The cast of 'Jersey Shore' aside, there's pretty much only one kind of human being these days -- but according to a new scientific discovery, it may not have always been that way.

For a long time, we've believed the most primitive member of our lineage was the Homo erectus. But about 50 years ago, scientists in Tanzania found evidence of an even earlier species, dubbed the Homo habilis, which had a smaller brain and an apelike skeleton.

More recently, fossils estimated to be 1.7 and 1.9 million years old were discovered in Kenya, and the so-called Homo rudolfensis had a larger brain and a flatter face -- suggesting not only that early humans were quite diverse, but that more than one type may have walked the earth during the same time period.

But some researchers think these new fossils alone aren't enough to prove a different type of human existed. Meave Leakey at the Turkana Basin Institute in Nairobi said they "show something completely different ... I feel pretty confident that we're not just dealing with variation in one species."

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