**4. Concluding remarks and future research**

We have examined the evolutionary dynamics of a group of novel primate-specific genes (orphan genes) that have arisen by gene duplication. These genes typically form new structures in which only part of the protein sequence is shared with the parental copy, presumably because of partial gene duplication, and the rest of the protein sequence is unique. The orphan proteins accumulate a much larger number of amino acid substitutions per site than the parental proteins, denoting rapid functional diversification. The parental gene copies appear to act as "donors" of sequence but do not experience any obvious sequence evolution alterations, thus they probably preserve their ancestral functions. Future research in this area, using computational as well as experimental studies, should help clarify how frequent is partial gene duplication with respect to complete gene duplication, the differences in gene copy survival in both cases, and how partial and complete gene duplication contribute to the generation of evolutionary novelties.
