This essay was recycled from my website (November 21, 2009).
Absurd creativity—that is what evolution has. The pathways of evolution follow no course of deductive logic, to design organisms or ecosystems the way an engineer would. Evolution tries all kinds of things, some beautiful, some silly, some ordinary—and keeps the ones that work. There is no Designer/Engineer in control of the process; it just spreads out in a million directions and produces adaptations that are essentially unpredictable.
This was brought to my attention as I was writing the entry about reptiles for my upcoming Encyclopedia of Biodiversity. Like most of you, I just assumed that any legless reptile that slithered through the undergrowth was a snake. But this is not correct. There are about a dozen different lineages of partially or wholly legless lizards, which have evolved the same adaptation as snakes, but independently. Lizards have long tails, whereas most of a snake’s length is its body. “Glass snakes” are actually lizards, without legs, and with a long tail. They are called glass snakes because they can break off parts of their tails (like broken glass) to confuse a predator that is pursuing them. Real snakes cannot do this. Legless lizards are examples of evolutionary convergence, where different lineages of animals independently evolve the same adaptation.
One day about a billion years ago (seems like yesterday), the first plant cells got their chloroplasts. These are the green structures that make sunlight into food. It might really have just happened in one day. Photosynthetic bacteria invaded, or were consumed by, larger cells with nuclei. But instead of killing or dying, these bacteria took up residence inside the plant cell. It was a mutually beneficial relationship; the bacteria made food from sunlight, and the larger cell provided fertilizer and protection. The chloroplasts of plants are cells inside of cells. From this event, the red algae and the green algae separately evolved. Some of the green algae evolved into land plants.
But there were some other large cells that also consumed, or were invaded by, the red or green algae. And the red or green algal cells became the chloroplasts of what are today the brown algae, diatoms, dinoflagellates, and euglenas. (Brown algae are the large seaweeds.) That is, brown algae, diatoms, dinoflagellates, and euglenas have chloroplasts that are cells inside of cells inside of cells. The chloroplasts of dinoflagellates even have little degenerated nuclei inside of them! Just as legless reptiles evolved several times, so did chloroplasts.
The evolutionary process tries endless combinations of mutations and adaptations, resulting in a living world that has much more variety that is hidden than variety that is obvious.