Q: If we need to feed additional data to the network, do we train it with existing data + new data or we can just train it on a new data? I'm asking because if

Q: If we need to feed additional data to the network, do we train it with existing data + new data or we can just train it on a new data? I'm asking because if we need to train it with both old and new data every time we have something new, that's not similar to human learning.