As I’ve mentioned before, our focal animal, Sousa sahulensis or the Australian humpback dolphin, has only recently entered the official rolls of described species. In a recent report, scientists named this newly-identified species and thus spake Science- a species was born. Does that sound sort of arbitrary to you? Good, it probably ought to.
Let’s talk about species definitions for a second:
I love species names. I love using those distinct descriptions to identify the organism I’m looking at, and I love the way the fake-Latin words (so science! Very officialness) feel in my mouth. There’s a pleasing elegance to the system through which you can categorize groups of related species, like nested folders or bags-within-bags (kingdom, phylum, class, order, family, genus, species, subspecies). But do I trust species boundaries as absolutes? No, I do not.
A “species” can be defined quite a few different ways, is part of the problem. For example, the biological definition states that for a species to be valid, the population that makes it up must not be able (for reasons of geography, genetic change, or physical incompatibility, among other potential reasons) to produce viable, or fertile, offspring with the group from which it is being separated. Several issues arise with this definition.
First, we consider many animals to be part of one species despite the fact that they’re almost certainly never going to meet and exchange genetic material without the aid of humans. For example, northern and southern hemisphere killer whales in all oceans are still listed officially as Orcinus orca, which is absurd. They can reproduce in captivity, probably, but even groups of killer whales (for example, Southern Residents and the area’s Transients) that live in the exact same bays and straits avoid each other completely in the wild, and probably haven’t exchanged genes for tens of thousands of years. I could go on and on about killer whales and species definitions but I will spare you (for now, mwa-ha-ha) and move on to the next problem.
Second, some domestic animals like farmed turkeys, certain cows, and many dogs cannot reproduce without human assistance. Are they species? They can’t reproduce at all, in reality, so they don’t pass the “fertile offspring” test unless people intervene quite a bit (artificial insemination, cesarean section, etc.).
Some people don’t hold with the biological definition. They prefer to define a species based on the percentage of functional genes that are different between two groups (which varies wildly depending on the age and genetic purity of a presumed species), or physical characteristics that show distance between populations. There isn’t really a definition that captures the flawed system we have (understandably) superimposed on the natural world, and the flawed system doesn’t even capture the nuance that the evolutionary process constantly creates and changes.
Meanwhile, what do you do with mushrooms and plants that can self-fertilize, or other less-identifiable organisms like bacteria, constantly passing genes from one individual to another. How about viruses, just tiny packets of DNA and self-replication machines? People think of things in groups that feel natural (haha, biology = natural…) but that’s not very scientific. It is, however, very convenient and intuitive. We group things to make them study-able, understandable, explainable, referable. For the most part, the species definition really does work to distinguish different types of organisms. We just can’t explain exactly why.
So anyways, it’s a bit tricky to explain why Sousa sahulensis has been officially designated a new group within that system. In this case, a combination of geographic separation, physical characteristics, and genetic difference added up to the split of the Australian humpback dolphins from Sousa chinensis, the Indo-Pacific humpback dolphin. Tomorrow’s post will explain exactly how our Sousa have earned their species stripes- this is likely enough of a biology-nerd’s rant for today.
Stay posted, dearest readers! I’m going to go track down some more cute photos of our resident charismatic megafauna and then turn in- today was long, but wonderful. I’ll dream of manta rays and humpback whales and leaping dolphins- I hope you do too.