The sad fact is, all genetic material wears out with generations of propagation. Plants, animals, and people, the genetic material dies out, more quickly without genetic diversity. Not evolution, dissipation of gene integrity. Eventually, sterility and death of a species is possible.
With shattering of seeds and genetic diversity, plant species grow many variations and hardy ones persist or newer strains are produced. This book is a must read for anyone interested in FACTS about plant genetics; readable for a lay person with a 9th grade education yet deep and thought provoking. So glad this was conveniently available on Amazon.