Pegg
Jehovah our God is One
First off, speciation has been directly observed on numerous occasions and is fully testable.
A clear example of what is believed to be speciation in action are 'Darwins Finches' It was believed by Darwin himself that the finches on the Galapagos islands had evolved into new species, hence why some had larger beaks and some smaller, and later researches also felt they were evidence of speciation.
These finches were found to be changing when the environment changed. After only one year of drought, finches that had slightly bigger beaks survived more than those with smaller beaks. And because biologists categorize them primarily by the size and shape of the beaks they believed that the changes proved speciation in action.
But now this is where it gets interesting. Peter Grant was the original researcher in the 70's who studied the finches...he went back in the late 80's and his findings were as he wrote in an article in the Nature journal in 1987 that they had seen a reversal in the direction of selection. What they thought were becoming new species of finch, actually weren't. And further to that they also found that some of the different 'species' were actually interbreeding with other 'species' and producing viable offspring.
What some have concluded from the study of the finches is that they were not producing new species at all...they were simply adapting to their environment.
Secondly, 40 years? Really? You do realise that 40 years is NOTHING when considering evolutionary time? We're talking hundreds upon hundreds of millions of years here...
Wolf-Ekkehard Lönnig of the Max Planck Institute for Plant Breeding Research in Germany has written about the intensive mutation breeding experiments that went on from the 30's thru to the 70's when researchers from around the world gave up trying.
And yet, you have not answered my question. What is the MECHANISM that in a genus stops it from changing beyond a certain point?
if we take the example of the mutation experiments, they repeatedly found that the number of new mutants steadily declined, while the same type of mutants regularly appeared. Lönnig deduced from this phenomenon the law of recurrent variation which is that genetically properly defined species have real boundaries that cannot be abolished or transgressed by accidental mutations and that the gene sequence will reach its limit so that no more variation occurs.