Darwin's 4 Postulates
by CAROL CERVANTES VEIGUELA
There is a large amount of variety within a specie. One singe specie can have several branches that differ in minimal or major traits. However, they are part of the same specie!
Offsprings look like their parents due to their genetic ties. They are linked by common genes that form their phenotypes. Therefore, due to the mix of two individuals' phenotypes offsprings look like their parents–this is the inheritance of traits.
External stimuli might affect the survival of a certain specie. Factors like cold or hot weather, depredators, water bodies or the lack of them, etc. are some of the external stimuli that might affect the health of a specie; leading them, sometimes, to their extinction.
Traits that are no longer useful for a specie's life become extinct. They are no longer used and so they disappear with time. These traits do not affect the life of a specie once it dies out.