First, an object of the research is pre-human ancestors' tool use:
> Physical evidence of early hominin perishable tools is scarce. However, it is reasonable to assume the mechanical constraints surrounding tool use and manufacture have remained somewhat constant. Using a functional framework to understand the technical capabilities of extant hominoid tool users presents a novel approach to predict the perishable tool-using capabilities of our earliest relatives.
Note that the Paleolithic, the first period of stone tools, started ~2.58 - 3.3 mya (million years ago); stone can be durable since X mya and we have lots of evidence of that. But our evolutionary line split from the chimps' line ~7 mya (though remember the 7 mya shared ancestor was not a chimpanzee; they evolved too). Before the Paleolithic, and even after it began, our ancestors at times likely used tools made from perishable materials - I cooked dinner with a wooden spoon, myself.
Also, there's the question of culture - something once thought unique to humans:
> Our findings provide insights into the technical skills associated with perishable artefact-making and raise questions about how this knowledge is learnt and culturally transmitted.
There are two ways to pass down traits: genetics, and culture. If you think culture is somehow weaker or secondary, look at the traditions or look at languages that have lasted thousands of years with no genetic basis. An advantage of the cultural method is flexibility - it can be changed today; biological evolution takes awhile.