The Darwin debate forever confuses the different types of evolutionary statements. Especially in public discourse, over and over again, the theme of evolution is sold and taken thence to imply its mechanism. You are left to agree that since you agree to evolution you agree to natural selection. And this creates endless mutual misunderstanding. It is remarkable how little this distinction is addressed in promoters of Darwinism. For it is convenient to win two arguments in one, the bad part never making it to public discussion. Creationists have long been wise to this, hence the endless babble over the fact and the theory. Lovtrup's version more or less finishes the question.  

The main tenet of Darwin's theory is that his natural selection accomplishes evolutionary changes through the accumulation of some of those very slight individual changes which occur in all populations of living beings. The selection of these variations, and hence the direction of evolution, is such that the organisms become better adapted to the environment in which they happen to live. Since the struggle for existence is bound to be toughest between adults, it follows that Darwin's theory is a micromutation theory which accounts for evolutionary innovation primarily through the modification of adult organisms. 

This theory was professed ex cathedra when I went to school, and for many years I accepted it without contemplation or dissent. Now and then I read literature dealing with evolution, but being an embryologist I did not think that evolution was of direct concern to me. I do not know when I first began to suspect that there is something questionable in the state of current evolutionary thought, but I know who aroused my suspicions--Karl Ernst Von Baer and Richard B. Goldschmidt, and it is because I am an embryologist that their teachings had this effect. These two zoologists quite clearly demonstrated the the origin of the major animal taxa must be sought in modifications of the epigenetic, and notably the morphogenetic processes through which the fertilised eggs transformed, first into an embryo or a larva, and subsequently to a slightly deformed miniature of the adult organism. (This last statement is not valid for animals that undergo extensive metamorphoses.) And the main inference from this insight is that many of the mutations which have been really important from an evolutionary point of view must have been one-stroke changes of features distinguishing disparate major taxa. In other words, the views of von Baer and Goldschmidt imply that macromutations have been of great significance in organic evolution.  Introduction, p. 2

Soren Lovtrup's book, out of print and not so easy to obtain, along with Robert Reid's, is recommended for its critique, and its focus on development. Behind Darwin's perspective is the displaced developmental view which is now resurfacing once again in the age of the regulatory genes. Lovtrup focuses on epigenetics and isolates four different theories of evolution. This is one approach, useful as a reminder that the most basic questions tend to be scrambled by general accounts. Note the confusion of #1 and #2 below. The question of Lovtrup's epigenetics is also a debate and beyond the scope of this web page, although in the age of homeobox genes, it is worth rereading  Lovtrup's not easily obtained book. These distinctions can be useful for discussing the confusions of evolutionary theory.

1. The theory of the reality of evolution: this asserts that life on Earth originated through a process of evolution, as evidenced in the fossil record.

2. The theory on the history of evolution: If the reality of evolution is accepted then it follows that all living beings must be genetically related, and it also follows that this kinship must reflect the order in which the organisms have originated, that is, the history of evolution. ( In Lovtrup's, view the relationships of taxa and species are confusing, as the record of the Cambrian suggests. The title of Darwin's book is a misnomer, it should have been called 'On the Origin of Taxa'.)

3.  The theories on the mechanisms of evolution
           a. the epigenetic theory: epigenetics concerns the mechanisms responsible for the ontogenetic creation plants and animals. The phenomena dealt with by the epigenetic theory of evolution thus all take place within the confines of living organisms.

           b. the ecological theory: processes taking place above the level of the organism, the issue of survival of organisms, once created.

Cf. This viewpoint seems to be resurfacing in a new generation of work. Two recent works in the Darwin literature that begin to reflect considerations of this epigenetic viewpoint, Sudden Origins, J. Schwarz, or such a technical work The Origin of Animal Body Plans, Wallace Arthur (Cambridge, 1997)