The domestic pig, Sus scrofa, is one of the world’s most recognizable farm animals, yet its deep evolutionary history holds surprising connections that rewrite the mammalian family tree. Pigs belong to the family Suidae, a group of mammals characterized by their omnivorous diet, thick skin, and distinctive snouts used for rooting. Genetic science has revealed a kinship that extends from the jungles of Africa to the depths of the ocean, tying the pig’s lineage to some of the planet’s largest and most aquatic creatures.
Defining the Pig Family Suidae
The family Suidae encompasses all true pigs, hogs, and boars. It is an Old World group, meaning its naturally occurring species are native to Europe, Asia, and Africa. Suidae is characterized by a stout body, thick hide, and a mobile snout supported by a prenasal bone and a cartilaginous disk. True pigs retain all four toes on each foot, though they primarily walk on the middle two digits.
The domestic pig is descended from the Eurasian wild boar, Sus scrofa, the most widespread member of the genus Sus. Other distinct genera within Suidae include the warthogs (Phacochoerus) found in African grasslands, known for their facial warts and upward-curving tusks. Another unique relative is the babirusa (Babyrousa) from Indonesian islands, distinguished by the male’s dramatically curved upper canine teeth that pierce the snout. This immediate family group highlights a diversity of form and habitat.
The Closest Evolutionary Relatives: Hippos and Peccaries
Immediately outside the true pig family, Suidae, are peccaries and hippopotamuses. Peccaries, or javelinas, belong to the family Tayassuidae and are often confused with pigs due to their similar appearance and rooting behavior. They are a distinct New World family native to the Americas. Peccaries differ from true pigs by having a more complex, two-chambered stomach and tusks that grow straight down. Genetic studies confirm that Suidae and Tayassuidae are sister-groups, sharing a common ancestor more recently than with any other mammal group.
The relationship with the hippopotamus, however, is a far more surprising connection revealed by modern molecular biology. Historically, pigs and hippos were grouped together due to their simple stomachs and low-crowned molar teeth. However, DNA analysis conclusively shows that hippos are not the next closest relative to pigs. Instead, genetic evidence places hippos as the closest living relative to the entire group of whales and dolphins, the Cetaceans.
This discovery means that pigs and peccaries form one distinct evolutionary branch (Suina), while hippos and cetaceans form a separate branch (Whippomorpha). The two groups, Suina and Whippomorpha, are considered sister-groups that share a common ancestor. The hippo’s superficial resemblance to a giant pig is a case of convergent evolution or shared ancestral traits rather than a close recent kinship.
Placing Pigs in the Mammalian Tree: Ruminants and Cetaceans
Pigs, along with all hoofed animals and whales, are classified under the order Artiodactyla, which is now often referred to as Cetartiodactyla to include the cetaceans. This order groups the even-toed ungulates with their aquatic relatives, a classification driven entirely by genetic evidence.
Within this massive order, pigs and peccaries are part of the suborder Suina, and they represent one of the earlier branching points in the Artiodactyla tree, second only to the camel family (Tylopoda). The next major division splits into the Whippomorpha (hippos and whales) and the Ruminantia, a suborder that includes familiar animals like cattle, deer, goats, and sheep.
The unexpected connection to whales is the result of a shared common ancestor that lived approximately 60 million years ago. While pigs evolved to thrive as land-dwelling omnivores, the lineage leading to hippos and whales split off and adapted to aquatic life. The shared Artiodactyla classification means that the pig’s deep family tree includes animals that chew cud and others that navigate the open ocean, demonstrating the incredible diversity that can arise from a single ancient ancestor.