Convergent evolution is the same biological trait in two species derived from different ancestry, within a biome. If that trait provides an advantage to the organism, it would be fit and could potentially reproduce and pass it down to offspring. It could also be called an analogous trait. For example, a bird has a wing and a butterfly has a wing however, bird wings contain bones and muscle and butterfly wings are more membranous. Although both can fly, their traits were not arrived at from common ancestry. Insecticide resistance is due to the fact that not all individuals in a species are exactly alike, according to the natural selection theory and due to pressure in the environment, for example, an insecticide, those with the best adaptations will live and pass on those adaptations. Perhaps when spraying insecticide, most insects will die, but a few will have a natural resistance in their genetic makeup. Those individuals will survive and pass this resistance gene to their offspring. Speciation and isolation has to do with the fact that if two species are separated geographically, for example, for a long period of time and then, if they should at some point, be reunited, if they can no longer produce viable offspring, they are considered two different species. While they were separated, different environmental adaptations would be selected for in each different environment the two populations inhabited. Therefore, after a long period of time, they may have so many differences, they can no longer interbreed. An example is the Galapagos Island finches. The theory is that an ancestral group of finches emigrated from Ecuador to the Galapagos and over a 2 million year separation, evolved into several new finch species. Heterozygote advantage illustrates why some genetic mutations persist in a population although they seem to be detrimental. An example of this is the gene for sickle cell anemia. The gene for sickle cell is codominant to normal red blood cells. There are three genotypes then, NN(normal) ss(sickle cell anemic) and NS(trait). The people in countries with malaria, who are heterozygous or have sickle cell trait (NS) actually have an advantage. They don't usually get the disease malaria. Thus, the heterozygotes have an advantage that people with normal red cells or sickle cells, don't have.