Final answer:
Homo habilis was the first species to experience a major increase in brain size and use stone tools known as Oldowan tools.
Step-by-step explanation:
The first major increase in brain size and the first use of stone tool technology can be attributed to the species Homo habilis, which existed around 2.5 million years ago.
Homo habilis had a brain volume larger than that of a chimpanzee and used stone tools known as Oldowan tools. These tools were created by smashing smooth rocks together to create sharpened edges and were used for a variety of tasks such as killing animals, butchering meat, and accessing marrow.