hes@ecsvax.UUCP (10/25/83)
It has been argued that evolution could not have occurred because we have never seen a new species evolve. While one could use the same argument against plate tectonic theory because we have never seen a new continent form..., instead I would prefer to offer an example. The radish and cabbage are in different species (also in different genera). One is able to cross them and the resulting hybrid plant is sterile (or pretty close to being so.) However, one can double the chromosome number (e.g., with one of the colchicine derivatives) and get a fertile plant, Raphanobrassica. This plant produces sterile progeny (or pretty close to being so) with its progenitor species. Raphanobrassica would certainly seem to be a new species. It appears that all of this could also occur in nature. Chromosome doubling does occur spontaneously, at a low rate. (In case you're wondering why anyone should try such a thing. Wouldn't a plant with a root like a radish and leaves like a cabbage be wonderful! Raphanobrassica does grow extremely well, but the moral is that it doesn't pay to mess around with Mother Nature. The plant has a root rather like a cabbage and leaves more like a radish! The thing has no commercial value.) --henry schaffer genetics dept. n.c. state univ.