"Mother Nature" don't know nothin'. Trees are not made to regulate oxygen. Trees were not "made" for anything. They were the result of genetic selection and attrition resulting in an organism that uses sunlight and CO2 to create Glucose, which it then utilizes ("burns") to release energy and, in the process, oxygen and H2O.

The atmosphere is 21% O2 because that's the level where the factors of biological O2 production, biological O2 consumption, chemical recombination, and probably things that I don't understand reach a stable equilibrium. This happens to be just right for the animals living on the Earth's surface because those animals are evolved to use the oxygen present, which is 21%.

We have a nose because some distant ancestor of mankind at the cellular level had a set of proteins designed to detect certain chemicals and other proteins as a survival instinct. As life evolved, a similar concept formed for multicellular organisms. Being able to detect changes in what chemicals are present in the air is a natural survival trait. Also, since the cavity where air is pumped into the lungs is naturally exposed to great quantities of air, it was the natural location for a chemical sensing organ. Hence, a nose.

The reason Intelligent Design believers don't "get" evolutionary theory is because they assume right off the bat that something designed everything. Even when you state that your theory is based on there not being an intelligent designer, they continue to subconsciously assume one (hence the "mother nature" comment).

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An' it harm none, do as ye' will.


Never argue with an idiot. He'll just drag you down to his level of intelligence and beat you with experience.