The Laryngeal Nerve and Giraffe Evolution

[pevaquark (Matthew Pevarnik)]

@Jon_Garvey

The more interesting question is surely why the fairly common genetic variation of a direct left laryngeal nerve has not been conserved in evolution. We know evolution can do it, but we also know it hasn’t kept doing it.

Is it common? Has it been common for the past three hundred million years or so? Let me know what sources you are looking at as all I could find was something like this:

Non-recurrent laryngeal nerve (NRLN) is a rare anomaly which is reported in 0.3%-0.8% of people on the right side, and in 0.004% (extremely rare) on the left side.

Apparently though, the bulldog of anti-evolution arguments on this topic has been Wolf-Ekkehard Lönnig who is quoted repeatedly in Evolution News and other similar sites. Part of his argument is actually similar to your argument where he advocates for a ‘law of recurrent evolution’ which I could find nowhere referenced except by himself and articles on EN - which basically puts an extreme limit on what can occur over long periods of time variation of traits. I’m not sure of his intent or motives of course, but to an outsider it appears that he made up a law of biology so that he can use the law he made up against any arguments regarding the evolution of the laryngeal nerve. He also has a book on The Evolution of the Long-necked Giraffe.

@Jon_Garvey

Common descent - that’s more probable, or at least is once you’ve explained why the ability of even humans to produce a direct laryngeal nerve variation relatively commonly isn’t selected and preferred by common descent.

I think this is best visualized from a ‘fitness landscape’ perspective. A non-recurrent nerve would represent a maximum peak if designed from scratch of optimal design and a recurrent nerve would not. However, evolution doesn’t produce anything from scratch but only rather tinkers with existing material. So what kind of starting point did evolution have with the laryngeal nerve? One similar to how it is in fish where it is looped around the aortic branch. With this starting point in an ancient common ancestor - you would not have such big jumps and rerouting of nerves as slight variations would still look very much the same. With this starting point, this circulatory system evolved together, with slight variations here and there. Today, to change one of the major parts would be catastrophic to the organism without changing all the other parts around it - and this would not be selected for, despite it being a global maximum in regards to efficiency of design.