Pigs and hippopotamuses resemble a human body in many ways, including body fat distribution, cover of hair and size of many internal organs. For this reason pigs are used for medical research, and are known as a Translational Research Model. If something works in a pig it has a higher possibility of working in a human. These similarities do not mean that we are closely related to pigs. Modern comparison of DNA sequences of different mammals show that we are most closely related to mice than we are to pigs, we are only have similarity to pigs because of Convergent Evolution.
Convergent evolution is when mutations of DNA encourage a species diverge or converge because of environment or food sources. There are two species otters, the river otters spend their time on land near river banks feeding on small mammals, birds, frogs and fish from the river whilst sea otters spend all their time in the sea and by mutating slightly acquired a shorter flatter tail which have given them the ability to dive as deep as 250 feet (76.2 mtr) enabling them to feed on a bountiful supply of sea urchins, clams, mussels and crabs and so becoming two to three times the size of river otters. The two species have diverged from each other.
An amazing example of evolutionary convergency is that between sharks and whales. Sharks are among earths most ancient creatures, evolving over 445 million years ago, long before any land animal or even trees. They commanded a niche that has served all their requirements and with not having many mutations had no reason to change. Whales on the other hand went through the many mutations that all mammals went through to become fish, amphibious and then land mammals. But small whales, much like otters, started to diverge from their original mammal ancestor and fully mutated and evolved into sea mammals, becoming larger and larger through the various species of whales and dolphins until they became so large that they were not nimble enough to hunt prey. Sharks had the same problem, so we have the situation that the two largest creatures that have ever existed on earth, larger than the biggest Dinosaurs, live by cruising through the oceans with their mouths open and filtering out tiny krill and plankton.
Coincidentally, the ancient ancestors of whales were pigs and hippos.