In the Tangled Bank, I wrote about how life has to evolve within constraints–constraints of physics, development, and history. One of the examples I used was the laryngeal nerve in giraffes. It travels down the giraffe’s neck, takes a U turn, and then heads back up again. It seems ridiculous, but makes sense if you think about how it was laid down in fish without necks, and was then gradually modified–rather than re-engineered outright–as tetrapods grew necks, and then taken to surreal extremes in the long-necked giraffe.
Youtube has an excellent snippet of Richard Dawkins hanging out with an anatomist as she dissects a giraffe’s neck, to show what this remarkable evolutionary legacy really looks like. Warning: it’s bloody, like all dissections. But it’s worth the gore!
(PS: Anybody know what show this came from?)
(PPS: Turns out, it’s from “Inside Nature’s Giants.” Wish I could see it from the States!)
August 30th, 2010 at 8:14 pm
Carl, the entire first season of Inside Nature’s Giants is freely availible on youtube with HD quality videos. That’s how I saw them. It’s a truly amazing show, well worth seeing.
August 30th, 2010 at 8:22 pm
Fascinating. This is episode 4 from season 1 of Channel 4′s “Inside Nature’s Giants.”
http://www.channel4.com/programmes/inside-natures-giants
August 30th, 2010 at 8:35 pm
What Dallas said. I stumbled on the giraffe episode a month or so ago and was hooked. From what I could gather the only episode produced but not available on YouTube was a lion/tiger comparison. I’m hoping they’ll work in a ostrich (or some other large bird) soon and maybe some large inverts (Humboldt Squid or giant octopus etc.).
August 30th, 2010 at 8:36 pm
[...] you, hive mind. (Actually, Dallas in particular.) Here’s the whole episode of Inside Nature’s Living Giants in which [...]
August 30th, 2010 at 8:38 pm
Thanks. Interesting vid.
August 30th, 2010 at 11:22 pm
Looks to me as if the recurrent laryngeal nerve of the giraffe could turn out to be a singularly poor choice with which to demonstrate how silly evolution is for not taking the direct path to the larynx from the brain.
From this Wikipedia diagram (http://en.wikipedia.org/wiki/File:GiraffaRecurrEn.svg), I would guess the nerve takes the path it does, looping around a kind of shunt between the abdominal aorta and the pulmonary artery, in order to prevent damage to either the abdominal aorta or the pulmonary artery, or both (but probably the abdominal aorta, considering that a branch of the recurrent nerve continues to descend) from a dangerous descending pressure wave in the carotid artery that would be generated if energizing the recurrent laryngeal nerve has the effect of blocking flow in the carotid artery.
It would do this, in my hypothesis, by opening up the pressure relieving shunt between the abdominal aorta and the pulmonary artery with the same nerve impulse that stimulates the larynx, but prior to that stimulation because the shunt comes sooner on the nerve pathway.
August 31st, 2010 at 7:47 am
It actually did air in the States several months back. My wife and I were watching it because we enjoy a good giraffe necropsy as much as anyone and about 15 minutes in the show was pretty much like, “oh, btw, and Richard Dawkins is also here.” In context it was pretty funny in a macabre sort of way.
August 31st, 2010 at 12:59 pm
[...] Giraffe’s Neck [...]
September 1st, 2010 at 8:01 am
It’s a funny episode this one because Dawkins states that the presence of the laryngeal nerve in girrafes is evidence of evolution and not a designer, because a designer would have gone ‘back to the drawing board’.
Quite apart from the dis-teleology (how does Dawkins know how the designer works if he doesn’t believe in one?), as you say Carl sometimes evolution works within constraints – just as designers do.
The oddest thing then, and perhaps most embarrasing for Dawkins, is that the rest of the dissection team go on to describe the ‘design’ of the giraffe’s heart and legs.
[CZ: Note the quotations marks you put around design. The other scientists use them too. As for evolutionary constraints vs design constraints, biologists can identify the constraints in which the giraffe neck evolved by comparing giraffes to their relatives--in other words, by reconstructing evolutionary history. What constraint would require a designer to make such an extreme detour? If you say we can never know how a designer works because it/he/she can do anything for any reason, then that designer is not the subject of scientific inquiry.]
September 5th, 2010 at 6:48 am
Sorry for plug….. http://scienceblogs.com/tetrapodzoology/2009/07/inside_natures_giants_iv.php
September 8th, 2010 at 11:49 am
“Quite apart from the dis-teleology (how does Dawkins know how the designer works if he doesn’t believe in one?), as you say Carl sometimes evolution works within constraints – just as designers do. ”
Well Ian the god folks have gone to great lengths over the centuries to tell everyone how omnipotent their invisible friend is ergo its easy to know how a designer with no limitations would work. And constraints dont apply to a GOD, it could just wave its godlike appendage and poof the giraffe is designed as desired. God’s dont need to worry about evolution hence God isnt designing lifeforms.
September 9th, 2010 at 2:39 am
Apart from the fact that 1. there is no shunt between the aorta and the pulmonary artery (the fetal connection closes prior to birth and is nothing but a bit of scar tissue in most adults), 2. there is no reason to believe that “energizing” the recurrent laryngeal nerve would in any way result in blocking the carotid artery, and 3. it is hard to imagine any sort of descending pressure wave from the carotid capable of damaging the aorta that won’t blow out the carotid itself first, even if this sequence of circumstances were real, it is very, very easy to imagine far more efficient ways of dealing with the problem than resorting to this ridiculous detour of the recurrent nerve, all which would be trivial for an intelligent designer to implement.
For example, you could:
1. Have the neurons whose axons within the recurrent laryngeal nerve are responsible for the blocking of the carotid fire later (accomplished by rewiring the neural control networks int he brain) and be separated out into a separate nerve.
2. Surround the carotid artery in a fibrous sheath that prevents it from being blocked.
3. Design the aorta to not be vulnerable to descending pressure waves in the pertinent pressure ranges.
These are just 3 of many many possibilities.
September 9th, 2010 at 2:39 am
Imagine the recurrent laryngeal nerve in a sauropod. . . .
March 6th, 2011 at 11:55 am
“A designer can go back to the the drawing board” — yes, but they very rarely *do*.
Particularly in complex systems — which even unicellular life is, let alone mammals — designers rarely to never go back all the way to the drawing board. A signal path’s exit from a bus is a long way from the bus’ origin and these days the destination is quite close? And this doesn’t happen in engineering? Please.
I’ve seen similar cabling runs in electrical wiring inside regular homes. And those are some of the most simple systems around.
Not that I think there’s an intelligent designer, mind you — this just isn’t a particularly valid argument, much as the existence of the eye is not a counterargument to evolution.
March 22nd, 2011 at 11:57 pm
“A designer can go back to the the drawing board” — yes, but they very rarely *do*.
I think the most important point is this. Dawkins is not comparing the “designer” to just your average “Ahh, I’ll let that flaw slide.. no biggie”-designer. We are talking about this omnipotent creator of the universe and everything sky-fairy.
Surely it is not that difficult to snap his fingers and fix that damned excess of wiring in that animal’s neck?