Re: Mijn problemen met evolutie
Geplaatst: 17 aug 2009 12:15
Nog meer oranje ;
Adapting to your neighbors
Based on the observation of the newt in the coffee pot and because newts reveal their orange bellies when threatened, Butch hypothesized that poisonous newts evolved because they were favored by natural selection — since the poison helped defend them against predators. When it comes to natural selection, we tend to think of an organism becoming adapted to its physical surroundings (e.g., the climate, habitat, etc.) — and not necessarily to the organisms around it. For example, the white wintertime coat of the snowshoe hare is an adaptation that helps them blend in to the snowy landscape.
But in reality, both the biotic (living) and abiotic (non-living) environment can trigger evolution. For example, both turtles and snails have evolved hard shells that protect them from ravenous predators (part of the biotic environment). Butch wondered if newts had evolved their toxins in response to part of their biotic environment — in this case, to their predators.
Nasty newts!
To test his hypothesis that the newts were poisonous, Butch injected potential predators, like birds and reptiles, with different concentrations of a newt skin solution or offered them newts to eat. When exposed to the toxin, these predators became wobbly or weak in the knees. They sometimes vomited, stopped moving, or had a fall in blood pressure. All in all, the predators became very sick when exposed to newts. The evidence supported the hypothesis that newts had evolved a defensive poison. Shortly thereafter, chemists identified the newts' poison as a neurotoxin called tetrodotoxin, or "TTX."
Neurotoxins are incredibly dangerous. They act directly on nerve cells, which control everything you do. Some neurotoxins, like the tetanus toxin (which you can pick up by stepping on rusty nail carrying the tetanus bacteria) over-stimulate nerve cells, and cause all of the victim's muscles to contract at once. The muscles contract so intensely that they can break bones! Other neurotoxins, like TTX, cause nerves to stop functioning completely. A person poisoned by TTX stops breathing when his or her nerve cells stop sending the signal to breathe — but the victim's heart and brain keep working until they are depleted of oxygen several minutes later. Near death survivors of TTX-poisoning recall being paralyzed and unable to protest when others mistakenly declared them dead!
bronnen:
http://evolution.berkeley.edu/evolibrar ... warfare_03
http://evolution.berkeley.edu/evolibrar ... warfare_04
