Variation is small and directional but mutation is random and directionless
What is the meaning of this line?
Variation is small and directional but mutation is random and directionless
What is the meaning of this line?
It simply means that mutations happen and do not, in and of themselves drive evolution.
Mutations do not necessarily need to be advantageous or deleterious, they just happen and exist within the population at some low background. However when you combine mutation with environment and Natural Selection, then certain characteristics are favored while others are not. If there is a change in the environment, then what was once advantageous could become neutral or disadvantageous, while mutants that were always in the background end up with a competitive advantage. Also note that mutations need to occur in the germ-line in order to have any effect on the population. Mutations in somatic tissue cannot be passed from one generation to the next.
Evolution by Natural Selection (Darwinism) in contrast moves forward in one direction. Once change is selected for and speciation takes place, there is no turning back. The new species can not revert back to the old one. It moves in one direction, based on the conditions in the environment and individuals in the population capable of adapting to change should it arise. If the mutation has given those individuals a reproductive advantage within that environment, then their progeny will inherit the trait while the progeny of other may be less fit and reproduce less or not at all, and Evolution moves forward.
It simply means that mutations happen and do not, in and of themselves drive evolution.
Mutations do not necessarily need to be advantageous or deleterious, they just happen and exist within the population at some low background. However when you combine mutation with environment and Natural Selection, then certain characteristics are favored while others are not. If there is a change in the environment, then what was once advantageous could become neutral or disadvantageous, while mutants that were always in the background end up with a competitive advantage. Also note that mutations need to occur in the germ-line in order to have any effect on the population. Mutations in somatic tissue cannot be passed from one generation to the next.
Evolution by Natural Selection (Darwinism) in contrast moves forward in one direction. Once change is selected for and speciation takes place, there is no turning back. The new species can not revert back to the old one. It moves in one direction, based on the conditions in the environment and individuals in the population capable of adapting to change should it arise. If the mutation has given those individuals a reproductive advantage within that environment, then their progeny will inherit the trait while the progeny of other may be less fit and reproduce less or not at all, and Evolution moves forward.
