Homo sapiens have existed in the form we do today for only about 50,000 years. Go back 2 million years ago though, and there were several kinds of archaic humans. It was near the end of the Australopithecus era (you may have heard of Lucy), and the beginning of the time of Paranthropus and Homo erectus, one of Homo sapiens' direct ancestors. It's easy to assume that one group died off before the next came on the scene, but they overlapped, according to new research.

"We know that the old idea, that when one species occurs another goes extinct and you don't have much overlap, that's just not the case," study coauthor Andy Herries, a paleoanthropologist at La Trobe University in Australia, told Smithsonian magazine.

The recent find, published in the journal Science, comes out of the Drimolen Paleocave System in South Africa. This area is a gold mine of ancient ancestry; over 160 remains have been found there already, and now, the oldest Homo erectus discovery, a cranium, has been found there, dating to about 2 million years ago. Also found were skull fragments and teeth of Paranthropus robustus, and our earlier human ancestor, Australopithecus, who was also known to live in the same area at the same time.

Lucy the australopithecine, Australopithecus afarensis Lucy belonged to the extinct species Australopithecus afarensis, portrayed here in a sculptor's rendering. (Photo: Dave Einsel/Getty Images)

These recently discovered fossils are the oldest examples of their respective species ever discovered.

"Here we have evidence of all three genera, Homo, Paranthropus and Australopithecus, sharing the landscape at just about the same time," David Strait, a paleoanthropologist at Washington University in St. Louis and co-author of the paper, told The New York Times. "It is our first really good look at the time that this replacement is taking place and that’s pretty exciting."

It's well-known that the later human variants (hominins is the term scientists use for modern and related humans) diverged, evolved and then intermixed: Groups of hominins left East Africa and explored North Africa, Europe and Asia. As those early humans moved through various environments, some stayed and adapted to local conditions while others moved on. They might bump into each other again, sometimes using the same places to fish, or shelter. And sometimes they would die there, leaving the fossil record for modern Homo sapiens to find.

"The truth is that from about 2 million years ago until around 10,000 years ago, the world was home, at one and the same time, to several human species. And why not? Today, there are many species of foxes, bears, and pigs. The earth of a hundred millennia ago was walked by at least six different species of man," writes Yuval Harari in his book, "Sapiens: A Brief History of Humankind."

reconstruction of Neanderthal face

A reconstruction of a Neanderthal who lived some 50,000 years ago in what's now Spain, by Italian scientist Fabio Fogliazza. (Photo: Cesar Manso/AFP/Getty Images)

Muscular, bulky Neanderthals were well-suited to the Ice Age climate of western Eurasia, and Homo erectus populated east Asia (and did so successfully for 2 million years). Homo soloensis was found on the Indonesian island of Java, and another tiny island was home to Homo floresiensis; the people there were petite, reaching a maximum height of just 3 1/2 feet due to limited local food resources. The remains of Homo denisova were found in a Siberian cave, but they traveled far and wide; their DNA has been found in modern Australian aborigines, Polynesians, Fijiians and others.

Other humans continued to evolve within Africa, including Homo rudolphenisis and Homo ergaster. And like the others, Homo sapiens (that's us) also came out of Africa, and then met up with many of these species as we moved around the world. And by "met up with," I mean a few things, including sex that resulted in offspring. Just last year, a half-Denisovan, half-Neanderthal child, was found, proving that successful procreation occurred.

And of course, the proof is also in our DNA. As mentioned above, Denisovan DNA is present in some populations and most non-Africans have some Neanderthal DNA. (For example, according to my 23andMe report, I have 249 variants, which is lower than average.)

We Homo sapiens live in a lonely time: Throughout most of human history, there were many other kinds of humans on the planet with us — we are still discovering new ones all the time. So what happened to them all?

There are plenty of theories: "The Interbreeding Theory tells a story of attraction, sex, and mingling," writes Harare. "As the African immigrants spread around the world, they bred with other human populations, and people today are the outcome of this inbreeding."

This idea is at least partially backed up by Denisovan and Neanderthal DNA found in modern humans. But another possibility is that Homo sapiens outcompeted Neanderthals and others, over time starving them of resources. Or we may have killed these other people for being so different from us. As Harare writes, "Tolerance is not a sapiens trademark."

Starre Vartan ( @ecochickie ) covers conscious consumption, health and science as she travels the world exploring new cultures and ideas.

3 different early human ancestors lived at the same time, in the same place
Newly discovered fossilized skulls found in South African cave show Australopithecus, Paranthropus and Homo erectus living together in the same era.