Natural selection

• Evolution is the change in the inherited characteristics of a population over time through a process of natural selection.
• The earth is teeming with living organisms, including large animals such as mammals and fish, smaller animals like insects, and plants like ferns and trees.
• There are nearly 9 million different species of animals and plants on earth, and that number does not include microbes such as bacteria.
• Scientists believe that life first developed on earth more than 3 billion years ago, with the first life-forms being very simple, such as single cells.
• All species of living things have evolved from these simple life forms, a process scientists call evolution by natural selection.
• There is a massive amount of genetic variation within a population of a species, for example, with rabbits.
• Rabbits with alleles for thicker fur are more likely to survive colder temperatures, and these beneficial alleles may be passed on to their offspring over many generations, leading to a change in the population of rabbits.
• Rabbits with better eyesight or hearing are more likely to survive and reproduce, and these beneficial alleles may be passed on to their offspring over many generations, leading to a change in the population of rabbits.
• Sometimes two populations of one species can't become so different in phenotype that they can no longer interbreed to produce fertile offspring, and these two populations have now become two separate species, as seen with rabbits.