Based on observations made during a sea voyage in
a sail ship called HMS Beagle round the world, Charles
Darwin concluded that existing living forms share
similarities to varying degrees not only among
themselves but also with life forms that existed millions
of years ago. There has been gradual evolution of life
forms. A population has been built on variations, in
characteristics. Those characteristics which enable some
to survive better in natural conditions (climate, food,
physical factors, etc.) would outbreed others that are
less-endowed to survive under such natural conditions.