Question

Hows does (Darwins "the origin of species") theory fit our modern understanding of genetics?

Answer 1

Darwin proposed that variations are present within the individuals of a  population. Some individuals possess traits which enable them to survive in a particular environment and reproduce to produce more number of offspring than other individuals of the species. This is called natural selection. As a result of natural selection, from the existing population, a new type shows prominence as more individuals of that type will be visible than individuals with other traits. As environmental conditions change( food, climate etc), some more traits which are already present in the population, become visible because of their advantageous role in survival of the organism. Accumulation of small variation aided by natural selection, results in origin of species.

Darwin could not explain the reason for the appearance of variation. With the discovery of the DNA, its function and structure, we now know that mutation in DNA brings about variation. Variations are random. When natural selection acts on variation and selects the suitable ones, variation gets a direction. For ex. in Galapagos island, Darwin observed Finches with different beak depths. It was due to their response to the changing environment. Beak shape became different because of occurence of different  mutations in different individual . During a draught, finches with deeper beaks were more likely to survive than finches with shallow beaks as it was difficult for finches with shallow beaks to crack harder and larger seeds. So. the former type adapted better and the trait from parent was transmitted to the offspring. This gave rise to a population of finches which are different from their ancestral type.