Hazda Couple and Infant (IMAGE) University of Utah Caption This image shows a Hazda couple and child in northern Tanzania in 1985. University of Utah anthropologist Kristen Hawkes and colleagues' research on Hazda led them to formulate the 'grandmother hypothesis' that grandmothering among early human relatives made the human lifespan evolve so it is much longer than lifespans of other apes. Now, a new study credits grandmothering for the human tendency to form couples or pair bonds. Credit James F. O'Connell, University of Utah Usage Restrictions Credit required License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.