Men and mushrooms

1. In general, evolutionary theory explains why two organisms are alike by postulating a common ancestor. Man and monkeys are more alike than man and mushrooms because the common ancestor of man and monkeys is far more recent than the common ancestor for man and mushrooms. Put another way, the man/mushroom split took place far earlier than the man/monkey split. 

2. Of course, even if you grant evolution, it isn't that simple. There's a distinction between a homology and a homoplasy. Two organisms may be alike, not because they are related to each other, but because they are related to a common environment. Adaptive pressures resulted in convergent evolution.

3. How would a creationist account for the fact that man and monkeys are more alike than man and mushrooms? Take a comparison. Why is a sofa more like a chair than a blender? Why is a rocking chair both like and unlike a beach chair or swivel chair? Why is a Chippendale chair both like and unlike a French Provincial chair?

Well, they are all alike inasmuch as they are all designed for sitting–although some are arguably more decorative than utilitarian. They share a common design because they share a common function. 

But beyond that general function are specific functions, which is why a beach chair is less like a rocking chair than two dining table chairs are like each other. 

In addition, some differences are due to artistic variety. 

Generally speaking, chairs are what they are because the chairbler made them that way. But there can be more specific reasons. In some cases he designs different chairs to serve different functions. In other cases, the motivation is aesthetic rather than functional. He likes variety.

And this is analogous to divine creation. Men and mushrooms are different because God made men to be men rather than mushrooms. Men are more like monkeys because God chose to make a world which exhibits the principle of plenitude. A world with maximal variety. Any two kinds of things will have more in common or less in common in relation to other couplings. 

Now, before someone objects that "God did it!" has no explanatory value, would he also say "the chairbler did it!" has no explanatory value? But if, in fact, the chair is the way it is because that's how the chairbler made it, how does that ascription lack explanatory value? That is the ultimate explanation. 

Now, the general theistic explanation allows for more specific reasons, just as the chairbler may have specific reasons for designing chairs one way or another. 

Fauna and flora exist, not because fauna evolved from flora, but because fauna directly or indirectly depend on flora for their existence (e.g. herbivores, carnivores, oxygenation). In addition, due to symbiosis, some flora depend on fauna (e.g. pollination). Although a natural world without fauna may be possible, that will have fewer varieties of fauna.