Unless your flooring is covered with carpeting, besides the aesthetic problems with gapping you may also notice that the floor feels drafty. This is normal airflow coming up from your basement or crawlspace.
You have two options (though I would not exactly call them "solutions"):
- Patching - Fill in the gaps with wood filler. Force in the filler as far as possible with a putty knife. Sand to the level of the flooring after the filler has hardened. This is not a great option. The surrounding floorboards will shift and eventually start to crack the filler.
- Wood Strips - Use your table saw to rip strips out of spare floorboards you might luckily have laying around. Apply glue to the sides of the strips and gently pound the strips into the gaps with a mallet or hammer. Plane or sand down high spots. Also not a perfect option, but better than the wood fill method.