| Type | Biological systems |
| Purpose | Reproduction, evolution |
| Location | Throughout species |
| Variations | Diverse modes of reproduction • Wide range of sexual characteristics • Adaptations to various environments • Manipulation by biotechnological devices • Intentional genetic engineering |
| Historical and evolutionary development | Reflects the historical and evolutionary development of species |
| Involved hormones and neurotransmitters | Various hormones • Diverse neurotransmitters |
