Based on dimensional analysis and order of magnitude estimation one can understand why for example no warm blooded animal of small size such as rats can live in the north pole, only big animals like bears can. This is because the heat loss (which goes like the surface area of the animal) per mass (which goes like volume, assuming animals have same density) goes like 1/L. Hence heat loss per mass for small sized animal is so high.
Another example is that, warm blooded animals have body temperature on average that does not exceed 40 (I can understand this as an order of magnitude in the following way, this temperature is close to the average environmental temperature on earth which itself is set by radiation received from the sun..etc)
In a similar manner I am trying to understand the following numbers
the length of pregnancy of humans is about 10 months (why not 1 month or 100 months?)
humans live up to 100 years (why not 1 or 10 or 1000 years?)
human eye is sensitive only to the visible band of the EM spectrum