What cause gap surrounded by hardwood floors? We live on a military post apartment and when we moved in...

We live on a military post apartment and when we moved in we be told the apartment had be refurshished including the floors. However we have be here a 1 1/2 and there gap in the woodfloor how does this come up and how does one fix it?
Undoing Central Heating Pump Nuts ?
Answers:    EC is right, Shari is not. Do not try to put anything in these gap, trust me. It is humidity causing the wood to expand within summer, and lack of it cause shrinkage in Winter.

A tip, besides the possible use of a humidifier contained by Winter (sort of expensive to run), use a detail vacuum in the hasty Spring to get out as much dirt as you can from the gap, so that when the wood expands, it does not run into blockage.
How long should I keep on to start...
If you are in a cold climate and are using a furnace later the wood drys out and a space will form between the pieces of wood. Your house may be too dry and you require a humidifier in the winter. In the summer the floor will return to middle-of-the-road.