Ichthyosaurs (there were many types) were streamlined creatures with long snouts, large eyes, and a powerful tail. Later fossils would show that they had a large dorsal fin on their back. They sped through the seas of the Jurassic (and Triassic, and Cretaceous) racing after fish and shellfish. If one were to pop up off the Dorset shore today, observers on land might well believe that they were watching a dolphin as the animal dashed and jumped among the waves. But Ichthyosaurs were not related to dolphins. They were reptiles, members of a family that originated from lizard-like ancestors instead of the land-dwelling mammals that produced dolphins and whales.

The reason that Ichthyosaurs look much like dolphins is because both are performing the same role in a similar environment. Both are predators that hunt their prey in the ocean. The large eyes come because sea water is clear and sight is an important aspect of tracking and capturing fast-moving fish in shallow water (those few species of dolphins that live in the muddy waters of rivers are either nearly or completely blind). The long snout filled with banks of sharp, narrow teeth is an excellent mechanism for catching fish. Most of all, both had the same major problem — moving quickly and efficiently through water.

The ease with which an object can move through a medium like air or water is measured by looking at the drag coefficient. A high drag coefficient means that an object is not very efficient at moving through the medium, and will need to expend more energy. A person walking in air has a drag of about 1.2 (which is not particularly good). Older cars have drag coefficients as high as 0.7. The Toyota Prius and the Honda Insight both have drag coefficient below 0.3. That's not bad. The most streamlined supersonic aircraft manage a drag less than 0.02 — they give up only about one fifteenth as much energy to pushing aside the air as even a highly efficient car.

But water is 830 times as dense as air, so the penalty for a water-going creature that isn't shaped to avoid drag is 830 times higher. The drag coefficient for dolphins is less than 0.004 — much better than the sleekest aircraft. Ichthyosaurs looked a lot like dolphins because dolphins are a pretty good design for moving in water. Both animals were refined by the same powerful forces: the need to defeat drag... and the idea first fully realized by Charles Darwin and Alfred Russell Wallace.

Two types of organisms moving toward similar solutions to the same problem, despite having very different origins, is a common feature of the fossil record (and of the living world around us). Bats and pterosaurs had very different ancestors, but made some of the same adaptations to flying. Marsupial animals in Australia developed many of the same solutions to existence as their placental relatives in the rest of the world, leading to informal designations of some Australian natives as the "marsupial mouse" or "marsupial cat" or "marsupial wolf."

Both creatures and consumer products adapt to an "environment." For the first it can be something as simple as the medium through which they move, but it's also the food they search for, the predators that hunt them, the temperature of the water, the chemistry of the air, their competitors, their diseases — everything around them. Likewise, products exist in an environment that includes consumers, competitors, retail markets, economic conditions, resource availability, and items as ephemeral as "style."

Ideas also form in an environment. They require a foundation of previous ideas, the availability of raw information, and a society that supports new thinking. In 1684, German mathematician Gottfried Leibniz published the first paper based on calculus, which he had invented over the previous decade. Meanwhile Isaac Newton didn't publish his first work of calculus until 1693, but said he had been working on his version since 1666. For three centuries, adherents of both men have argued over who really invented calculus, but there's no reason to believe the answer isn't both. On the technological front, the list of near simultaneous discoveries is lengthy. Was the first practical electric light bulb invented by Thomas Edison, or Joseph Swan? Did Alexander Bell invent the telephone, or was it Elisha Gray? The radio, the television, and the MRI imager all have multiple claimants to the title of "inventor of." Even when it comes to relativity, there are several others who anticipated at least some part of what Einstein would so brilliantly assemble.

When Charles Darwin opened a note from Alfred Russell Wallace in the spring of 1858 and found that Wallace had deduced the same ideas on natural selection that Darwin had been thinking over since 1837, it wasn't too surprising. Both men had been inspired by reading the Reverend Thomas Malthus, whose 1798 essay fretted over the possibility of the human population outracing its food supply.

The power of population is indefinitely greater than the power in the earth to produce subsistence for man. Population, when unchecked, increases in a geometrical ratio. Subsistence increases only in an arithmetical ratio.A slight acquaintance with numbers will show the immensity of the first power in comparison with the second.

Malthus limited his speculations to man, but both Darwin and Wallace began to think about what the limits of population meant for other species. If any creature expanded its population generation by generation, it must inevitably run into limits. Limits on food. Limits on space. Limits on the proper kind of habitat. In fact, most creatures must be at that limit all the time, with the environment supporting as many as possible.

Both Darwin and Wallace knew that there were differences between individuals. That was clear in the observations of animals and plants they had made on their travels. It was equally obvious from the domestic animals they saw all around them. Thinking of Victorian England today, the idea that the streets of London were full of horses seems odd — and somewhat charming. But those streets were also full of sheep, goats, cows, chickens, and other animals. With no refrigeration, thousands of animals were slaughtered every day throughout the city. Cages of birds, pens of animals, rooms of houses turned into makeshift stockyards, slaughterhouses and butcher shops where blood ran into gutters were also standard features of most London neighborhoods. Which seems a good deal less charming. Even people who didn't live on farms were constantly exposed to domesticated animals of all types. Which is a large part of why both Darwin and Wallace made extensive use of domesticated animals as examples in their work.

And that's all the ingredients there are for natural selection. Limits on population put a pressure on which organisms hang around and reproduce. Not all organisms of the same species are identical. Those that live, love, and have offspring, tend to pass their traits to the next generation.

Populations of organisms can, and do, contain many variations all the time. Often the variations they carry don't have any effect on their ability to produce offspring. Is a blue-eyed wolf more likely to have pups than a grey-eyed wolf? Only if the wolf's potential partners have a thing for a certain eye color. When conditions are good, many traits have such a minimal effect on reproduction that they linger in the populace. What does it matter if you're able to skate by on less food when food is abundant? Until it's not.

A change in any aspect of the environment can suddenly turn what had been just another variant into either an advantage or a detriment. Being able to survive on less water might not be valued, until there's a prolonged drought. Tolerating heat or cold better than your neighbors might have no value, until extreme conditions strike. Being the fastest rabbit in the area might not matter, until faster foxes arrive. Big can be big when there's plenty of food, until shortages turn small into an edge.

There are differences among individuals. Some of those differences tend to be inherited by the offspring produced by those individuals. If there is a selective pressure that acts against those differences, you get evolution. The end. In any given generation, the differences may be small. The edge given to one variant over another can be razor thin. Still, evolution moves on, aided by that secret ingredient spelled out by James Hutton — deep time.

The simplicity of the idea is part of what made it hard for some people to accept. There were scientists among Darwin's immediate circle of friends who knew that evolution had happened, but who thought Darwin's mechanism was just not sufficient. There had to be more to it. Over the next sixty years, natural selection would come in and out of favor as the driving system behind evolution, and that bald simplicity would be one of the biggest problems. Even in Darwin's time, his most vocal opponents were not those who didn't believe that evolution had taken place, it was those — like anatomist Richard Owen, who had worked with Darwin on specimens returned from the Beagle — who didn't believe that Darwin's simple process could be responsible for all the variety in the world.

However, this simplicity was also one of the theory's biggest assets. Once explained -- and Darwin couched the idea expertly, with many examples and answers to the questions he anticipated from opponents -- there was a forehead smack heard round the world. Many who had been followers of some earlier system, or doubters of evolution altogether, saw the unmistakable nature of the idea and became vocal supporters.

Thomas Huxley's reaction was probably typical of many who read On the Origin of Species when it reached the stands in 1859.

"How extremely stupid not to have thought of that!" -- Thomas Huxley

Huxley could have thought of it. So could any one of hundreds of naturalists who had backgrounds, experience, and information similar to that held by Darwin and Wallace. The many examples of animals and plants that Wallace had cataloged in his Malaysian wanderings and Darwin had seen in his shipboard travels, gave them both an important nudge toward thoughts of natural selection. But others had seen as much and done as much. Certainly men like Huxley, who had also been part of a round-the-world scientific voyage and had access to the same data that Darwin had used, or men like Owen, who had examined and cataloged tens of thousands of creatures both fossil and living, could have come up with the same idea.

That they didn't only shows how hard simple things can be. Natural selection looks simple, and it is simple, but out of that simplicity endless complexity can be generated. Looking at the world, most scientists (and non-scientists) saw only the complexity. The living world was so massive, so intricately interwoven, so complex, that people looked for massive, intricate, complex answers. The real insight that Darwin and Wallace shared was that complexity could spring from simplicity. There was no need to go looking for a complex solution. There was no need for divine intervention at the appearance of every species, and no need for a mechanism that propelled the world toward some hidden plan.

In fact, for all their apparent similarities, Darwin and Wallace reached their similar conclusions from different directions. Darwin, despite originating an idea that's the most powerful in all of science, was something of a conservative thinker. The words of his textbooks and professors put him on a path where he gradually, almost tentatively, moved toward the idea of natural selection, and then spent decades expanding, testing, and validating his thoughts. Wallace was the real radical, a man who welcomed odd thoughts and unorthodox notions. Wallace would go on to not only elaborate on natural selection, but also to note that many animals employed "warning colors" to announce that they carried poison or some similar threat. He would be the father of biogeography, doing much more than Darwin to explain and establish the distribution of plants and animals. He would also be a spiritualist who attended seances and supported channelers. Wallace was something of a scientific James Dean — if there was a traditional thought, he had a rebellion.

Both men were brilliant. Both were capable of highly original thinking. But Darwin was persistent, dogged, and obsessive when it came to working out every implication of an issue. Wallace was more mercurial, always ready to tackle something new. The two men came together on natural selection because they were driven there by the data. Once glimpsed, the idea of natural selection was as powerful and necessary for them both as the streamlined bodies of the dolphin and the ichthyosaur. Some ideas are so compelling that they shape the direction of the whole world.

Some people are equally compelling. A decade before Wallace's letter arrived in Darwin's mailbox, the Geologic Society realized that they had to do something to recognize one of the most important paleontologists in the nation — Mary Anning. The woman who had started by selling fossils to support her family had continued at the work all her life. The beautiful specimens she recovered, among the most complete ever found, provided additional proof of extinction and showed how different the seas of the Jurassic had been. She had uncovered not only the ichthyosaur, but multiple forms of the long-necked plesiosaurs, extinct fish, crocodiles, and even a beautiful pterosaur that had been unlucky enough to plunge into the ancient sea.

Anning sold her discoveries to the men like Richard Owen who described them and gained fame in the process, but Mary was never more than a step away from poverty. Still, the importance of what Anning had done and the dedication with which she pulled out one complete skeleton after another won her admiration among the men who were rewriting science. In 1847 the Geological Society was, like all such societies at the time, restricted to men only, but by overwhelming vote they made Mary Anning an honorary member. Only a few months later she died of breast cancer at the age of 47. On her death, a stained glass window as erected in the church of St. Michael the Archangel. The inscription on the window read "This window is sacred to the memory of Mary Anning of this paris, who died 9 March 1847 and is erected by the vicar and some members of the Geological Society of London in commemoration of her usefulness in furthering the science of geology, and her benevolence of heart and integrity of life."

The window shows how valued Anning's contributions were, but there's another remembrance of Mary Anning that's perhaps an even better claim to fame — though it's not quite "parallel" to a stained glass window. Mary Anning, the child who sold fossils on the beaches of Dorset to save her impoverished family, is said to be the inspiration behind the old tongue-twister "She sells sea shells by the sea shore."