Gaps in wood floor

[stevedam850]

We have several areas in our house where our wood floors are getting small gaps between the slats. It’s not just 1 area but all over the 1st floor. The picture below is what one of the gaps look like. Does anybody know what is causing this and how to repair/prevent it from happening again?

Thanks

 

[bud16415]

Mine gap like that every winter and close back up in the summer. Cause is humidity.

Also the reason tongue and groove are just nailed on one side.

 

[oldognewtrick]

How old is the floor? Is this something that just occurred? Any changes in the house, a/c..humidifer...etc?