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Shark 6th Sense Related to Human Evolution?
An anonymous reader writes "Scientists at the University of Florida are claiming that certain genes found in sharks that give them their 'sixth sense' and allow them to detect electrical signals could also be responsible for the development of the head and facial features in humans. From the article: 'The researchers examined embryos of the lesser spotted catshark. Using molecular tests, they found two independent genetic markers of neural crest cells in the sharks' electroreceptors. Neural crest cells are embryonic cells that pinch off early in development to form a variety of structures. In humans, these cells contribute to the formation of facial bones and teeth, among other things.'"
As they evolved, mammals, reptiles, birds and most fish lost the ability. Today, only sharks and a few other marine species, such as sturgeons and lampreys, can sense electricity.
The platypus begs to differ...
Let's see, humans have: sight, sound, smell, taste, touch, pressure, deep pain, surface pain, referred pain, hot, cold, static equilibrium, and dynamic equilibrium. Some might even throw in thirst and hunger.
Pretty much, yeah. I think this whole "people have five senses" thing is silly. We really have nine: sight, sound, taste, touch, smell, heat, pain, balance, and body awareness (or proprioception, my favourite).
Proprioception is my favourite because of all the fun tricks you can play on it. If you close your eyes and I were to move your arm to some position, this is the sense that you use when you tell me what that position is. Also, there's the well-known trick where you stand in a doorway and press your arms against the side for a minute or so, then your arms feel "light" for a while. That works because you confuse this sense.
There's a similar one where you lie face-down on the ground, and someone lifts your arms off the ground and hold them there for a minute or so. When they release your arms, it feels like your arms go through the ground. It's a bizarre feeling.
http://en.wikipedia.org/wiki/Sense
09 F9 11 02 9D 74 E3 5B D8 41 56 C5 63 56 88 C0 Whoops, silly middle mouse button...
> I disagree that science is restricted to that which can be demonstrated using the scientific method. Humans have been engaging in scientific inquiries for millenia, yet the scientific method is a recent invention. The scientific method facilitates the acquisition of scientific knowledge, but it is not the only possibility. There are times when performing a scientific experiment is impossible or immoral. In these cases, we can still make observations and construct models, even though we cannot directly test those models.
It sounds like you're saying that "the scientific method" = "laboratory experimentation". If so, that's not correct. Astronomy, for example, uses the scientific method.
Also, "directly test" is a pretty slippery concept. Arguably nothing is direct, e.g. when we weigh a compound we are getting its weight indirectly (through whatever mechanism the scale uses), and we only see the output via the photons that our retina catches.
Sheesh, evil *and* a jerk. -- Jade
If I were asked to guess what embryonic tissue shark's electroreceptors came from, my first guess would be neural crest. After all, this is the tissue that gives rise to electrically active tissues like nerve and muscle, which have receptors that do indeed "sense" electrical fields. This is not to allow the animal to sense electrical fields in its environment, but simply the way nerve conduction and muscle contraction work--a change in electrical field (typically produced by a chemically activated ion gate in a membrane) is "sensed" by a voltage-gated ion channel that responds by opening up additional channels, further altering the electric field, which stimulates other voltage-gated ion channels, and so forth. It is easy to see how such a process could be evolutionarily adapted for sensory purposes, just as fish that generate strong electric fields, such as Torpedo (the electric ray) do so with tissues that are evolutionarily derived from muscle.
So basically, all this is saying is that we and sharks have a common ancestor and as a result share similarities in the development of nervous tissue (which we knew already), and that sharks' electro receptors develop from the tissue that any biologist would identify as the "usual suspect."