You are using an older browser version. Please use a supported version for the best MSN experience.

Why Whales Got So Big

The Atlantic logo The Atlantic 08-04-2018 Ed Yong

FILE-This Oct. 11, 2017 file photo shows a Southern right whale breach in El Doradillo Beach, Patagonia, Argentina. Scientists watching for baby right whales off the Southeast U.S. coast have yet to spot a single newborn seven weeks into the endangered species' calving season , a dry spell researchers haven't seen in nearly 30 years. (AP Photo/Maxi Jonas, File) © Catalyst Images FILE-This Oct. 11, 2017 file photo shows a Southern right whale breach in El Doradillo Beach, Patagonia, Argentina. Scientists watching for baby right whales off the Southeast U.S. coast have yet to spot a single newborn seven weeks into the endangered species' calving season , a dry spell researchers haven't seen in nearly 30 years. (AP Photo/Maxi Jonas, File) Editor's note: The opinions expressed in this article are those of the author on behalf of our content partner and do not represent the views of MSN or Microsoft

The first time I came face to face with a sea lion, I nearly screamed. I was snorkeling, and after a long time spent staring down at colorful corals, I looked up to see a gigantic bull, a couple of feet in front of my mask. Its eyes were opalescent. Its long canines hinted at its close evolutionary ties to land-based predators like bears and dogs. And most unnervingly of all, it was huge.

Mammals tend to get that way when they invade the ocean. The pinnipeds—seals, sea lions, and walruses—tend to be immense blobs of muscle and blubber. The same could be said for manatees and dugongs. And whales are almost synonymous with bigness. Time and again, lineages of furry mammals have gone for a swim and over evolutionary time, they’ve ballooned in size. Why?

CORRECTS LOCATION FROM PENINSULA VALDES TO EL DORADILLO BEACH - In this Oct. 11, 2017, a Southern right whale glides in the waters of the El Doradillo Beach, Patagonia, Argentina. A record number of Southern right whales migrate each year from Antarctica to Argentina's Patagonia to give birth and feed their offspring. (AP Photo/Maxi Jonas ) © Catalyst Images CORRECTS LOCATION FROM PENINSULA VALDES TO EL DORADILLO BEACH - In this Oct. 11, 2017, a Southern right whale glides in the waters of the El Doradillo Beach, Patagonia, Argentina. A record number of Southern right whales migrate each year from Antarctica to Argentina's Patagonia to give birth and feed their offspring. (AP Photo/Maxi Jonas )

Most of the explanations for this trend treat the ocean as a kind of release. The water partly frees mammalian bodies from the yoke of gravity, allowing them to evolve heavy bodies that they couldn’t possibly support on land. The water unshackles them from the constraints of territory, giving them massive areas over which to forage. The water liberates them from the slim pickings of a land-based diet and offer them vast swarms of plankton, crustaceans, and fish to gorge upon.

But William Gearty from Stanford University has a very different explanation. To him, the ocean makes mammals big not because it relieves them of limits, but because it imposes new ones.

“As you enter the water, you start to lose heat from your body that you aren’t losing on land or air,” he explains. To counteract that constant loss of heat, humans use wet suits, whales have blubber, and otters have thick fur. “But really the easiest way to counteract it is to get bigger,” Gearty says. As bodies balloon, volume increases faster than surface area does, so you produce more heat in your body but lose comparatively less of it from your skin. But animals can’t become infinitely big because larger bodies also demand more fuel. There’s only so much food that an animal can reasonably find, catch, and swallow.

CORRECTS LOCATION FROM PENINSULA VALDES TO EL DORADILLO BEACH - In this Sept. 26, 2017 photo, a Southern right whale swims on the surface near the coast of El Doradillo Beach, Patagonia, Argentina. A record number of Southern right whales migrate each year from Antarctica to Argentina's Patagonia to give birth and feed their offspring. (AP Photo/Maxi Jonas ) © Catalyst Images CORRECTS LOCATION FROM PENINSULA VALDES TO EL DORADILLO BEACH - In this Sept. 26, 2017 photo, a Southern right whale swims on the surface near the coast of El Doradillo Beach, Patagonia, Argentina. A record number of Southern right whales migrate each year from Antarctica to Argentina's Patagonia to give birth and feed their offspring. (AP Photo/Maxi Jonas )

So, the need to stay warm sets a floor for the body size of oceanic mammals, while the need to eat sets a ceiling. And the gap between them, Gearty found, is surprisingly narrow—and far more so than on land.

Together with Jonathan Payne, also from Stanford, and Craig McClain from the Louisiana Universities Marine Consortium, Gearty collected data on the sizes of almost 7,000 mammal species, both living and extinct. He showed that the marine groups—whales, manatees, and seals—have all independently hit an average optimum mass of around 1,100 pounds.

There’s obviously a lot of variation around that—a sperm whale is clearly not the same size as a dolphin. But crucially, that variation is much lower in the sea than it is on land. “The minimum size in these aquatic groups is thousands of times larger than the minimum for terrestrial groups, but the maximum size is only 25 times larger,” says Gearty. “I found it strange that no one had noticed before.”

In this Sept. 2017, photo made with a drone, a young resident killer whale chases a chinook salmon in the Salish Sea near San Juan Island, Wash. The photo, made under a National Marine Fisheries Service (NMFS) permit, which gives researchers permission to approach the animals, was made in collaboration with NOAA Fisheries/Southwest Fisheries Science Center, SR3 Sealife Response, Rehabilitation, and Research and the Vancouver Aquarium's Coastal Ocean Research Institute. Endangered Puget Sound orcas that feed on chinook salmon face more competition from seals, sea lions and other killer whales than from commercial and recreational fishermen, a new study finds. (John Durban/NOAA Fisheries/Southwest Fisheries Science Center via AP) © Catalyst Images In this Sept. 2017, photo made with a drone, a young resident killer whale chases a chinook salmon in the Salish Sea near San Juan Island, Wash. The photo, made under a National Marine Fisheries Service (NMFS) permit, which gives researchers permission to approach the animals, was made in collaboration with NOAA Fisheries/Southwest Fisheries Science Center, SR3 Sealife Response, Rehabilitation, and Research and the Vancouver Aquarium's Coastal Ocean Research Institute. Endangered Puget Sound orcas that feed on chinook salmon face more competition from seals, sea lions and other killer whales than from commercial and recreational fishermen, a new study finds. (John Durban/NOAA Fisheries/Southwest Fisheries Science Center via AP)

These trends aren’t consistent with the idea of the ocean as a release. Instead, it suggests that the water imposes strict constraints. To thrive in it, mammals must be just the right size—big, yes, but not too big and not too small. And Gearty could calculate the boundaries of this Golidlocks zone with a set of equations that connect a mammal’s size with the heat it loses to the water and the rate at which it can find food. These equations predicted both the optimum 1,100-pound average that seagoing mammals have evolved toward, and the narrow range of sizes around that ideal.

That makes sense, says Samantha Price from UC Davis, who studies mammal evolution. “But evolution is complex,” she says, “and energetic trade-offs may not have driven the evolution of large size in complete isolation.” It’s possible that the other proposed factors, like increased buoyancy, made it easier for marine mammals to hit that Goldilocks zone, by reducing the costs of being larger.

In this Wednesday March 28, 2018 photo, a North Atlantic right whale feeds on the surface of Cape Cod bay off the coast of Plymouth, Mass. North Atlantic right whales are facing the threat of extinction within a generation, and the movement to preserve them is trying to come up with new solutions. (AP Photo/Michael Dwyer) © Catalyst Images In this Wednesday March 28, 2018 photo, a North Atlantic right whale feeds on the surface of Cape Cod bay off the coast of Plymouth, Mass. North Atlantic right whales are facing the threat of extinction within a generation, and the movement to preserve them is trying to come up with new solutions. (AP Photo/Michael Dwyer)

And as always in biology, there are exceptions. Sea otters, for example, are unusually small for marine mammals—they’re about as big as a Labrador. That might be because their extremely thick fur, with up to a million hairs per square inch, allows them to stay warm without being big. They also spend a lot of time on land, where heat loss is less of a problem.

At the other extreme, the baleen whales go way beyond the 1,100-pound optimum. The biggest of them, the blue whale, can reach up to 380,000 pounds. It and its truly gargantuan relatives only emerged in the last few million years of whale evolution, and Nick Pyenson from the Smithsonian Institution thinks he knows why. Around 3 million years ago, a combination of changes to glaciers, winds, and currents created large surges of nutrients in coastal waters, which then fed hordes of crustaceans and small fish—potential prey for whales. But as I wrote last year:

These bonanzas weren’t evenly distributed. They were concentrated in particular, far-flung places—all-you-can-eat buffets separated by literal food deserts. And that, Pyenson says, is why the giant baleen whales evolved. They are beautifully adapted to hunt down sparse but concentrated prey. Their huge size allows them to survive for long stretches without encountering any food. And they evolved a foraging technique called lunge-feeding, where they accelerate into a shoal of prey, open their ballooning mouths, and suck in vast volumes of water.

The emergence of concentrated prey, and the evolution of a technique for capturing them, allowed whales to smash through the diet-imposed ceiling that keeps other marine mammals big, but not too big. That's why they, rather than manatees or seals, transformed from big animals into the biggest animals that ever existed.

Related: Facts to know about whales [Photo Services]

There she blows: Facts to know about whales

More from The Atlantic

image beaconimage beaconimage beacon