During the nomenclature section of last week's Systematics Workshop, there seemed to be one detail that, going by people's questions afterwards, seemed to cause the most confusion. This was the question of species name formation and gender agreement. I thought it would be helpful to give a (relatively) brief explanation of how this works.
The current system of species nomenclature is the binomial system, where every species is referred to by a genus and species name. Traditionally, these names have been derived from Latin or Greek, and even if not directly derived from Latin they are treated as if they were. Effectively, the binomen is a brief Latin phrase referring to a given species. Thus, Canis is a "dog", Canis familiaris (the domestic dog) is the "familiar dog". Lumbricus is an "earthworm", Lumbricus terrestris is the "terrestrial earthworm". Where this gets a little complicated for English speakers is that, unlike English, Latin (as well as Greek) is an inflecting language, where the form of words (usually the ending) changes to indicate their position and role in a sentence. The other major difference between Latin and English is that nouns in Latin (and Greek) have a fixed gender (masculine, feminine or neuter) that can affect their formation and sometimes the formation of words around them. It is important to realise that nouns may have a grammatical gender even if the object the word refers to does not have an actual gender. For instance "tabula" (table) is grammatically feminine, even though a table is obviously not actually female.
The name of a genus is always treated as a singular noun in the nominative case (that is, the case that would be used for the subject of a sentence)*. The species name can be an adjective or a noun in apposition** (in Latin, an adjective comes after the noun it refers to, which is why the species name follows the genus name). A "noun in apposition" is a noun that is being used as an adjective. For instance, in the phrase "small foot", the word "foot" is a noun and has the same grammatical role as a genus name in a binomen, while the word "small" is an adjective. However, in the phrase "elephant foot", the word "elephant" is a noun in apposition - it is a noun in its own right that is here playing the role of an adjective. In English, the distinction is generally not too significant (except, of course, we can change word order to say "the foot is small" but not "the foot is elephant"), but in Latin it makes more difference. Adjectives in Latin do not have fixed genders of their own - instead, an adjective will generally vary in form according to gender, and the gender and case of the adjective must agree with that of the noun it refers to. For instance, "tardus" is the masculine form of the Latin word for "slow". Were we to refer to a "slow man" (the Latin word for "man", funnily enough, being masculine), we would refer to a "vir tardus". However, if we were referring to a "slow woman", then the phrase concerned would be a "femina tarda" - note the change in the form of the adjective. Nouns in apposition, in contrast, do have their own fixed gender and hence do not chance to match the gender of the noun they refer to. Dusty Springfield may have been impressed by the son of a vir evangelizator, but she could have also considered the son of a femina evangelizator***. Whether a species name is an adjective or a noun in apposition is also important if the species is transferred to a new genus whose name differs in gender from that of the original genus. If the species name is an adjective, it has to change to match the gender of the new genus. If it is a noun in apposition, it does not change.
*In proper Latin, the form of a word would change depending on whether it was subject, object or some other factor in a sentence. For biological names, the role of inflection has been limited to the name itself, and you needn't concern yourself with its role in the larger sentence. For instance, it is correct to say "I saw a Tyrannosaurus rex", not "I saw a Tyrannosaurum regem".
**It may also be a verb participle - that is, the form of a verb that functions as an adjective (for instance, the "sleeping" in the phrase "sleeping dog"). The rules for verb participles are effectively the same as those for adjectives.
***Though it has to be admitted that the clash of genders give the latter phrase an inherent awkwardness in Latin that wouldn't exist in its English equivalent. It is linguistic differences like this that often make verbal humour so bloody difficult to translate from one language to another, while a custard pie is universal.
If the species name is an adjective, it is always in the nominative case to match the genus name. However, if the species name is a noun in apposition, it may be in either the nominative or the genitive (the possessive) case. The most common use of the genitive is if the species is named after someone - for instance, Gorilla graueri (the eastern lowland gorilla) is "Grauer's gorilla". Other uses of the genitive include cases where a parasite may be named after the host it was found on - for instance, the fish parasite Myxobolus cyprini would have been found on a carp (Cyprinus). The form of the genitive, of course, is determined by the rules of Latin grammar (note that singular and plural genitive forms differ from each other - from hereon in, references to the genitive form only refer to the singular, but authors do sometimes have cause to use the plural), and derives solely from the source of the species name - it is not affected by the genus name. It has become common practice to give the name of a species named after a person a masculine or feminine ending depending on whether the person being honoured is male or female*. There is no conflict whatsoever in placing a feminine possessive species name in a masculine genus - no more so than a gender conflict would exist in the English phrase "Julia's husband".
*This was not always necessarily the case - surnames used to be treated as masculine regardless of whether the person whose surname it was was a man or a woman. Conflicts have arisen from the change in practice when some authors have "corrected" older names honouring women but given masculine forms. Needless to say, the question of whether 'tis better to correct the effects of perceived past gender discrimination or to maintain established usage and spelling is a touchy subject that I'm leaving well alone for now.
When you look up a noun in a Latin dictionary, such as "woman", you'll see something like "femina, -ae. f." This indicates that the word for woman has the nominative form "femina" and its possessive form is "feminae", while the "f." indicates that the word is feminine. Latin nouns are divided into five "declensions", with each declension having its own set of case endings. The genitive (possessive) ending is given in the dictionary to indicate which declension the word belongs to, because the nominative ending varies more between words in a declension than genitive does. The genitive form also indicates the stem of the word to which the case endings are appended or which is used to form compound words if the stem is not clear from the nominative (for instance, "king" would be listed as "rex, regis" - the stem of rex is reg-, which is why we have "regicide" rather than "rexicide"). First declension words usually end in "-a", are usually feminine, and have the genitive ending "-ae". Second declension words end in "-us" (generally masculine) or "-um" (neuter) and have the genitive ending "-i". Third declension has no standard nominative ending, but genitive forms end in "-is" (apart from a few words derived from Greek with genitives that end in "-os"). Fourth declension nouns may be any gender, with masculine and feminine words ending in "-us" and neuter words in "-u", while genitive ends in "-us". Fifth declension names are usually feminine and end in "-es" with genitive ending in "-ei". In the majority of cases, though, a name ending in "-us" will be masculine, one ending in "-a" will be feminine, and one ending in "-um" will be neuter. If the genus name comes from any language other than Latin or Greek, then similar guidelines are recommended - names ending in "-us" should be treated as masculine, those ending in "-a" should be made into feminine genera, while most other endings should be treated as neuter. There are some exceptions to the above - for instance, "agricola, -ae" (farmer) is a first declension word ending in "-a", but is actually masculine, while "crus" (lower leg) might look at first glance like a masculine second declension word, but is actually a neuter third declension word with genitive "cruris"*. (And while I'm discussing dictionaries, I'd like to send an enormous "thank you" to the compilers of Perseus Tools. This is an absolutely fantastic resource with online searchable Latin and Greek dictionaries and grammars. It sometimes runs at the speed of continental drift, and can be a little temperamental, but there have been a number of times lately that I couldn't have done without it.)
*This last example has actually been my personal bane - one of the genera I work on is called Spinicrus and I have to continually remind myself that it's a neuter name, not a masculine one. When I published a checklist of described species of Megalopsalidinae (Opiliones) a few years ago, I corrected two species names that had been originally published in the masculine form to their appropriate neuter forms - then inadvertently wrote down two other names that had so far been correctly spelt as neuters in inaccurate masculine forms. Needless to say, I didn't notice my mistake until the published journal arrived in my mailbox.
Latin adjectives fall into two classes, one of which follows third declension while the other follows first and second declensions. First/second declension adjectives end in "-us", "-a" or "-um" for masculine, feminine or neuter forms respectively. Third declension adjectives do not differ between masculine and feminine, but do have different neuter forms - for instance, the word for slender is "gracilis" if masculine or feminine, but "gracile" if neuter. Dictionary entries for adjectives will give the masculine form followed by the feminine (if different) then neuter endings, e.g. "magnus, -a, -um" ("large") or "gracilis, -e".
Needless to say, there are cases where it may be difficult to discern how to treat a given case. It may be difficult to distinguish whether a species name is meant to be an adjective or a noun in apposition - "small foot" and "elephant foot" may be fairly clear, but what should we make of "human foot"? Most modern species descriptions will explain the derivation of a new species name, but this has not always been the case in the past. I'm not sure how the botanical and bacterial codes handle such cases, but the zoological code requires that in such cases the species name be assumed to be a noun in apposition and not subject to gender change if the genus changes. Similarly, if it is not clear whether a genus name is supposed to be masculine, feminine or neuter, the gender should be assumed according to the guidelines for non-Latin names explained above. In some cases that have been persistently confusing in the past, the zoological code mandates blanket solutions - names ending in "-cola" are masculine regardless of derivation, while names ending in "-ops" are masculine even if they were originally treated as feminine.
The suggestion has been made in the past that in light of the growing distance between biological names and their supposed Latin origins, as well as the general abandonment of Latin learning and usage, grammatical gender issues should be dropped for biological nomenclature. A species name, it is argued, should not have to change simply because the genus name does. This is a complicated issue, but I would like to point out that (A) it is only to speakers of non-gendered languages such as English that the process seems complicated. Conversely, to native speakers of gendered languages such as French, the idea of simply ignoring proper word formation borders on the obscene, not to mention the cacophonous; (B) not requiring genus and species names to agree in gender could potentially be even more confusing than the current situation, as instead of having general guidelines authors would have to remember the correct formation for every single name; and (C) many hundreds of species names have changed in the past as they were transferred between genera - what are to become of them (especially if they haven't held their original gender since some time in the 1700s)?