Birds as big as elephants, tortoises the size of small cars, rats the size of dogs—what causes some animals to grow so huge? Gigantism is caused by environmental conditions that allow the animals to grow virtually without limits. There are many examples of gigantism in the animal kingdom, from reptiles and rodents to mammals and birds.
Gigantism happens when animals are relatively isolated, like on islands or in the ocean. If the animals have a good supply of food and few natural predators, there is nothing to stop them from growing to gigantic proportions. For example, the Galapagos giant tortoise routinely weighs in at more than 500 pounds. The largest one on record was nearly 900 pounds. And the planet's largest giant, the blue whale, reaches up to 100 feet and weighs up to 200 tons.
-Excerpted from "The Ascent of Mammals" by Darlene Darwin
Which information is implicit in the passage?
The blue whale is the planet's largest giant animal.
Predators usually become giant animals.
Predators usually prevent animals from growing to giant proportions.
Gigantism occurs when animals live in isolated areas.
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