450 MYA photosynthetic eukaryotes made oxygen that formed ozone layer and cleared the way for terrestrial organisms. Reasons poorly understood. Why are species so well adapted for survival and reproduction in their own particular environments. Some variations within and between species are genetically based. In most species, the parents produce more offspring than can possibly survive to reproductive age.
Offspring inherit the traits of their successful parents.
Reproductive isolating mechanisms RIM s prevent interbreeding and keep species apart even when they are living in the same place. Competition forces species to specialize in species-specific feeding niches, lifestyles, microhabitats, etc. The disagreement is over the rates of evolutionary change. Gradualism Speciation is usually a gradual process. Speciation occurs because geographically-isolated populations gradually adapt to their different local environments.