Many acknowledge "Microevolution" but deny that Macroevolution occured.
The two pages below this one give extensive proof of Macroevlolution
Macroevolution is just microevolution over time
Many acknowledge that there is evidence of "micro evolution"; evolution that is witnessable today.
Examples might be the growing resistance of bacteria to medicines, the development of the thoroughbred race horse vis-a-vis the plough horse. However, those same people are unwilling to acknowledge that NEW SPECIES can evolve via evolution.
If we can change the characteristics of a species within our life time, doesn't it make sense that genetic mutations could have created a new species from an existing one over the last 300 million years?