Advocates of contemporary evolutionary theory argue that we can virtually witness evolution in action.
In the National Academy of Sciences educational guidebook, the authors state, The creation of a new species from a pre-existing species generally requires thousands of years, so over a lifetime a single human usually can witness only a tiny part of the speciation process. Yet even that glimpse of evolution at work powerfully confirms our ideas about the history and mechanisms of evolution. For example, many closely related species have been identified that split from a common ancestor very recently in evolutionary terms. An example is provided by the North American lacewings Chrysoperla carnea and Chrysoperla downesi. The former lives in deciduous woodlands and is pale green in summer and brown in winter. The latter lives among evergreen conifers and is dark green all year round. The two species are genetically and morphologically very similar.
Other examples cited in favor of contemporary evolutionary theory include drug resistance in bacteria, HIV and Plasmodium falciparum (a parasite that causes malaria), insecticide resistance in mosquitoes, changes in the average size of finch beaks and changes in the coloration of moths.
Critics, however, point out that the issue is not whether mutation and natural selection can produce minor changes; its whether these mechanisms can create new tissues, organs, limbs or body plans.
Biologist Keith Stewart Thomson, of Oxford University, points out that no one has satisfactorily demonstrated a mechanism at the population genetic level by which innumerable very small changes could accumulate rapidly to produce large changes: a process for the origin of the magnificently improbable from the ineffably trivial (emphasis in original).
Thomsons remark calls to mind the Cambrian explosion, mentioned earlier. But another problem comes from genetics. A profound surprise for evolutionary biologists has been extent to which the genes controlling the layout of various body structures have remained virtually unchanged across vast stretches of timeand are shared by organisms with vastly different body plans. Hence, the gene controlling the development of limbs in fruit flies is very similar to those controlling limb development in mice, tube-feet in sea urchins and spines in spiny worms. Yet these structures do not come from limbs in a common ancestor."
If one assumes that the controlling genes come from a common ancestor, this would mean that such genes originated before the structures they control.