Ontogeny is the development of an individual animal or human from embryo to adult.
Phylogeny is the evolution of a biological species. The old idea that prenatal ontogeny recapitulates phylogeny once had the status of a “Biogenetic Law”. This has long been defunct. In the present context, what matters is the relationship between primary language acquisition and the evolution of human language. Both of these processes involve certain basic steps such as the following:

1. semiosis arises
2. gestures are used
3. vocal signs are yet unarticulated
4. gestures are replaced by articulated vocal signs
5. vocabulary, grammar and phonology are built up.

However, this parallelism is not because Adam and Eve learnt to speak in the same way that a modern child does, or due to some other specifically biological mechanism. Instead, both developments are cases of growing complexity in the same domain. The steps of this development partially follow the same order for two reasons:

• The domain in question is human language, which in itself is highly systematic. Its gradual formation therefore follows some very general principles (Dahl 2004).
• In both cases, language originates in the human brain. This is equipped with certain more general capacities which precede language and provide the basis for its development.