Scientists have discovered some of the oldest stone tools ever found at a research site in Kenya. But the find created a mystery about which group of early humans made and used the tools. A study recently published in Science suggests early humans used the tools to cut up animals for food about 3 million years ago. In the past, scientists thought our direct ancestors were the ones making and using tools. But two teeth from an extinct human-like creature were found at the site. This led researchers to believe that other kinds of hominins might have picked up tools too. The term hominin is still developing and is used to describe species that are considered human or closely linked to humans. The team said the newly found tools are probably the oldest example of what is known as the Oldowan toolkit. This was a set of tools that spread across Africa and beyond during the Stone Age.