the Golden Ratio, is present not just in mathematics, but may also be present within your own brain and body (at the atomic or subatomic level), what do you think it means? Is this number evidence of a grand design, a massive freak coincidence or something else?

This is open to interpretation and one may fit the explanation to what they see fit. A possible explanation is that this is a "grand design", in which everything that meets the criteria for existence set by nature is encompassed. If this ratio is satisfied, the product is a good one.

It could mean that there is a grand design, or that the human body as well as everything else that exist is a mathematical construction. The mathematical universe hypothesis states that the universe and all the objects that it contains - including humans, is not just described by mathematics, but is mathematics it and on itself. Therefore, the universe and by extension humans, are just mathematical constructions. This explains why the golden ratio is not only present in the human body at the atomic level, but it is also present in a lot of things in the universe - from black holes to the patterns in the shapes of the leafs and even hurricanes and DNA. Even though is tricky to conclude that the universe is a mathematical construction or that there is grand design, it is mind-blowing thinking about why mathematics describe the universe around us so precisely and why we find the same mathematical constants in so many places in nature.