Humans are Mammals
Humans are descendants of mammals who appeared about 250 million years ago
when the major land masses were connected. Mammals evolved into a great variety
of creatures who had warm bodies, gave birth to live babies and fed them milk.
Mothers assumed a greater role in assuring the survival of babies and social
organization became critical for many mammals to survive. Humans are primates
who, according to genetic analysis, diverged from other placental mammals about
90 million years ago. The oldest known fossil primates are from the Eocene epoch
55 million years ago. Tavaré et al suggested that only 7% of all primate species
that have ever existed are known from fossils. One of the mammalian-primate
lineages, "hominids" are included in the superfamily of all apes, the
Hominoidea. Some hominids became human in a series of transformations that led
to our current form sometime in the last 200,000 years.
Fossil evidence suggests that modern humans are descendants of black Africans who migrated from Africa into Asia and Europe. Ledgard described visiting the real Garden of Eden in Kenya: "An hour’s drive and a 600-metre drop in altitude from Nairobi is Olorgesailie, a Lower Palaeolithic archaeological site on the floor of the Rift Valley in Kenya. It is blisteringly hot. Nothing moves in the heat of the day except dust, gathering into twisters. It might be the closest we have to the Garden of Eden. From the campsite it is possible to make out the outline of the prehistoric lake which once flooded the plain in soapy water. Hominids lived here for 900,000 years. They made handaxes which they used to butcher the hippos, zebras and baboons they hunted and scavenged. The Kenyan anthropologist Louis Leakey uncovered a Homo erectus skull here in the 1940s; the brain cavity was disappointingly small. There must have been grunts, gestures with stones, blood, the sky blotted with vultures, ape children kept back in the darkness. The sense of space here is immense. So too is the sense of known time, hominid time, known at first in the way a beast knows time, in light and darkness, but conscious all the same. The night sky is black lacquered. There are shooting stars. Sometimes there is the sound of hyenas."
Humans are Primates
The tendency in paleoanthropology is to discover more and older fossil
hominids with transitional characteristics. The timing and location of this
transformation will never be known with certainly. Lucy was the first bipedal
Australopithecus Afarensis skeleton found in the mid-1970s with an estimated age
of 3.2 million years. An older, taller hominid skeleton was found in the Rift
Valley, Ethiopia, 2005 just north of Hadar where Lucy was discovered. Nicknamed
'Big Man', the 3.58-million-year-old male skeleton suggested a running and
walking biped nearly 2 metres tall. His scapula which anchors the shoulder
muscles, is similar to that of a modern human suggesting a move from arboreal
life. The oldest Ethiopian hominid, Ardipithecus ramidus (4.4 million years) had
more ape-like arms and feet. In the interim periods other homonids (hominins)
appear and disappear.