Let Us Speak of Giraffes

I've come across interesting information about giraffes from a couple of different sources recently, so I think a post is in order.

First is a new paper in BMC Biology. (I was going to wait until the final, formatted article was published, but the BMC journals seem to be taking for-ever formatting their articles.) Whereas giraffes are currently considered a single species with several subspecies, the authors reveal that:

"By analyzing mitochondrial DNA sequences and nuclear microsatellite loci, we show that there are at least six genealogically distinct lineages of giraffe in Africa, with little evidence of interbreeding between them. Some of these lineages appear to be maintained in the absence of contemporary barriers to gene flow, possibly by differences in reproductive timing or pelage-based assortative mating, suggesting that populations usually recognized as subspecies may potentially represent different species. Further, five of the six putative lineages also contain genetically discrete populations, yielding at least 11 genetically distinct populations."

The populations have distinct genetics, but also distinct fur patterns (i.e. pelage). Looks like speciation in progress. (BMC Biology 2007, 5:57)

Meanwhile, I have been reading Evolution: What the Fossils Say and Why it Matters by Donald Prothero. The closest living relative to giraffes is the okapi (left). However, the fossil record attests to other extinct relatives, although most are more like the okapi than giraffes. However, a yet to be published fossil apparently does show a neck of intermediate length (p. 317-18).

And speaking of the neck, in discussing the oddities of anatomy that occur through evolution, Prothero brings up the recurrent laryngeal nerve (p. 37-38).

Even more peculiar is the course of the recurrent laryngeal nerve, which connects the brain to the larynx and allows us to speak. In mammals, this nerve avoids the direct route between brain and throat and instead descends into the chest, loops around the aorta near the heart, then returns to the larynx. That makes it seven times longer than it needs to be! For an animal like the giraffe, it traverses the entire neck twice, so it is fifteen feet long (fourteen feet of which are unnecessary!).

He goes on to explain that this odd route is a result of historical constraints in evolutionary development based on fish anatomy.

I am also reminded of the last time I saw a giraffe at the zoo. I watched it chew its food, swallow, then regurgitate and continue chewing. The cool part was following the wave of peristalsis up and down the neck.

So there are a few things to think about (aside from tigers) the next time you go to the zoo.

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