麻豆传媒

ONE thing I will admit to being quite pedantic about in my job as an editor is policing the use of the phrase 鈥渘ew species鈥�. It isn鈥檛 because I don鈥檛 like the concept 鈥� there are few things I find more exciting than a newly described organism we didn鈥檛 know about before. It is because there are so many ways to interpret 鈥� and misinterpret 鈥� the idea of a new species. But rather than this being a thorny issue worth avoiding, it is actually a fun mess of a problem that takes us to the core of many interesting issues in biology.

What is a species? The most familiar definition is that it is a group of individuals that can produce fertile offspring through reproduction. It feels correct to many 鈥� a blackbird can breed with another blackbird and produce young blackbirds that are able themselves to make more blackbirds. But this definition is no use for a wide range of species, such as plants or animals that clone themselves rather than reproducing sexually, or organisms that freely hybridise with many other species. And if breeding success is the way you assess if something is a species, it is impossible to apply the concept to fossils of extinct organisms.

There may be as many as 33 other definitions of what a species is, and you can see the sense in many of them. The morphological species concept, that a species is a group of organisms that look consistently distinct, just feels right on some level 鈥� but stumbles when species develop regional variations in colour or pattern yet still fundamentally seem to be the same organism.

A genetic definition suggests a species is a group of individuals that can reproduce and that have a distinct genetic profile. With the onset of DNA sequencing in recent decades, the genetic definition has opened the door to many more 鈥渘ew鈥� species being recognised.

It would be easy to jump to the conclusion that DNA analysis provides us with too many 鈥渘ew鈥� species to be useful, especially if they all look much the same as organisms we already knew about. But this isn鈥檛 always the case.

Often, undescribed species are hiding in plain sight. Take a giant isopod living in an aquarium in Japan. As we reported in our 20 August issue, it had been mistaken for another species, until genetic analysis revealed it was distinct. Upon closer inspection, researchers realised it had extra-long antennae and a yellower shell.

One reason it is hard to settle on a single definition for a species is because we now know the old methods for classifying organisms 鈥� into kingdoms, phyla, classes, orders, families, genera and species 鈥� don鈥檛 perfectly reflect reality. There is no reason why, for example, canids (the dog family) and rosaceae (the rose family) should each naturally subdivide in the same way. Are genera of the rose family as equally different from each other as genera in the dog family?

A more accurate, more modern approach is to think about clades 鈥� a clade is a group of organisms that are more related to each other than they are to anything outside the clade. Clades are nested within clades, on and on. Some contain huge numbers of organisms, some contain very few. Some evolved much earlier than others, and they can鈥檛 all be arranged symmetrically on levels of equivalence. It is a much better reflection of reality and helps us think about how life forms evolve, but for many practical purposes, it isn鈥檛 that useful.

When assessing the biodiversity of an area, for example, it can be useful to catalogue how many families or species there are 鈥� even if the distinction between each taxonomic level is a bit arbitrary. Unlike the impossible task of counting every clade, it is a practical process that provides useful information.

So, while 鈥渟pecies鈥� isn鈥檛 a perfect concept, it is an extremely useful one 鈥� helping us to catalogue roughly 1.6 million different life forms on our planet. And even at this time of heart-breakingly rapid extinctions, there are many more species yet to be discovered if we can get to them in time. One estimate suggests there are about 7 million unknown species out there, and another that there could be more than 9000 unknown species of trees alone. It is easy to find countless examples in recent publications, including multiple new species of , and .

Then why be so pedantic? Because, while I am comfortable with there being multiple definitions of a species, I am less comfortable with ambiguity in language. When we say 鈥渘ew species鈥�, do we mean it is a new product of evolution? Or a newly discovered species? And is it really new to all of humanity, or perhaps just to scientists or Westerners?

So language matters. But what could be more fascinating than learning of yet another species, however it is defined?

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