Variation within species is one thing.
Evolution is another entirely.
Taking observed variation within species and extrapolating evolution out of it is presumptuous at best and not supported by actual evidence.
To make it easy, just focus on the human being. Show me any evidence anywhere that a change in the normal number of chromosomes in a human being has ever had either a positive or neutral effect instead of being deleterious.
No, variation within species is exactly the same thing as evolution.
Only the time period examined varies.
Over periods of thousands of years we see new sub-species.
Over, say, a hundred thousand years we see new species.
Over a million years we see new genera, etc., etc.
Always the processes are the same, only the period of accumulated changes changes.
metmom: "Taking observed variation within species and extrapolating evolution out of it is presumptuous at best and not supported by actual evidence."
What's presumptuous is ignoring clear evidence from fossils, morphological studies and DNA that variation within species over time becomes evolution of new species.
metmom: "Show me any evidence anywhere that a change in the normal number of chromosomes in a human being has ever had either a positive or neutral effect instead of being deleterious."
Nobody pretends that science has all the answers now, or ever will, but one clear advantage for us to the fusion of chromosomes in our ancient ancestors was it absolutely prevented any further cross-breeding between them and other great-apes.