Where two different things cannot survive without each other.
Ficus macrophylla, commonly known as the Moreton Bay Fig, comes from Australia and has an obligate mutualism with fig wasps.
This means that the figs are only pollinated by fig wasps, and fig wasps can only reproduce in fig flowers.
There were totally failed attempts at growing the plant in Hawaii and California until they introduced the correct wasps.
How can two totally different things just evolve by chance – one cannot survive without the other.
There’s not enough time for trial and error.
I would say that it is by ‘Intelligent Design’ and not chance.