A massive, semiaquatic African mammal — the third-largest land animal after elephants and rhinos, with surprisingly close evolutionary ties to whales and a reputation as one of Africa's most dangerous animals.
“River horse”
The name “hippopotamus” comes from the Greek hippos (horse) + potamos (river) — “river horse.” The animal isn’t actually closely related to horses; the Greek namers were going by superficial similarity in size and bearing. Modern phylogenetic research shows hippopotamuses are actually most closely related to whales and dolphins — they share a common ancestor about 55 million years ago.
That common ancestor was a small semi-aquatic herbivore. Hippos stayed in fresh water; whales returned to the sea and lost their hindlegs. The relationship is one of the more counterintuitive findings of molecular phylogeny.
Africa’s deadliest large animal
Hippos are responsible for an estimated 500 human deaths per year in Africa — more than lions, leopards, elephants, or buffalo. They’re aggressive, especially:
- Mothers protecting calves
- Males defending territory in water
- Animals encountered between river and grazing land at night
A hippo can run up to 30 km/h on land and bite with a force estimated at 8,000 newtons (about four times a human bite). Their canine teeth grow continuously and reach 50 cm in length. Boats and small canoes are particularly vulnerable in hippo-frequented waters.
A skin chemistry puzzle
Hippo skin secretes a reddish fluid sometimes mistakenly called “blood sweat.” It’s neither sweat nor blood — it’s a unique secretion containing two pigments (one red, one orange) that act as natural sunscreen, antibiotic, and moisturizer. The compounds protect hippo skin from sunburn and bacterial infection during the long hours each day spent in tropical water and direct sun.
The chemistry has been studied for potential cosmetic and pharmaceutical applications, though no commercial product has emerged.
Underwater grace
Hippos can’t actually swim well. They walk along the bottoms of rivers and lakes, holding their breath for 5–6 minutes per dive. Even calves have an instinct to walk underwater rather than paddle.
The eyes, ears, and nostrils sit on the top of the head — a feature shared with crocodiles — letting the animal see and breathe while almost fully submerged. Special glands close the nostrils and ears underwater.
A two-species genus
The familiar hippopotamus has a smaller relative: the pygmy hippopotamus (Choeropsis liberiensis) of West African rainforests. Pygmy hippos are about a quarter the weight of common hippos, more solitary, and rarer — fewer than 3,000 remain in the wild. They’re listed as Endangered.
A modern feral population
Pablo Escobar imported four hippos to his estate in Colombia in the 1980s. After his death, the animals escaped into local rivers and bred. Today, an estimated 150–200 hippos live wild in the Magdalena River — the largest invasive hippo population outside Africa, with no natural predators and no checks on their growth. Colombian wildlife authorities are debating sterilization, relocation, or culling. The “cocaine hippos” are now an ecological problem.