How can natural selection and isolation lead to speciation?

What is speciation?When a new and distinct species evolves from an ancestor speciesReproductively isolated from the ancestor/other species2. How does natural selection work?a. Population of individuals, with different heritable characteristicsb. Only the individuals most suited to their environment survive/reproduce successfullyc. Change in population genetics over time
SYNTHESIS (model answer)Over evolutionary time, new species are formed when barriers to reproduction arise in a previously interbreeding population. Reproductive isolation occurs when individuals are no longer able to interbreed to produce viable offspring, usually a result of genetic incompatibility of the gametes. Genetic differences arise as a result of natural selection and genetic drift. Natural selection happens when populations experience different selection pressures, so individuals with different heritable characteristics survive and reproduce in each population. Over time, populations become genetically distinct and reproductively incompatible, via natural selection. In very small populations, alleles may be lost when individuals die from chance causes. This also results in a change in population genetics over time, and can reproductively isolate the population as a result of genetic drift, rather than natural selection. Normally, both processes contribute to the formation of a new species.