Proton structure functions are currently described with excellent 
accuracy in terms of parton distribution functions, defined in terms of 
collinear factorization and DGLAP evolution. With decreasing x however, 
parton densities increase and are ultimately expected to saturate. In 
this regime DGLAP evolution is expected to break down and nonlinear 
evolution equations will take over. In the first part of the talk we 
present recent results on an implementation of physical DGLAP evolution. 
Unlike the conventional description in terms of parton distribution 
functions, the former describes directly the Q dependence of the 
measured structure functions and is therefore insensitive to 
factorization scheme and scale ambiguities. As a consequence it provides 
a more stringent test of DGLAP evolution and eases the manifestation of 
(nonlinear) small x effects. In the second part we present a recent 
analysis of the small x region of the combined HERA data on the 
structure function F2. We demonstrate that (linear) next-to-leading 
order BFKL evolution is able to describe the combined HERA data, once a 
resummation of collinear enhanced terms is included and the 
renormalization scale is fixed using the BLM optimal scale setting 
procedure.