Unless you look at the smallest viable unit.
In particular parasites are minimalist because they aren't complete. They cannot be regarded without their host. All other life is just as interdependent, though not so immediately so.
A human body is made up of a great many separate lifeforms, and some are pretty independent too. The whole cannot survive without all the parts. Where do you want to draw the line to individuate this? A white blood cell probably feels pretty individual. It's all in how you want to look at it.
No living being can survive without the others. Even simple single celled photosynthetic plants cannot survive alone, because they'd eventually drown in their own waste product, oxygen, and at points in the distant past came fairly close. Fortunately, some fungi like item developed into larger and more complex critters called "animals" to sop up some of that oxygen (yes, fungi are genetically considered animals).
So taking the world organism as a whole, since that's the smallest viable unit, it is growing in complexity. Increasing diversity is part of that, as is the development of it's leading edge cells, which we are pleased to presume are ourselves.
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