The life cycle of humans, and indeed of most living creatures on Earth, is easy to understand. We’re born. We go through tremendous growth spurts in which our bodies command lots of resources until we reach maturity. Our need for resources peaks and then falls somewhat as we approach and pass middle age. As we grow even older, we need to make more tweaks to remain as fit as we can be.

Everyone comprehends this. Why don’t we understand -- and employ -- a similar mindset for cities and metro areas?

I was thinking about the life cycle of cities as I read the latest Census updates on metro area growth, released in April. The new 2018 data showed that the metro area population for New York, Los Angeles and Chicago each declined from 2017. New York and L.A.’s population numbers shrank by 0.1 percent; Chicago’s fell by 0.2 percent. The nation’s three largest metros were the only ones in the top 10 to show a year-over-year population decline.

As with so many things, this news requires context. I looked at the population counts for the nation’s 53 largest metros, all of the ones with a population greater than 1 million. From 2017 to 2018, 12 metro areas did indeed lose population, including the big three. The places that saw the biggest drops were Rochester and Buffalo in New York; New Orleans; Pittsburgh; and Hartford, Conn.

But many other places -- mostly in the West and the Sun Belt -- added people over the same period. Phoenix; Orlando, Fla.; Austin; Raleigh, N.C.; and Jacksonville, Fla., led the way, with year-over-year gains of 2 percent or more. On the whole, the 53 largest metros increased their population by 0.7 percent. So the population drop of the three largest metros may be more anomaly than trend.

Further context, found by looking at population changes since 2010, gives us a better sense of trends. Between 2010 and 2018, 49 of the largest 53 metro areas -- including New York, Los Angeles and Chicago -- actually showed population increases. Over those eight years, it was Austin, Orlando, Raleigh, Houston and Dallas that led in population gains. Meanwhile the only decliners were Buffalo, Hartford, Rochester, Cleveland and Pittsburgh, each of which lost about 0.01 to 0.02 percent of their population every year.

All of which brings us back to my life cycle analogy. A case can be made that “younger” metros, or those that have experienced their greatest growth periods since, say, 1970, are similar to teens or young adults. They are are still quite dependent on outside resources to facilitate continued growth. These younger cities still rely heavily on domestic in-migration to grow their regional economies.

“Older” cities, on the other hand -- those whose growth spurts came before 1970 -- are less reliant on domestic net-migration to fuel growth. Young people may cycle in to go to college or start their careers, but that influx is often offset by middle-aged residents who cycle out in search of more affordable housing, better schools and more abundant mid-career job opportunities.

Comparing the growth profile of large, older metro areas with younger and smaller cities makes as much sense as comparing the growth of a 54-year-old adult with that of a 13-year-old teenager. Chicago is not the same as Orlando. Younger metros are still dependent on outside resources for growth; older ones must focus on making good, strategic choices to improve overall efficiency for the years to come.