Branches of Biological Study

Branches of Biological Study

Classifying and understanding the diversity of animal life is not the work of taxonomy alone — several specialised branches of biology supply the raw information that a classification is built on.

• Histology is the study of the microscopic structure of tissues — how cells are organised into functional layers and groups within an organ. It tells the taxonomist about internal organisation that is often invisible at the whole-organism level but can be diagnostic of a group.
• Embryology is the study of the development of an organism from a fertilised egg through cleavage, gastrulation and organogenesis up to birth or hatching. Because early developmental patterns (such as the fate of the blastopore) are extremely conservative across evolutionary time, embryology is one of the most powerful sources of evidence for animal relationships — it is the basis of the Protostomia/Deuterostomia split described later in this chapter.
• Ethology is the study of animal behaviour, especially instinctive and stereotyped behaviour patterns in a natural setting. Ethology and embryology answer very different questions: embryology asks how a body is built during development, while ethology asks how a fully formed animal behaves and interacts with its environment; both, however, contribute character sets that taxonomists use to group species. …