Never have Darwin’s observations about survival of the fittest rung more true—especially when it comes to survival in the digital business era. “It is not the strongest of the species that survives,” he wrote, “nor the most intelligent... It is the one that is the most adaptable to change.”

Historically, maintaining a competitive advantage in business was based on having the best product, the lowest prices or the best people. Today, sustainable market leadership is based on an organization’s ability to recognize shifts in the market landscape and adapt quickly. Consequently, digital transformation—the process of becoming a digital enterprise—must be at the top of every IT and business leader’s priority list.

In fact, owing to tectonic shifts in almost every industry the majority of companies—84% to be exact—have digital transformation initiatives already underway. But as these organizations are quickly learning, digital transformation requires more than just a change in business strategy. You need a robust, dynamic IT foundation to facilitate rapid business changes, and a company can only be as agile as its least agile component. Many companies find that the weakest link tends to be the network—particularly the wide area network (WAN), that delivers essential business applications and data across multiple business locations.

One reason for this is that legacy WANs have been in place for the better part of three decades and were originally designed when network devices were manually configured on a box-by-box basis and when traffic traversing the WAN ran from data centers to branch offices. And because application and network teams operated in silos, network changes were often made after all application- and system-level changes were completed.

That model worked up until about five years ago. But legacy WANs can’t respond quickly to modern business demands placed on today’s networks, causing a number of organizations to fall behind their competitors. For example, according to the ZK Research 2017 Network Study the average amount of time required to implement a network-wide change on a traditional WAN network is four months. No digital company will survive at that pace.

“We’re about to enter a world where you don’t need a pile of boxes,” says Kevin O’Toole, SVP of Product Management for Comcast Business. “With software-defined networks, you put in what is essentially a server. You can run software on that server to do all the things those boxes would have to do—and do it a lot cheaper, more reliably and in a way that’s much more manageable.”

That’s where Software-Defined WANs (SD-WANs) come in. By abstracting network control away from the hardware and centralizing it as software, changes can be pushed out across the entire network. Using APIs, an application can fully automate those changes. In this way SD-WAN brings a level of automation, agility and dynamism to the WAN that’s long overdue, especially as WAN traffic is now mission critical and client/server applications have been replaced by cloud computing.

Another important feature of SD-WANs is that they enable low-cost broadband to be used for network transport instead of high-priced private IP services such as Multiprotocol Label Switching (MPLS). The speed of many broadband connections is also significantly faster today than that of a traditional T1 connection (new 1G broadband is, in fact, about 750x faster than a T1). Industries such as retail, hospitality, education, healthcare and manufacturing have been early adopters, but any distributed organization—regardless of vertical—can take advantage of business-grade broadband.

Unlike MPLS, broadband services also offer flexible pricing models, which is similar to cloud pricing. And which means a business could start with a speed of 100 MB and then add more bandwidth—up to 1G when required—so there’s no need to be forced to overprovision the network to leave room for growth.

“MPLS was a wonderful technology 15 years ago,” observes O’Toole. “It was born before the cloud changed everything. SD-WAN allows you to make any network smarter and then grow your network capacity and business capabilities with cost-effective, high-speed bandwidth.” That’s why the combination of SD-WAN and gigabit broadband is bringing about what O’Toole refers to as a transformative, or “next-generational moment.”

In the digital era, speed and agility are everything. Companies that have a dynamic, flexible and agile network to power their business will have the opportunity to leapfrog the competition and maintain a leadership position. Those that refuse to change will struggle to compete and possibly disappear. All of the digital building blocks—such as the Internet of Things, cloud and mobility—are network centric, and the network must evolve to let businesses capitalize on these technologies. That makes the shift to an SD-WAN one of the most critical elements of any organization’s digital transformation plans.

This article originally appeared on Fortune.com.