An additional 17 were cited for work involving only humans. Twenty-five of the Nobel Prize winners based their work on a combination of different experimental subjects, including vertebrates, invertebrates, and cultures. Even higher plants have been used as sources of model systems. A survey of this series of awards is but one indication of the contributions made by a variety of organisms to biomedical research. Diversity is seen in the millions of species that have existed or now exist, each of which has characteristics sufficiently different to enable them to be distinguished from one another.
Unity is seen in common anatomical features and in the universality of the cell theory.
For example, the development of all vertebrate embryos follows a program of blastula formation and development of ectoderm, mesoderm, and endoderm-a program that is characteristic of most invertebrates as well. Unity is also seen in the universal scheme of intermediary metabolism, which can be displayed on a chart and involves the relatively small number of approximately 1,000 intermediates. Furthermore, discoveries in molecular biology have demonstrated the universality of the genetic code, which applies from the simplest virus all the way to humans. In the last decade, knowledge and use of models and the capability of computer systems have expanded. A New Perspective that NIH support those proposals aimed at the development of model systems for specific fields of research.