Commenting on Zigzags on a Shell From Java Are the Oldest Human Engravings:

I think we constantly under-estimate the intellectual capacities of the hominids - and over-estimate the level of intelligence needed to produce for example these geometrical forms. We should remember that these were humans and although they would not have been able to construct spaceships, abstract thinking at some level probably was attainable to them. Too often we think that everything that made us human happened during the last stretch to us, instead of incremental development of what now makes us what we are today as species.