I have had quite a bit of time lately to just ponder, and one persistent thought has to do with the genealogy I've been doing. In tracking one man and his descendants from 1706, several things have become apparent.
Before the mid-1800's and the time of the Civil War, they bred like rabbits. Almost all of them married, and if a wife died in childbirth, the husband just married a spinster or widowed sister to take care of the brood and perhaps add to it. A family of more than 10-15 children was not uncommon, nor was living a 100 years or more.
After the Civil War, all those numbers changed dramatically. WHY?
We know that before the war, the majority of most household's food was home-grown. If a man grew grain, he took it as needed to a local mill to be stone-ground for bread. If a man didn't grow grain for his family, he probably pitched in with several neighbors in his community for grain. In all cases, they ate whole grains because mass-milling and de-germed grains were not heard of at the time.
They ate locally grown food and humanely-raised chicken, eggs and meat. Fresh, full-bodied milk was available daily, and clean, potable water. Everyone had a garden on land that was teeming with microbial life and had not been over-worked. They knew to let alternate fields lay fallow to replenish the soil.
It was a lot of hard work, and I'm not surprised how easily newly-invented machinery became 'essential'. A team with a wide row of plows could do more work than a man with a single mule and plow. Imagine how much more they could do with machine-drawn equipment!
The local stone mill had a limited capacity, although usually adequate for their community. As men were able to grow larger amounts of grain, the need arose to mass-mill it... then they discovered milled grains soon grew rancid from the exposure of the germ and oils to oxygen. So they de-germed it. I doubt most folks realized the change in nutritional value of de-germed wheat bread, and once bread itself was available from a merchant, I'm sure the over-worked housewife was delighted.
So I believe nutrition was an important factor in the overall decline of longevity. Of course, nutrition is much more than just local availability. The land itself is the contributing factor. As a man could farm more land, he also unintentionally destroyed the viability of that land by removing (within the crops themselves) some essential elements that were not replaced. After all, the tractor didn't produce tons of manure to put back on the fields and it would have been impossible to compost a thousand acres. Chemical fertilizers didn't come along until after WWI when they needed to make money from old munitions factories.
I remember my grandfather, who had been a Kansas county ag agent, talking about growing food in the rich muck of south Florida when he moved his family there about 1920. The muck was so rich that vegetables grew rapidly, to the point of splitting and spoiling in the field. (Muck is the soil made up primarily of humus from drained swampland, easily blown away when dry, and also burns easily.) Fortunately, we no longer destroy as much of our wetlands by draining, for they are a valuable wildlife habitat in the natural cycle of life.
Another thing I notice is after the Civil War, many men married much later in life, and had fewer children. Many men and women did not marry at all, and I doubt availability of a spouse was the big factor. So what was?
Was there a mass PTSD across the land? Or some kind of evolutionary switch that controlled the population rate?
In my research, my solitary ancestor of 1706 had generated over 6,000 people in my database by 1900, 46% of whom bear his surname, and with no more than a generation or two traced who do not bear the name. (i.e. Hardesty women who married into a different surname.) What if all the men had lived, and had offspring at the rate the earlier families did?
The estimated death toll of the Civil War is around 600,000-700,000. More than a million Americans died in WWI, and nearly half a million American servicemen numbered among the 60 million total deaths from WWII.
I am still convinced nutrition was the big factor in the decline of longevity. I just wish I had a better understanding of all the factors in the reproduction rate... not that we need more people to feed, but just that I wonder why?