A (a)   is a group of living organisms consisting of similar individuals capable of exchanging genes or interbreeding. The species is the principal natural taxonomic unit, ranking below a genus and denoted by a Latin binomial, e.g. Homo sapiens.

A (a)   is any change in an organism's environment that causes the organism to react.

Any behavior of a living organism that results from an external or internal stimulus is a (a)   .

(a)   is any self-regulating process by which biological systems tend to maintain stability while adjusting to conditions that are optimal for survival.

In evolutionary theory, (a)   is the biological mechanism by which organisms adjust to new environments or to changes in their current environment. ... The idea of natural selection is that traits that can be passed down allow organisms to adapt to the environment better than other organisms of the same species.

(a)   is a systematic and logical approach to discovering how things in the universe work.

A (a)   is a supposition or tentative explanation for (a group of) phenomena, (a set of) facts, or a scientific inquiry that may be tested, verified or answered by further investigation or methodological experiment.

A (a)   is a supposition or a system of ideas intended to explain something, especially one based on general principles independent of the thing to be explained.

A (a)   in science is a descriptive generalization about how some aspect of the natural world behaves under stated circumstances.

(a)   is the gathering of information through the five senses. Scientists use sight, smell, hearing, taste, or touch to learn about our world.

(a)   are explanations for observations you make and are based on your experiences and what you know.

(a)   is an evaluation of scientific, academic, or professional work by others working in the same field.

(a)   -moral principles that govern a person's behavior or the conducting of an activity.