The egg and the sperm is also living organisms and their previous interaction with the environment will also influence their joint product, the fertilized egg. Apart from DNA, the gametes from both parents also contribute the initial machinery of cellular material constituting the fertilized egg, and the DNA is just one component of this machinery. Through this transfer of biologically necessary material every human is directly linked in an unbroken physical chain with previous humans. The new genome resulting from fertilization is neither sufficient to construct a particular human being, nor has it a dominating role. It therefore seems that fertilization is just one single step in the process of creating a human individual.
Several steps occur before and several steps occur after.
Looking purely on the biology of a human fetus where the best description is an evolvement of features, it seems counterintuitive that its spiritual features should not also evolve in concert with its biological development. Roots of the genome Contemplating the nature and importance of the human genome, one realizes that this genetic code has evolved over a very long time. Most of the human DNA does not seem to be active at our present stage of evolution, and many genes and gene fragments are clearly a result of previous evolutionary steps in mammalian or even pre-mammalian history. One therefore gets the same impression of evolvement on the species-level as one gets on the individual level although the mechanics are different. Similar in both situations, however, is the complex interaction between environment and biology.