The earliest members of the genus Homo are Homo habilis which evolved around million years ago .  Homo habilis has been considered the first species for which there is clear evidence of the use of stone tools . More recently, however, in 2015, stone tools , perhaps predating Homo habilis , have been discovered in northwestern Kenya that have been dated to million years old.  Nonetheless, the brains of Homo habilis were about the same size as that of a chimpanzee, and their main adaptation was bipedalism as an adaptation to terrestrial living. During the next million years a process of encephalization began, and with the arrival of Homo erectus in the fossil record, cranial capacity had doubled. Homo erectus were the first of the hominina to leave Africa, and these species spread through Africa, Asia, and Europe between to million years ago . One population of H. erectus , also sometimes classified as a separate species Homo ergaster , stayed in Africa and evolved into Homo sapiens . It is believed that these species were the first to use fire and complex tools. The earliest transitional fossils between H. ergaster/erectus and archaic humans are from Africa such as Homo rhodesiensis , but seemingly transitional forms are also found at Dmanisi , Georgia . These descendants of African H. erectus spread through Eurasia from ca. 500,000 years ago evolving into H. antecessor , H. heidelbergensis and H. neanderthalensis . The earliest fossils of anatomically modern humans are from the Middle Paleolithic , about 200,000 years ago such as the Omo remains of Ethiopia and the fossils of Herto sometimes classified as Homo sapiens idaltu .  Later fossils of archaic Homo sapiens from Skhul in Israel and Southern Europe begin around 90,000 years ago. 
Fortunately, effective stress-management strategies can diminish the ill effects of stress. The presence of intact, strong, supportive social support networks among friends, family, educational and religious or other group affiliations can help reduce the subjective experience of stress during the teen years. Recognition of the problem and helping teens develop stress-management skills can also be valuable preventive measures. In severe cases, a physician or other health-care professional can recommend counseling or other treatments that can reduce the long-term risks of teen stress.