The equation F=ma does not postulate random mutations and natural selection as sole causes for the speciation observed today, either.
Neither does evolutionary biology. Heck, neither did Darwin.
To dispel the myth that Darwin ever considered that natural selection might be the "sole" method of evolution, one needs only read this passage from the 1872 edition of On the Origin of Species:
"As my conclusions have lately been much misrepresented, and it has been stated that I attribute the modification of species exclusively to natural selection, I may be permitted to remark that in the first edition of this work, and subsequently, I placed in a most conspicuous positionnamely at the close of the Introductionthe following words: "I am convinced that natural selection has been the main but not the exclusive means of modification." This has been of no avail. Great is the power of steady misrepresentation."
I really wish people would try to learn some biology before they attempted to critique it.
As I understand it Darwin was averse to the notion of presenting the origin of species as a progression from simple to complex. Today's high school biology books may cause him to roll over in his turtle soup. And no, I would not think him or his followers to be so simple as to posit mutations and natural selection as the sole determinants of biological history. The question is whether these two things can be understood and applied in any way other than post facto, ad hoc explanations for speciation.