gene flow or genetic drift can cause changes in a population
Do you mean what organelle? Cuz I think it occurs in all of our cells. You need an Endoplasmic Reticulum, I beleive.
D. Darwin's theory of natural selection shows that organisms evolve based on which one's survive the best and thrive.
The terrestrial gastropods are the only mollusks that have adapted to all the habitats of the Earth. They dwell in areas of high altitude, mountainous regions, hot and cold places. Land snails live and perform their vital functions on the ground and not in the sea or bodies of fresh water.
