Recently the 150th anniversary was commemorated of Charles Darwin's letter which was read to the Linnean Society on July 1, 1858, on the subject of "natural selection", which was followed in 1859 by his famous book, On the Origin of Species by Means of Natural Selection, or The Preservation of Favoured Races in the Struggle for Life, often shortened to The Origin of Species. (Thank goodness!) In the process, he pissed off a lot of religious people, and they're still pissed off to this day. In fact, there's a whole industry of creationists who try to cast doubt on his ideas. One way they do this is by quoting any scientist who says that Darwin was wrong about any detail.
Of course, Darwin was wrong about many details. He was writing 150 years ago! Science has moved on since then, and discovered things like Mendelian heredity, mutations, DNA, population genetics, the genome, etc. Heredity was a particular problem for him, and he threw out a hypothesis which turned out to be completely wrong. However, he was right on most of the important stuff, like natural selection, common ancestry and descent with modification, all of which fit in nicely with later developments.
I have been interested in this subject since elementary school, and over the years I have occasionally been aware that there was some debate amongst legitimate biologists on the importance of darwinism, i.e. natural selection, versus other things, such as genetic drift. None of them claim that natural selection does not happen, just that other things are more important.
Recently, I read a blog post that clarified the debate for me. (I forget where, but will post a link when I find it.) I realize that what some are saying is that the title of Darwin's book was off! That is, that the origin of species do not arise through natural selection, but through processes such as genetic drift. This relates to the common definition of species as a population which breeds only with itself, and is incapable of breeding with other populations.
What happens when species originate is that a population becomes isolated for one reason or another from other populations, and over time these separated populations diverge genetically until they can no longer interbreed, even when they are no longer isolated from each other, because when they have sex with each other, fertilization does not occur, or the offspring may be nonviable or sterile in marginal cases, because their genomes are no longer compatible with each other.
Note that this has nothing directly to do with natural selection. Natural selection operates at the level of phenotype, allowing populations to adapt to their environments. However, natural selection alone is not responsible for preventing fertilization of unions. Natural selection can happen relatively quickly with large changes, and yet the different-looking groups can still interbreed. On the other hand, populations can differ little from each other outwardly and yet be incapable of interbreeding due to accumulated random mutations in their genomes, which takes a relatively long time to happen.
What we're talking about is two different aspects of evolution: phenotype and genotype. Phenotype is the outward expression of the genes, which is strongly influenced by adaptation through natural selection, while genotype is the sequence of DNA base pairs, which is affected by both selection and random effects including mutations and genetic drift. The phenotype is what we see changing during evolution, and the evolution of the genotype is invisible, but causes separate populations to become different species. Paleontologists study phenotypic evolution, because that's all that is preserved in the fossil record, but geneticists study genotypic evolution, which has only more recently been observable. For example, domestic dogs have evolved vastly different forms (although the selection was artificial, rather than natural), even though all breeds are almost identical genetically, and they can all interbreed with wild wolves; but there are species, such as various species of mosquitoes, which appear identical and yet cannot interbreed. (If you prefer vertebrate examples, I'm sure there are some, too.)
So even though Darwin is still right on the central laws of evolution: common ancestry, descent with modification by means of natural selection, etc., on the issue of how species originate, which is in the title of his book, he is now thought to have been wrong. However, to be fair, there are other, older definitions of species, for which having different adaptations was the important criteria, rather than genetic compatibility, so it could be considered to be more about semantics, and in the context of the science of his day, he was probably right. After all, he was talking about the "preservation of favoured races", by which he meant populations, and the means by which they came to appear in the record while others became extinct.
In any event, the creationists are never right, even if Darwin was wrong.