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6 replies
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The longest cell in the history of life
http://whyevolutionistrue.wordpress.com/2011/05/28/the-longest-cell-in-the-history-of-life/
One of my favorite “proofs” of evolution is the recurrent laryngeal nerve (RLN)—the nerve that innervates the larynx from the brain, helping us speak and swallow. It takes a very circuitous course, looping from the brainstem down around the aorta and then back up to the larynx. Here’s its course in humans:
It’s a prime example of “bad design”, that is, of the ham-handedness of any creator that was responsible for designing organisms. Of course, we aren’t designed, but evolved from very different ancestors. That’s why our bodies are full of glitches and kludges, and this nerve is one of them. It’s much longer than it need be, taking a tortuous route several feet longer than the direct path from brain to neck.
I’ve talked about the evolutionary reasons for this many times; you can see the full explanation in WEIT or read about it here. This diagram shows how it worked: the nerve used to line up with a blood vessel, both servicing the gills of our fishy ancestors. When the vessel moved backwards during evoution, the RLN was constrained to remain behind it, still retaining its connection to the larynx, which evolved from a gill arch. The nerve could not “break” to attain the shortest route, for that would not be possible by natural selection: it would interrupt the nerve transmission and be maladaptive. Click to enlarge:
?w=500&h=381
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Very interesting article http://whyevolutionistrue.wordpress.com/2011/05/28/the-longest-cell-in-the-history-of-life/
http://whyevolutionistrue.wordpress.com/2011/05/28/the-longest-cell-in-the-history-of-life/
One of my favorite “proofs” of evolution is the recurrent laryngeal nerve (RLN)—the nerve that innervates the larynx from the brain, helping us speak and swallow. It takes a very circuitous course, looping from the brainstem down around the aorta and then back up to the larynx. Here’s its course in humans:
It’s a prime example of “bad design”, that is, of the ham-handedness of any creator that was responsible for designing organisms. Of course, we aren’t designed, but evolved from very different ancestors. That’s why our bodies are full of glitches and kludges, and this nerve is one of them. It’s much longer than it need be, taking a tortuous route several feet longer than the direct path from brain to neck.
I’ve talked about the evolutionary reasons for this many times; you can see the full explanation in WEIT or read about it here. This diagram shows how it worked: the nerve used to line up with a blood vessel, both servicing the gills of our fishy ancestors. When the vessel moved backwards during evoution, the RLN was constrained to remain behind it, still retaining its connection to the larynx, which evolved from a gill arch. The nerve could not “break” to attain the shortest route, for that would not be possible by natural selection: it would interrupt the nerve transmission and be maladaptive. Click to enlarge:
?w=500&h=381
...................................clip
Very interesting article http://whyevolutionistrue.wordpress.com/2011/05/28/the-longest-cell-in-the-history-of-life/
The recent killing and dissection of the giraffe by on of England's zoos may/may not have also showed this property.
