Combination of the two
Human communities expect individual sacrifices for the greater good, but even individual ants will fight to preserve themselves if it does not conflict with the hive's demands. We just draw the line in different places.
In general, all we can say is that complex structures (cells, organisms, communities, species, maybe even ecosystems?) have an innate tendency to preserve their structure over time, they resist entropy. I bellieve this is a fundamental property of the universe, like the laws of physics.