- "Humans are dumb and they die easy."
Humans (taxonomic designation: "Homo sapiens") are a form of sapient mammal beings from the planet Earth. Thеy are the dominant species of Earth, Mars, and possibly other planets. Some and robots hate them because of the fact that humans always want to be in positions of power.
On Earth normally lives one species of human: Homo Sapiens, until the event in "Fun on a Bun".
Modern Humans (Homo Sapiens Sapiens)
Most of the people living in 31st century at Earth. For thousands of years, they lived next to technology as opposed to their cousins. When they first time met them in prehistoric times, they treated them as second-class humans and didn't want to interbreed with them, as these seconds offered.
Neanderthals (Homo Sapiens Neanderthalensis)
Until recently, they lived under the ice cover since 30,000 years with the flora and fauna of ice age period, in Germany. When they got out to the surface under the leadership of Fry, wished to take revenge for their species' discrimination by modern humans. When they saw Fry (who, due to temporary head trauma, bore a resemblance to a Neanderthal) kissing Leela, they thought that the period of discrimination was over. They then claimed that they could coexist with Homo sapiens, and joined the Oktoberfest celebration; it is probable that they subsequently began to live together with them on the surface.
The only thing different from modern man is their lower brow and thicker forehead bone.
For a full list, see the list here.