David Guggina, head of supply chain at Walmart, said the evolution of the supply chain dates back 50 years at Walmart when the company first invested in distribution centers. They expanded again when Walmart added grocery sales in 1988. He said as consumers began buying online, the retailer added fulfillment centers, and more recently, the company added market fulfillment centers to increase capacity for online grocery. Supercenters have also become fulfillment centers for online orders closer to the customer, reducing final mile costs of delivery and offering store pickup.