This has been covered by a lot of news agencies. I got my first look at these ancient human footprints found in Ileret, Kenya from my Economist.com sci/tech feed.
Credit: Brian Richmond/George Washington University
They look human and the research done using detailed measurements of the depressions and swells that are left when a foot presses on soft mud indicates that the creature walked pretty much like we do. Or at least they are very different from the Laetoli footprints found in Tanzania and interpreted to be made by a member of the Australopethicines about 3.75 million years ago. Those footprints suggested a gait that was more ape like. This one seems a more heel to toe style of walking closer to us recent humans. The sediment has been dated to about 1.5 million years old. The footprints indicate a stature and body mass consistent with Homo erectus.
I just wanted to point out something about the tempo of human evolution. In the figure below which shows the changes in cranial capacity seen in the human lineage I have marked the appearance of the modern bipedal gait as suggested by this study to compare the timing of its first appearance with the trend in the evolution of brain size.
Original Source: Nick Matzke
Our modern style of walking appeared well before our brain size reached modern proportions. This shows nicely one of the more important principles of evolution, that different traits within a lineage often evolve at different rates.
The collection of traits - anatomical and behavioral - that define us "modern" humans evolved over a long period of time ... out of step with each other (no pun intended!), the modern style of bipedalism preceding an increase in brain size to the present proportions by more than a million years.
So, there never was any one instance during our evolution when we can say we became modern humans.
When thinking about evolution I don't like the term "modern" humans. It has a teleological feel to it, that somehow evolution was directed towards building us. People use the term to mean that evolution is something that changed our ancestors in the remote past and that once all the pieces of anatomy and behavior feel in place in the Pleistocene, we Holocene "modern" humans haven't changed at all. It's those ancestors of ours who walked funny and could not talk or create art. There is a finality with which we seem to see ourselves.
Now that is simply not true. There is a growing body of evidence most recently compiled in a book by Gregory Cochran and Henry Harpending " The 10,000 Year Explosion" that suggest that the pace of human evolution since the advent of agriculture has in fact quickened.
One million years from now if our species still exists, our descendants will look back to us as an ancient form of human, a population "intermediate" between Homo erectus and themselves - Homo sapien syntheticus? - Evolution has changed us and will continue to do so in ways we cannot entirely predict.
Maybe thinking ourselves as "modern" just reflects our inability to anticipate what we might become in the future.