Biology is defined as the science of living organisms. The diversity of activities contained within the field of biology is immense, and includes research into the origins, functions, and interrelationships of organisms, as well as the technological application of biological knowledge.

The idea that living forms gradually emerged through a process of evolution from much simpler forms in a branch-like system is no longer a contested issue in biology. Research into the fossil record, or palaeontology, and other subdisciplines of biology, such as comparative anatomy, biogeography, embryology, and genetics, have helped to trace patterns of common descent, including those between humans and primates. Charles Darwin's (1809–1882) theory of natural selection forms the basis of evolutionary theory, though other processes such as genetic drift and molecular drive have been proposed in addition. The relative pace of natural selection continues to be the subject of ongoing debate. The dynamics of genetic change in a population include mutation rates, migration of individuals from one population to another, genetic drift, and natural selection. The anatomical and behavioral differences within and among known hominid species can be traced. Other extinct species of humans have been discovered, though the consensus seems to be that Homo sapiens has a single original ancestor, who probably lived in Africa.

Ecology has enabled scientists to study more closely the way living organisms relate to each other. While early ecologists believed that ecosystems were stable and in equilibrium, this thesis has gradually given way to a more dynamic view, where contingency is predominant. Ecology includes not just the relationship between local communities of living things, but also extends to wider global and planetary systems. Some ecologists emphasize the idea of self-regulation within living systems, or autopoiesis, as well as the idea of emergence, understood in terms of properties that cannot simply be explained by upward causation from molecular mechanisms. Biosemiotics applies concepts from semiotics to elaborate the specific emergence of meaning, intentionality, and a psychic world. The latter can be compared to sociobiology, which tries to explain particular aspects of animal and human behavior by envisaging a shared biological and genetic origin.

The use of biological research to address specific human needs through biotechnology was given a radical boost following the discovery of the structure of deoxyribonucleic acid (DNA) in the 1950s. The ability to move genes from one species to the next has opened up the possibility of even more radical human intervention in the evolutionary process. The most controversial changes are those that manipulate the human species. Nonetheless, changes in the nonhuman world also raise questions that are of concern to environmentalists. The general increase in technological and industrial activity has put considerable strain on the planet, which many biologists consider to be near its carrying capacity in terms of its ability to support the human population. Loss of species through, for example, habitat destruction, climate change, or direct exploitation has promoted a growing concern for an environmental ethic among secular and religious communities. Such questions move biology outside the realm of pure science into the realms of the politics and the economics of poverty, posterity, and social justice.

See also BIOSEMIOTICS; EVOLUTION; LIFE, ORIGINS OF; LIFE, RELIGIOUS AND SPIRITUAL ASPECTS; LIFE SCIENCES; SOCIOBIOLOGY

CELIA DEANE-DRUMMOND