. How did Mary Leakey’s discovery change the modern understanding of prehistoric humans? The artifacts she discovered offered evidence that early hominids lived in Ethiopia about three million years ago. The remains she dug up at Olduvai Gorge proved Homo erectus were the first to use tools. The bone she found provided evidence that early hominids made tools in East Africa almost 2 million years ago. The skeleton she excavated proved that early hominids walked upright and were almost four feet tall.