evolution



Evolution by natural selection is one of the best substantiated theories in the history of science, supported by evidence from a wide variety of scientific disciplines, including paleontology, geology, genetics and developmental biology.

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The theory has two main points, said Brian Richmond, curator of human origins at the American Museum of Natural History in New York City. “All life on Earth is connected and related to each other,” and this diversity of life is a product of “modifications of populations by natural selection, where some traits were favored in and environment over others,” he said.

More simply put, the theory can be described as “descent with modification,” said Briana Pobiner, an anthropologist and educator at the Smithsonian Institution National Museum of Natural History in Washington, D.C., who specializes in the study of human origins.

The theory is sometimes described as “survival of the fittest,” but that can be misleading, Pobiner said. Here, “fitness” refers not to an organism’s strength or athletic ability, but rather the ability to survive and reproduce.

Origin of whales

In the first edition of “The Origin of Species” in 1859, Charles Darwin speculated about how natural selection could cause a land mammal to turn into a whale. As a hypothetical example, Darwin used North American black bears, which were known to catch insects by swimming in the water with their mouths open:

“I can see no difficulty in a race of bears being rendered, by natural selection, more aquatic in their structure and habits, with larger and larger mouths, till a creature was produced as monstrous as a whale,” he speculated.

The idea didn’t go over very well with the public. Darwin was so embarrassed by the ridicule he received that the swimming-bear passage was removed from later editions of the book.

Scientists now know that Darwin had the right idea but the wrong animal: Instead of looking at bears, he should have instead been looking at cows and hippopotamuses.

The story of the origin of whales is one of evolution’s most fascinating tales and one of the best examples scientists have of natural selection.

The last shore-dwelling ancestor of modern whales was Sinonyx, top left, a hyena-like animal. Over 60 million years, several transitional forms evolved: from top to bottom, Indohyus, Ambulocetus, Rodhocetus, Basilosaurus, Dorudon, and finally, the modern humpback whale.
The last shore-dwelling ancestor of modern whales was Sinonyx, top left, a hyena-like animal. Over 60 million years, several transitional forms evolved: from top to bottom, Indohyus, Ambulocetus, Rodhocetus, Basilosaurus, Dorudon, and finally, the modern humpback whale.
Credit: NOAA
Natural selection

To understand the origin of whales, it’s necessary to have a basic understanding of how natural selection works. Natural selection can change a species in small ways, causing a population to change color or size over the course of several generations. This is called “microevolution.”

But natural selection is also capable of much more. Given enough time and enough accumulated changes, natural selection can create entirely new species, known as “macroevolution.” It can turn dinosaurs into birds, amphibious mammals into whales and the ancestors of apes into humans.

Take the example of whales — using evolution as their guide and knowing how natural selection works, biologists knew that the transition of early whales from land to water occurred in a series of predictable steps. The evolution of the blowhole, for example, might have happened in the following way:

Random genetic changes resulted in at least one whale having its nostrils placed farther back on its head. Those animals with this adaptation would have been better suited to a marine lifestyle, since they would not have had to completely surface to breathe. Such animals would have been more successful and had more offspring. In later generations, more genetic changes occurred, moving the nose farther back on the head.

Other body parts of early whales also changed. Front legs became flippers. Back legs disappeared. Their bodies became more s

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