the reason why so many links are missing is that they simply do not exist. They take the view that biological evolution proceeds in successive stages of "punctuated equilibrium." Living species would remain unchanged for extremely long stretches of time, and then undergo profound changes in relatively short periods. To borrow a term from the quantum theory of atoms, evolution would occur in "quantum jumps." It is very likely that the spark of life appeared during the first such "jump."
Stephen Jay Gould