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Evolution of Whales
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By Douglas H. Chadwick Photographs by Robert Clark

Earth’s largest animals are sometimes born with a leg or two, a startling genetic reminder of the time, 50 million years ago, when their ancestors walked on dry land.

Get a taste of what awaits you in print from this compelling excerpt.

The coast of southern Alaska grows glaciers and brooding rain forests. Hot weather is rare, but since sunup the day had brought nothing else. By afternoon everyone was sweltering. The first person to do more than just talk about leaping off the boat into iceberg-chilled Frederick Sound performed a cannonball. Others jackknifed and belly flopped in. This contest to raise the biggest splash was spirited but short. No sooner had the last person shivered back aboard than three humpback whales surfaced exactly where the jumpers had been landing. The whales lingered a while, misting the crew with spray from their blowholes, then eased down out of sight.

We were still exclaiming about the visit minutes later when the sea to starboard erupted. A 45-foot (14-meter) whale went skyborne up to its tail. Then a pair leaped in near synchrony. Shwa-boom! Ker-bloosh! Others started to breach on all sides. For the next half hour humpbacks were flying and crash landing, sending out minor tsunamis, floating head down to whap the water with their tail flukes, and lying on their sides to slap the surface with long pectoral fins.

It would be the height of arrogance to think we inspired 40-ton (40,000-kilogram) organic submarines to compete with us. But I saw what I saw. Whales have a way of making the incredible real; their very name has become a metaphor for something almost too big to get our minds around. I wondered what the crews on whaling ships thought when they would occasionally haul aboard a fully grown adult with miniature legs sticking out from its flanks. Whether they knew it or not, they were looking at testimony to the origin of these mysterious marine giants.

More than 80 living species of mammals are classified as whales, or, as taxonomists say, cetaceans (from ketos, the Greek name for sea monster). They can be divided into two groups. Mysticetes, or baleen whales, use comb-like plates hanging from the roofs of their mouths to strain food from seawater. Blue whales, fin whales, bowheads, and most of the other real titans belong to this division along with smaller types such as minke whales and pygmy right whales. Odontocetes, or toothed whales, include belugas, narwhals, sperm whales, pilot whales, and beaked whales—plus all the dolphins and porpoises. We call the largest dolphins killer whales.

But what did the first whales look like? And what gave rise to them? For a long time scientists could only speculate, for the oldest fossils anyone knew of had already assumed the basic appearance of whales. In the absence of intermediate forms, people proposed almost every type of mammal as ancestors.

At last a series of fossil discoveries has unveiled whales’ distant past. Paleontologists can suddenly trace the most colossal animals ever to appear on Earth step-by-step back to their beginnings early in the Eocene epoch, often referred to as the dawn of the age of mammals, which lasted from about 55 million to 34 million years ago.

Get the whole story in the pages of National Geographic magazine.

It took millions of years for whales to evolve from walking land animals into the water-dwelling creatures of today. How are humans still evolving? Tell us what you think.

In More to Explore the National Geographic magazine team shares some of its best sources and other information. Special thanks to the Research Division.

An ancient group of ungulates (animals that possess hooves, like horses and pigs) called mesonychids have long been thought to have given rise to the earliest whales and, subsequently, to modern whales. But the recent fossil discovery of two new species point whales back to an altogether different group of hoofed creatures called artiodactyls.

Discovered by University of Michigan paleontologist Philip Gingerich and a team of colleagues, artiodactyls have an even number of hoofed toes and include pigs, hippos, and ruminants such as cows. Molecular evidence from the analyses of proteins indicates that the hippopotamus is the closest kin to modern whales.

The team’s findings are described in the Sept. 21, 2001 issue.

—David A. O’Connor

Hans Thewissen Laboratory
This website provides information about the evolution of whales and the ongoing research by Hans Thewissen, one of the paleontologists featured in our article.

University of California, Berkeley, Museum of Paleontology
The site provides general background information about the cetaceans and their evolution.

Whale and Dolphin Conservation Society
A comprehensive guide to the living species of the order Cetacea can be found at this website.

Dolphin Research Center
This site focuses on the evolution and general biology of dolphins.

Buena Vista Museum Web Site
Here you will find more information about Sharktooth Hill and the rich fossil bed mentioned in our article.


Gingerich, Philip D., and others. “Origin of Whales From Early Artiodactyls: Hands and Feet of Eocene Protocetidae From Pakistan,” Science (September 21, 2001) 2239-2242.

Berta, Annalisa, and James L. Sumich. Marine Mammals: Evolutionary Biology. Academic Press, 1999.

Carwardine, Mark, ed. Whales, Dolphins and Porpoises, 2nd ed. Checkmark Books, 1999.

Gingerich, Philip D., B. Holly Smith, and Elwyn L. Simons. “Hind Limbs of Eocene Basilosaurus: Evidence of Feet in Whales.” Science, Vol. 249 July 13, 1990, 154–156.

Gingerich, Philip D., and Mark D. Uhen. “Likelihood Estimation of the Time of Origin of Cetacea and the Time of Divergence of Cetacea and Artiodactyla.” Available online at

Norman, David. Prehistoric Life: The Rise of the Vertebrates. Macmillan, 1994.

Simamura, Mitsuru, and others. “Molecular Evidence From Retroposons That Whales Form a Clade Within Even-Toed Ungulates.” Nature, vol. 388, Aug. 14, 1997, 666-670.

Zimmer, Carl. At The Water’s Edge: Macroevolution and the Transformation of Life. The Free Press, 1998.


Ascher-Walsh, Rebecca. “Keiko’s Journey,” World (May 2001), 14-17.

Chadwick, Doughlas H. “Pursuing the Minke: The Most Abundant Baleen Whale Is Still a Mystery to Scienc—and a Target for Whalers,” National Geographic (April 2001), 58-71.

Chadwick, Doughlas H. “Blue Refuges: U.S. National Marine Sanctuaries,” National Geographic (March 1998), 2-31.

Nathan, Amy. “Swimming With Giants,” National Geographic World (December 1997), 32-36.

Whitehead, Hal. “The Realm of the Elusive Sperm Whale,” National Geographic (November 1995), 56-73.

Norris, Kenneth S. “Beluga: White Whale of the North,” National Geographic (June 1994), 2-31.

Payne, Roger. “Humpbacks: Their Mysterious Songs,” National Geographic (January 1979), 18-25.

Tarpy, Cliff. “Killer Whale Attack!” National Geographic (April 1979), 542-545.

Grosvenor, Donna K. The Blue Whale, National Geographic Books, 1977.

Portrait of a Whale, National Geographic Videos, 1976.

Walker, Theodore J. “The California Gray Whale Comes Back,” National Geographic (March 1971), 394-415.


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