Biology has undergone enormously impressive changes since the developmental contributions of Watson and Crick introduced the era of molecular biology. James D. Watson and Francis Crick were the two co-discoverers of the structure of DNA in 1953.

The more expositive aspects of the field, long associated with the older notion of biology as natural history, have been complemented by investigative insights that afford an understanding of life in terms of the precise characteristics of macromolecules (DNA, RNA and protein).

To a marked extent, control of cell functions, hereditary mechanisms, development of organisms, interactions between organisms and environment (ecology) and even evolution has become better understood by applying the probes of molecular biology.

However, the scope of life and its evolving new diversity needs a perspective of time and an appreciation of meticulous descriptive detail to be truly appreciated. One of the many values of the science of biology is that it opens our eyes to the hidden connections that link human beings to all other living things.

Continuity of life depends on the inheritance of biological information in the form of DNA molecules. The information is coded in thousands of discrete genes which are different segments of a DNA molecule, and DNA molecules as part of chromosomes are embedded in the cells.

In sexual reproduction male and female sex cells fuse during fertilization and thereby carry the genetic information with a combination one half from each parent. The sorting and combination of genes is due to independent assortment of chromosomes and crossing over during meiosis, and random fertilization occurs. In humans, the possible combinations are over seventy trillion.