The only mutations I've ever observed result in deformed or handicapped people, and these seem to occur with startling regularity. Is there an example of a positive mutation which occurs with the same frequency?
Well, first, it should be pointed out that the probability of a usefull mutation is smaller than that of a debillitating mutation: most resault in a condition infavourable to the environement, or so damaging that the cell simply dies (in multicellular organisms; it undergoes apoptosis, ones that do not due to excessive damage can become cancerous.) Thus, speciation will only occur if we consider hundreds of thousands of years (obviously, a timespan inobservable to any human.) for macro organisms. Less for single-celled organisms.
However, there are examples of positive mutations (though, infact, they are negative as far as we are concerned.)
The pesticide and pharmaceutical industries are quite aware of these.
Some insects of a particular species will be resistant to pesticide X, and hence, when X is applied, the ones carrying this gene will replicate without competition from the ones who do not. Hence, a usefull mutation propogated by natural selection.
Viruses contain little to no error-checking, and hence, have considerable mutation. Because of this, it is extremely hard to treat them. The HIV virus is a specific example; infact, after infecting a new host, the strain soon mutates into a distinct phenotype from its predecessor. When applying pharmaceuticals to a patient, one cannot apply too much at once, or it will merely whipe out the competitors of the resistant strains, and render the drug useless for future applications.
A third example is penicillen and bacteria. Certain bacteria have develloped enzymes capable of disabling certain penecillins. Thus, penicillin can be modified to overcome this, but, eventualy bacteria devellop a resistance to that one as well; and kind of mutation is the major behind adding penicillins to foods; one wouldnt want to breed resistant bacteria!
-Andrew