ABSTRACT
A biome is a community of plants and animals sharing a mutual environment. The Earth has many overlapping biomes: savannah, high desert, arctic tundra, tropical rainforest, deep sea volcanic vents, and more. Each environment sustains its own unique mix of plants and animals. The skin on the fingertips responds to its subtly unique environment by forming whorls and ridges: fingerprints. Even identical twins have unique fingerprints; same DNA, slightly different environments. When discussing the brain, it is conventional to refer to the brain stem as the reptile brain, the midbrain as the mammal brain, and the cerebral cortex as the Homo sapiens brain, the brain that is self-aware. One way to understand how it is all organized is to consider how the body develops, from egg to embryo to infant to adult. But by turning on or off parts of its DNA, it can reproduce by cellular fission and give birth to any type of body cell.
