Let's compare a human baby with the offspring of a Northern Elephant Seal. The former gains weight at the rate of an ounce or less per day, while the latter -- well, we're talking pounds now, not ounces.
A Northern Elephant Seal enters the world weighing a modest 75 pounds. It then spends much of the next month nursing, and by the time it takes its last drink of milk the pup tips the scales at a respectable 400 pounds. That's about 10 pounds of new elephant seal every day.
The reason the seal can pack it on so quickly is that the milk it's drinking is the richest in fat of any mammal -- it's more than 50 percent fat. Human milk, by contrast, contains less than 10 percent fat. Even whipping cream -- 35 percent fat -- is dietetic by comparison.
Click here for an up-close picture of a Northern Elephant Seal family.