Here are some areas where experimental evidence is limited in evolution:

1. Macroevolution: The process of large-scale changes, such as the origin of new body plans or phyla, has not been directly observed or experimentally proven. However, fossil records and comparative anatomy provide remote evidence for macroevolution.
2. Speciation: The exact mechanisms and processes of speciation, particularly in complex organisms, are still being studied and debated.
3. Origin of life: The exact pathway of abiogenesis, or the emergence of the first living cells from non-living matter, remains unknown and is an active area of research.
4. Evolution of complex structures: The detailed evolutionary history of complex structures like eyes, wings, or brains is still being explored through comparative anatomy, developmental biology, and genetic studies.
5. Punctuated equilibrium: This theory, proposed by Niles Eldredge and Stephen Jay Gould, suggests that evolution occurs in rapid bursts followed by long periods of stability. While it has some supporting evidence, it is still a topic of debate and research.