>The early research in neural networks was hampered by proofs that perceptrons could never solve certain functions, like XOR. DNNs could have been developed muc

>The early research in neural networks was hampered by proofs that perceptrons could never solve certain functions, like XOR. DNNs could have been developed much sooner otherwise. These proofs still hold; pure MLPs (without a modern activation function) aren't very useful, both in theory and practice. What made them useful was the realisation that combining them with a proper activation function makes them much more useful, both theoretically and practically; this discovery took time.