Yes, there are several independent lines of evidence. Of course, the evidence is not absolute because we have no means of time travel. But so far as I can find out, there are few, if any, scientists who doubt that our species were hunter/gatherers and egalitarian -- even (as some of the foremost folks in the field have described it) "
fiercely egalitarian".
Perhaps the "biggest" line of evidence are the studies done on the earth's last remaining hunting/gathering groups. Peter Gray -- although he is not a scientist working in the field --
sums up the findings better than most people I've read do:
Of course, the reasoning here is that contemporary hunting/gathering groups closely resemble the hunting/gathering groups of the past and distant past. So far as I can see, there's no substantial reason to doubt that beyond the simplistic claim "We just don't know for sure."
Another line of evidence is based on grave goods. The reasoning goes that, if hunting/gathering societies of the past had routinely been stratified, then we might see large differences in the quantity and quality of grave goods that people were buried with -- just like we find in some known stratified societies, such as ancient Egypt or the Albania of the 1980s. In fact, we have one or two instances (from Russia) where that is the case. In one instance, an individual was buried with such a huge number of beads that it probably took 30,000 man-hours to manufacture all of them! But that guy is by all accounts an outlier. It's almost always the case there's not much difference in grave goods between one ancient hunter/gatherer grave and another.
There are some other lines of evidence, but I think you must get the picture by now.