Human: The World Within

-No environment's static over time. The climate will change, the composition of organisms that live in that environment will change. -As a species, we've endured massive changes in our surroundings... cataclysmic shifts. Our greatest challenge has always been adapting. And that means constantly defending against all of the threats we face in the organisms that live among us. The immune system, essential to our survival every second, is the most complex and least understood piece of our biology. And that's because it's always changing. As new enemies crop up, this system meets the challenge......and is transformed. -The immune system is basically our body's defense system against all things foreign. Not only is our immune system effective at killing. It's also really effective at communication, memory, tagging other cells when it needs the help. It's a huge specialized army. -And to the naked human eye, it's invisible. Unlike other systems, where we can point to a center, like the heart or the brain, the immune system is a unique in that it lives...everywhere. And it is always on the move.