Ex uno multa

My friend Som and I love giraffes. Standing at the Southwick Zoo in Massachusetts, we watched as four adult giraffes and a calf meandered around their enclosure. We both were entranced by the odd beauty of these animals. Of course, then, the recent news that the giraffe we know is not one but actually four species was exciting, but came as a surprise to me, Som, and many others.

Four species of giraffe determined through genetic work (Image from NYTimes --see link above)

"It seems surprising that we didn't already know that," Som commented to me. Many others express the same incredulity that such a detail could be overlooked for so long. But here's a secret: many things you assume we know and understand we actually don't, especially if it connects to organismal relationships.

Take, for instance, a conversation I recently had with a professor in my department at Brown University. Her student (who also is a friend of mine) is interested in the breathing mechanics of snakes. Why? Because we have almost no clue how snakes breathe.

Shocking? Possibly. Unbelievable? Absolutely not.

To further digress on the subject, reptiles have an assortment of mechanisms to inflate their lungs--many lizards use muscles between their ribs called the intercostal muscles to pivot the rib back-and-forth. This expands the thoracic cavity, i.e. the rib cage, and increases the volume inside, enabling the lungs to fill up more space with air (see video below, on top). Thus air is drawn into the lungs until the intercostal muscles relax, closing the rib cage, and causing exhalation. Crocodilians have a special muscular system that attaches to their livers, acting much like a piston. This concomitantly operates with a few leg muscles to act exactly as lizard intercostals--contraction of the muscles expand the thoracic cavity, increasing volume and inhaling air (video below, on bottom). Snakes, on the other hand, pose an odd problem. Snakes "walk" on their ribs, but likely breathe by a similar mechanism as lizards (because snakes and lizards are related to one another--they're Squamates). How can you walk on your ribs and breathe simultaneously with them? We have a good idea that snakes actually don't breathe when they slither along, but they need to breathe at some point. So when sitting stagnant, how do they do it?

X-ray videos of an iguana and American alligator breathing. Videos taken using XROMM (X-Ray Reconstruction of Moving Morphology) at Brown University

This raises a point about biology--even the seemingly most straightforward topics present an enigmatic problem that we operate with under assumption for years, even centuries. Somewhat, that's the beauty of science, although eventually all assumptions must be justified.

In the case of giraffes, we assumed that all giraffes belong to a single species, broken down into multiple subspecies. In fact, the estimate of giraffe subspecies was originally 7-9, depending on the study. Now biologists have cut it down to five subspecies, all belonging to two of the new four species of giraffe.

But how do they know? Why break the assumption now?

To say that all assumptions are broken is slightly inaccurate, but this case relies heavily on collective evidence and firm statistical analysis. According to the original article, the authors suggest the presence of four species based upon "multi-locus nuclear gene analyses, morphological data, mtDNA sequences, and microsatellites." That spew of words translates to consistent and repeatable DNA information coming from both the nucleus and mitochondria--the powerhouse of the cell, which also happens to have its own DNA--as well as physical characteristics of giraffes. Add the statistical analysis and voila they know there are four species rather than one. (Well, it's actually not that simple, but close enough).

The thing is that much of the information was collected previously--these authors punctuated the former with unequivocal evidence in the form of nuclear DNA from the most inclusive sampling set and produced the clearest statistics yet. It's the combined efforts of multiple studies that gives power to this conclusion. Similar to a court case where substantial evidence validates a judgment, so it is in science. It was not only the work done by these authors that substantiates the claim of four giraffe species, but a combination of information together validates the claim.

But why was it overlooked for so long?

That in itself assumes that it was overlooked, which likely is not true. Surprisingly little is known about giraffes, as a short conversation with a giraffe keeper and quick study of giraffe literature will attest to. This might not be due to lack of interest, but more practical reasons such as lack of funding, ease of experimentation (always a challenge with large animals), value to our scientific knowledge, and exigency of knowing the facts. Unfortunately people cannot pick up their bags, fly to Africa, and collect information haphazardly about whatever he/she wants. Science costs money, and money comes from funding agencies that want to subsidize research that is justified and important.

In the case of giraffes, there is reason to be concerned and study them, but it was only appreciated in the past few decades. Giraffes, as with many organisms, suffer from habitat destruction, cornering the remaining populations into small segments of Africa (see image below).

Historical and contemporary geographical range of giraffes (Source: http://galleryhip.com/where-do-giraffes-live-map.html)

With newly ascertained knowledge that four species of giraffes exist, and that two of them are endangered, the value of this study suddenly escalates. Compounding this effect is the fact that biologists originally thought the giraffe population housed a highly diverse gene pool. Having four species, however, cuts genetic diversity in fractions. Low genetic diversity means greater chance of inbreeding, which often is detrimental to populations--case in point are cheetahs, which went through a "bottleneck" in genetic diversity not too long ago, leaving little diversity for evolution to operate with. This study, then, comes at a point when conservation management can still rescue decreasing giraffe populations.

So here's the takeaway: "simple things" in science are rarely simple and often unanswered; science operates through accordance of multiple studies to draw a conclusion; and some topics are left unstudied not for lack of interest, but lack of exigency or funding.

Overall, it's pretty amazing that we have four giraffe species living in Africa. That's exciting! A family of animals thought to only have two living species in it--the giraffe and okapi--has now more than doubled.

In the spirit of "scientific assumptions," though, I would feel remiss if I circumvented one topic that still has yet to be answered: What is a species? 

Let's leave that for a later discussion.



Want to help the conservation of giraffes? Interested in learning more about these superlative and majestic creatures? Check out the Giraffe Conservation Foundation to learn more about how you can help.