3.3  Organisms and their scientific names

Organisms are classified by scientists into hierarchies that reveal how they have evolved from common ancestors. We are not concerned with this evolutionary hierarchy in this course, but you should understand how the unique two-part Latin names that distinguish different organisms unambiguously to scientists have been derived.

The first part of the Latin name indicates the genus [jee-nus] of the organism (the genus is a subdivision of the much larger family to which the organism belongs). Organisms in the same genus are very closely related. The second part of the Latin name indicates the species [spee-sheez] of the organism, which tells you that it has certain unique characteristics that distinguish it from all other species in the same genus. The individual members of a species are not identical; for example, there are obvious differences between individual humans, but we all belong to the species Homo sapiens [homm-oh sapp-ee-yenz].

Scientific publications give an organism’s two-part Latin name in full the first time it is used, but generally abbreviate the genus to its first letter thereafter, as in H. sapiens. Note that the genus always begins with a capital letter, the species begins with a lower case letter, and both parts of the name are printed in italics (or you can underline them in handwritten notes).

Viruses and prions are not organisms, so they don’t have Latin scientific names. With these points in mind, we can describe the biology of each of the pathogen types that were listed in Table 1.