There has been a lot of debate about whether organisms evolve in a gradual way with changes occuring in a normal rate or often need sudden bursts of big changes followed by some small mutations. Now a days there is a compromise on both sides accepting each others argument. But I really have a problem with this model How big is really big in terms of evolution? I think we need to have a criteria to distinguish big changes from small changes. A mutation to one of the pigment proteins changes the colour of a flower attracting new pollinators and in another case a mutation in the Hox genes can create macroevolutionary changes changing crustaceans into insects. I think it is the interaction of the phenotype of an individual with its environment which will determine how big an evolutionary advantage or a change is to that species. What is a big change (changes produced by similar mutations) to one species may be a small change to another one.

I don't believe punctuated equilibrium is about big changes as much as it is about rapid changes. The "big," macroevolutionary change is what happens before an equilibrium gets punctuated, leading to a new evolutionary radiation. Once split off this new radiation radiates rather rapidly into all sorts of different niches and adaptive regimes. Then parts of the radiation get pruned off and the rest fall into a sort of stasis. Punctuated equilibrium is all about that alternating rhythm of lull and frenzy.

 

The classic example is the Cambrian 'Explosion,' but there are different interpretations as to how explosive that event actually was, now. You can still see a lot of demonstrations in primate evolution, though. Apes provide a good instance. They radiated out over three continents into all manner of niches available to large-medium sized primates, but then were pruned down into the piddling species today which have all have barely changed since the Pleistocene.