Most of us are familiar with the urge to pick up a seashell from the beach or keep a stone from a hiking trip. The object itself may be ordinary, but to the person who keeps it, it serves as a reminder of a particular moment, place or person. Where did this behavior come from? Did early humans do the same? A new study by Tel Aviv University researchers suggests that this practice stretches back approximately half a million years, with important consequences for the evolution of memory.