What makes us unique among primates? Why did we make it while others didn't? It could be our large brain, which gives us the ability to conceptualize and craft sophisticated tools. Perhaps it is the relatively simple, unspecialized hand; our fingers may not be suited for tree climbing, but they do offer a high degree of dexterity (ideal for the manipulation of said sophisticated tools). It may even be as simple as our short broad teeth: while they don't do well on heavy vegetation they are extremely versatile; effective on both meat and plant. While nobody knows the exact answer, we do know that modern humans of genus homo ("man" in latin) arrived on the scene about 2 million years ago and things have never been the same... The different species are (listed in order of their presumed evolution):
Homo Habilis
Habilis ("capable" or "handy") is so named for being the first primate to use shaped bone and chipped stone tools. This is a major advance from the crude sticks and rocks used by the early hominids. First discovered in Tanzania by Leaky (1960), habilis existed about 2 million years ago and is believed to have led the first migration out of Africa and into Asia/Europe. Habilis is the only species of homo to retain an ape-like body and posture, leading some to believe it is a late form of australopithecus. Habilis samples discovered in the mid-1980s have slightly different facial features, causing some anthropologists to name a separate species; homo rudolfensis (see below).
Homo Erectus
The first human ancestor confirmed to walk with an upright posture was named homo erectus, or "upright man". With a large brain and the ability to manipulate sophisticated tools, erectus represents one of the first predominantly modern forms (i.e. few ape features). Originally discovered in Java (1891), erectus lived between 50,000 and 1.6 million years ago. Some African samples are smaller than their European/Asian counterparts and have a more modern face as well. Some consider believe these samples represent homo ergaster; a contemporary of erectus unique to Africa. If this is correct, then modern man could have evolved from either source.
Homo Neanderthalis
Originally described as a slow, sluggish brute, neanderthalis is the basis of many of the "cave man" myths. In reality, the main differences between neanderthalis and modern humans are the cold-climate adaptations which may have ultimately doomed neanderthalis to extinction (in fact, they are so similar that some proposed neanderthalis as a subspecies of homo sapiens). Neanderthalis is intelligent and recent discoveries indicate a primitive spirituality complete with burial ritual. Neanderthalis lived between 30,000 and 200,000 years ago and reasons for its disappearance are the source for considerable debate in the scientific community (i.e. were they genetically obsolete or were they forced out by early humans?). No samples are known in Africa.
Homo Sapiens
Modern humans--us--are classified as homo sapiens, or "wise man". Characterized by a large brain, light skeleton, and simple teeth and hands, Sapiens dates to 130,000 years ago. Some of the oldest fossils are found in South Africa (Border Cave and Klasies River Mouth). One of the remaining mysteries surrounding sapiens is how we got here. Meaning: how did we populate the planet? Some of the competing theories are discussed in the Great Debates section.
Problem Solved?
A 1.8 million year old hominid discovered in Kenya may settle the homo habilis/rudolfensis anomaly. A February, 2003 paper announced that the specimen, originally discovered in 1995, provides evidence that habilis and rudolfensis should be considered a single species. Rutgers University anthropology Professor Robert Blumenschine said the find--a portion of the lower face and upper jaw with intact teeth--shows facial features consistent with both species. This significant find provides an important answer to one of the many mysteries surrounding human ancestry.