Evo-devo and the laryngeal nerve in giraffes; or, why intelligent design isn't. (Submitted to blog post)
So since I’m not inclined to submit 15 asks again, this time I’m giving you a cool bio lecture the *smart* way.
Developmental biology is, in my humble opinion, the coolest branch of biology. All beings that we know of start life as a single cell, which (in multicellular organisms) has the potential to become any one of cells composing any of the organs and tissues of that organism. It can and will become brain and heart and skin and stomach and even those most miraculous of cells, germline cells (the precursors to eggs and perm), which will maintain that miraculous capability to become any tissue, any organ, any part of the body. Developmental biology teaches us how that cell chooses what to become as it divides again and again, to form the billions or trillions of cells that will form the whole organism - which I will indulge in sharing some other day, the ways you can hardly tell fish from frog from human in the embryonic stage, because the underlying programming is so similar. But today, we’ll talk about how developmental biology support that Grand Unifying Theory of biology: evolution.
You see, the similar ways and patterns (and genes) that drive bodily development are some of our most powerful arguments for the singular origin of life, which then adapted and evolved into the myriad forms we see today. And some of these patterns show just how crazy any so-called intelligent designer would be. You see, development or new features in an embryo tends to work by adding on to old protocols and features; we can’t ‘delete’ an old program - stop the embryo from executing the pathway to make the start of gills, for example - without messing up the embryo and making it dead. This is why human embryos have gills (look for pics if you haven’t seen, it’s pretty cool!), even though humans aren’t aquatic organisms anymore. Now, gills on human embryos are odd enough, but we get some fantastically odd things in the giraffe.
In all four-limbed animals, there is a nerve that connects the brain and the voicebox (larynx) - this is called the laryngeal nerve. This nerve can be seen in fish, where it goes in a direct line from head to larynx, and is near their aorta (the large artery leading out from the heart). However, fish don’t really have necks; most land animals do. This meant that as the neck started to evolve, somehow the laryngeal nerve got ‘trapped’ below the aorta, and so made a sort of u-shaped path in the neck - it went down from the brain, under the aortic arch, and back up to the larynx. In most animals, this isn’t that much farther than a direct connection from larynx to brain, so it doesn’t seem to be a big deal. For human, it’s 6" to 12" longer than it 'should’ be if it were direct. But think, for a moment, of something with a long neck. Think of the giraffe.
The giraffe’s neck, we’ll say, is about 7 feet long. That means this nerve goes all seven feet down the neck, goes about an extra foot in the body looping below the aorta, and 7 more feet back up the neck. A giraffe’s laryngeal nerve is 15 feet long - when the distance from brain to larynx is about a foot! This nerve is 14 feet longer than it 'needs’ to be to connect brain and larynx - a compelling argument that either their was no intelligent designer, or that it had a lot of extra nerve lying around when it made the giraffe.
Bored, or ready for more?