Paul Bramscher wrote:

Why?  Intelligent, mammalian and non-mammalian cooperative life on Earth  all developed along social considerations.  Herds, tribes, cities, hives, etc.  Clusters or communities may be better hallmarks (though not exclusive) of intelligence and cooperation than most.

This is probably necessary but certainly not sufficient. Algae forms clusters as do slime molds even to the extent of symbiotic clusters with other molds. But I would not attribute and intelligence to slime mold or algae.