The same is true for other species. Some famous male racehorses have sired hundreds of offspring, others, for whatever reasons, produced none. Some individual variations simply don't live long enough to reproduce. It is common to find walnut seedlings which are white because they lack the gene for production of chlorophyll. The next generation will be made up of the offspring of this generation.
Variations constantly arise through mutation of DNA in the germ cells.
The DNA has to be copied many times and random copy errors have a probability of occurrence. In the latter case they won't be seen until they become common enough in the population for two to come together at fertilization. An organism's chance of survival or reproduction will largely be controlled by the relative suitability of its characteristics to the conditions in its environment. The walnut without chlorophyll has no way of obtaining the energy it needs to survive. The control exerted by environmental conditions on reproductive success is called Natural Selection .