Kenyanthropus was created in 2001.

Platyops sterreri was created in 1986.

Because the Great Rift Valley's rapidly eroding highlands have filled the valley with sediments, a favorable environment for the preservation of remains has been created. Australopithecus afarensis, Australopithecus aethiopicus, Australopithecus bosei, Australopithecus anamensis, Kenyanthropus platyops, Ardipithecus ramidus, Ardipithecus kadabba, Homo erectus, Homo ergaster, Homo habilis, Homo sapiens idaltu, and Homo sapiens sapiens have all been found in the rift valley.

No, they just had to make due without things such as modern machinery, electricity, and the internet. They were able to keep themselves alive through harsh conditions, create some new tools, and harness fire. You also have to remember there have been different species of human throughout time. Homo Neanderthalensis, Homo Erectus, Kenyanthropus platyops, Homo sapiens idaltu, and many other species were all very different. They had different physical features as well as different skull structures and brain capacities. To learn how intelligent "cavemen" were, you would have to look into which species you want to learn more about.