"It is the cause, it is the cause my soul..." - Shakespeare
Natural selection, the non-random selection of favourable traits in a limited environment, is responsible for the informational content of deoxyribonucleic acid; or DNA. The action of DNA was the cause that threw you (and indeed all life) into the world and determined your state of existence.
Therefore, to understand anything about who you are and where you came from it is crucial to understand DNA.
Discovering scientific knowledge
All scientific knowledge was once new knowledge:
Scientist's carry out experiments to isolate and identify causes. The data generated by their experiments either reveals the cause, the need to identify a deeper cause or uncovers an unexpected cause. This new knowledge forms a "brick", which other scientists examine and try to fit into the wall of knowledge already built. Sometimes the brick fits nicely, sometimes part of the wall has to be knocked down to accommodate the new brick while other times the bricks are discarded. In this way, the edifice of scientific knowledge is gradually built up.
In 1866 Gregor Mendel demonstrated that characteristics are passed from generation to generation in discreet units called genes. What these units were made of remained elusive; it was assumed proteins, the most abundant biological material, fulfilled this role.
In 1869 Fritz Miescher discovered an acidic substance in the nucleus of cells, which subsequently became known as DNA. In 1928, Griffith found that bacteria can share inherited material (genes) in a process called "transformation". In 1944 these findings were brought together when Avery, MacLeod and McCarty showed that DNA was the material that was responsible for transformation. This demonstrated that DNA forms units of inheritance.
How does DNA carry the information needed to build living things and how does it replicate itself so it is passed from generation to generation? Rosalind Franklin and Raymond Gosling generated an X-Ray diffraction pattern of DNA in 1952, which Watson and Crick used in 1953 to elucidate the structure of DNA. Remarkably, their proposal suggested answers to both questions.
See Nature 421 395-453