Natural selection acts by winnowing the individuals of each generation, sometimes clumsily, as old parts and genes are co-opted for new roles. As a result, all species inhabit bodies imperfect for the lives they live. Our own bodies are worse off than most simply because of the many differences between the wilderness in which we evolved and the modern world in which we live. We feel the consequences every day. Here are ten.
1. Our cells are weird chimeras
Perhaps a billion years ago, a single-celled organism arose that would ultimately give rise to all of the plants and animals on Earth, including us. This ancestor was the result of a merging: one cell swallowed, imperfectly, another cell. The predator provided the outsides, the nucleus and most of the rest of the chimera. The prey became the mitochondrion, the cellular organ that produces energy. Most of the time, this ancient symbiosis proceeds amicably. But every so often, our mitochondria and their surrounding cells fight. The result is diseases, such as mitochondrial myopathies (a range of muscle diseases) or Leigh’s disease (which affects the central nervous system).