Sean B. Carroll the biologist explains in a brief New York Times article how animals have evolved different ways to cope with freezing temperatures. Unlike certain people I know who will "freeze to death" at five Celsius (that's 278 Kelvin), the real threat to animals is the water in the cells turning to ice. Interestingly, of all the animals that have evolved different anti-freeze methods, few have done it the same way.
On the contrary, Robin, some very unrelated species of animals have evolved resistance to tetrodotoxin, a powerful neurotoxin (2 mg can kill an adult human), in the same way, Carroll explains in an earlier NYT article. It is unusual that different animals protect themselves with the exact same poison, and the answer is that eating these animals is deadly not because they produce the toxins themselves, but ingest it when they eat certain bacteria that produce tetrodotoxin.
Carroll really is an excellent writer. I can highly recommend his Endless Forms Most Beautiful, and if you're serious about the molecular details, try From DNA To Diversity (you'll have to be very serious!).
In other news, researchers use a mathematical model simulating evolutionary pressures to infer that humans evolved dexterous hands not just because bipedalism freed hands for tool use, but because hands and feet use the same genes to build them during development, and changes in the development of feet thus affects how hands evolve, too. As others, I am skeptical that such an approach can tell us what actually happened.
14 hours ago in Variety of Life