sorry, It didn't all come?

Question

why does the distance between any two parallels always remain nearly the same, while the distance between any two meridians can vary greatly

Answer 1

I answered your first question but as to why there is a difference between latitude (parallels) and longitude (medidians) it is simple because the first navigators used the north star and measuring its angle with the horizon draws parallel lines. For the longitude or meridian, there is no celestial observation possible because the earth spins around it axis. The only reference is an hour angle defined with an arbitrary reference point which is today Greenwich in England. Accurate longitude measurement was not possible until John Harrison invented the first reliable chronometer in the 18th century. Before that, longitude had to be estimated from dead-reckoning, i.e. measured sailed distance and time.
Because the longitude divide the earth in halves (great-circles) they converge at the poles and are not parallel. The actual distance between the longitudes at any latitude can be easily calculated by multiplying the cosine of that latitude by 60 nautical miles. The latter is the actual definition of the distance between parallels, one minute of latitude being one nautical mile.

Answer 2

mother nature