On this day, the sunlit graveyard belonged to the robins.

The harbingers of new life soared and swooped through the kingdom of death at North Side Cemetery in Butler, drawn more by the freshly mown grass than by the quiet stone markers.

	Anita Dufalla, Post-Gazette illustration Click photo for larger image. Related graphics Life expectancy for U.S. women Life expectancy for famous people.

One of the birds alighted briefly in the patch of green between two stones, the first shaped like a gothic spire, the second like a heart on a pedestal. The spire marker read, "Bertha A. Heck, wife of J.H. Kepple, Aug. 3, 1873-Jan. 4, 1904." In its shadow was the heart marker: "Howard, son of JH, BA Kepple, Jan. 27, 1895-Nov. 21, 1903."

The 30-year-old mother and her 8-year-old son were killed less than two months apart by one of the worst typhoid epidemics ever to hit the Pittsburgh region. Its death toll of 127 became so notorious around the nation that Red Cross founder Clara Barton visited the beleaguered city to offer her support.

About 100 yards away, at the bottom of the cemetery, lies another marker. This one belongs to Reuben McElvain, who died 11 days before young Howard, at the age of "63 years and five months," as his obituary in the Butler Citizen put it. McElvain, a justice of the peace and a Civil War veteran, had been ill for five weeks with "catarrh of the stomach," the newspaper said, so that "the food he ate would not digest and he literally starved to death."

In their mute way, these 101-year-old gravestones tell the story of life expectancy a century ago and how it has changed since then. They reveal facts that may be surprising to some, and they even say something about how long we are likely to live in the 21st century.

The main lesson taught by the clustered deaths of Reuben McElvain and Bertha and Howard Kepple is that the "average life expectancy" we might have thought we understood is actually more complicated than it appears.

That's partly because the term has been mistaught in schools for years.

A standard world history textbook being used today in many classrooms is a case in point. In one chapter of Glencoe/McGraw-Hill's "World History: the Human Experience," dealing with the improvement in living conditions in the United States, the textbook says that "in 1850, the average person lived about 40 years. By 1900 most people could expect to live beyond 50."

Right numbers, wrong phrasing.

In both cases, the textbook is talking about average life expectancy, or more technically, "period life expectancy at birth," which is not the same as "how long the average person lived" -- at least not in common-sense terms.

S. Jay Olshansky, an expert on aging and a public health professor at the University of Illinois at Chicago, said the average life expectancy figure is "often misinterpreted and misused as being the average age of death in any particular era."

But it's actually the average of all life spans for those born in a particular year. So in 1903, when childhood deaths from epidemics like typhoid were still too common, the larger numbers of children who died decreased average life expectancy compared with today.

That's the lesson taught by the grave of young Howard Kepple. His mother's marker tells another part of the story. Even though her death came as part of the same epidemic, it's generally true that women of child-bearing age died more often in that era, too, particularly from infections and other problems during delivery. This, too, tended to pull down average life expectancy.

So, while it's true that adults are living longer today than one or two centuries ago, the number of extra years we get is not as dramatic as the history textbook might make it appear.

And the symbolic proof of that is Reuben McElvain, who died the same year as Howard and Bertha Kepple, but was 63.

In 1900, the average life expectancy at birth was 48 for men and 51 for women. But if you looked at the average life expectancy of people born that year who survived to age 20 and had made it past the dangerous period of childhood, it worked out to 62 for men and 64 for women.

So Reuben McElvain died at just about the typical age of someone who had survived the risks of childhood disease or accident. And Olshansky pointed out that the very term "average" means that many of the men who reached age 20 would survive longer than age 62. A case in point in the same Butler cemetery was a farmer named Samuel Taggart, who also died in late 1903, at the age of 90.

This longer life span for people who make it to adulthood is the reason why statements like the one in the World History textbook can be misleading. When it says that "in 1850, the average person lived about 40 years," it is using the average life span at birth. But even in that year -- a half-century before the Butler typhoid epidemic -- the average life span for a 20-year-old man was 59.

This helps explain why previous eras have so many well-known people who lived to ripe old ages.

Just a smattering of famous names makes the point:

St. Augustine, who lived in the fifth century, died at 75. Despite a life of marauding and pillage, Genghis Khan, who lived in the 12th century, survived to age 63. A century later, the more peaceful Marco Polo lived to age 70, and three centuries later, Michelangelo died at age 88.

And then there is the famous example of two of our founding fathers, Thomas Jefferson and John Adams, both of whom died on July 4, 1826, Jefferson at age 83 and Adams at age 90.

There's a problem with spotlighting such famous personalities, though, Olshansky points out.

"When you're talking about famous people in history, they were famous partly because they were able to live as long and be productive for as long as they did," he said, so they don't constitute an average group.

Specialists who look at average groups -- whole national populations, for instance -- can chart when general life expectancy began to grow, and the results give a whole new meaning to the importance of public health measures.

James Riley, a history professor at Indiana University who wrote the book "Rising Life Expectancy: A Global History," said that life expectancy at birth probably stayed in the range of the upper 20s to the 40s from the 1500s until the late 1700s.

Then, starting in Denmark and spreading into the rest of Scandinavia and Britain, there was an upsurge in average life spans, spurred by a variety of factors.

In Britain, which Riley has studied more closely, food supplies became more stable starting in the late 1700s, maybe because crop storage and distribution were better. Edward Jenner's development of the smallpox vaccine also had a huge impact on cutting childhood deaths.

Rising wealth and education also played key roles, Riley said.

As people acquired more disposable income, they could build bigger houses with toilets, running water and extra rooms, which allowed a sick person to be isolated from others, even before scientists had developed the germ theory of disease.

Widespread education of women in the mid-1800s also had a significant impact, Riley said, because it gave women more knowledge and respect within the household, allowing them to insist that their husbands pay for doctors' visits, or resist having another child, which lowered their risks of childbirth complications and meant the other children had more food and other resources.

But nothing had a bigger effect, Riley said, than the rudimentary beginnings of public sanitation: filtered water, indoor toilets and the revolutionary notion that it was healthful to wash the hands and face once a day and wash the entire body once a month.

Those kinds of measures help explain why Japan had its big upsurge in life expectancy in the 1800s despite lagging behind Europe in wealth and industrial development.

The reason? The Japanese advocated daily bathing and boiling water for tea as part of their culture, and even though neither was done for scientific reasons, those customs greatly decreased the infectious germs people were exposed to in the still rural society.

The sanitation battle would be fought for decades and got a later start in the United States.

At the time Butler was hit with its devastating typhoid epidemic, Western Pennsylvania already had a dismal reputation for the bacterial disease, largely because people used the Allegheny and Monongahela rivers and their tributaries both as sources of drinking water and as giant sewage dumps.

From 1873 to 1907, Pittsburgh had the highest death rate from typhoid fever of the nation's largest cities, said Joel Tarr, a Carnegie Mellon University historian.

While the typical typhoid death rate in northern U.S. cities was 35 per 100,000 residents annually (compared to less than one death per 100,000 today), the rate in Pittsburgh was more than 100 deaths per 100,000 residents. At the same time that Pittsburghers were getting much of their drinking water from the Allegheny River, more than 350,000 people upstream were discharging untreated sewage into it.

Through today's lens, the situation cried out for correction. But many of Pittsburgh's leading citizens thought otherwise near the turn of the last century. Even after voters had approved a bond issue for a drinking water filtration plant in 1899, city Public Works Director Edward Bigelow (for whom Bigelow Boulevard is named) insisted that the city's drinking water did not cause typhoid and anyone who said otherwise would discourage investment in the city.

But the Butler epidemic a few years later spurred a state drinking water law, and when Pittsburgh finally began delivering filtered water in 1907, typhoid rates dropped dramatically, Tarr said.

It took several more decades to convince politicians to approve a broad waste treatment system, so even though typhoid rates dropped, deaths from diarrhea and intestinal infections were still higher than average here through much of the first half of the 1900s.

And it may be surprising to some to know that the Alcosan sewage treatment plan, which seems like such a fixture, did not go into operation until 1959.

All of these trends -- vaccinations, rising wealth and education, public sanitation -- caused the first big leap in life expectancy in the developed world, mainly by reducing the deaths of children and younger women.

The gains in this century have come more at the other end of the spectrum.

"Today," Olshansky said, "people are living far longer with things that used to kill us at much younger ages." Not only have treatments for the two big killers -- heart disease and cancer -- extended patients' lives, but he said "people today can go to a local hospital and have an appendix removed in a matter of 45 minutes, which can be a lifesaving procedure that adds decades to your life and which was not a very easy thing to do years ago."

While Reuben McElvain's death at age 63 a century ago shows that our lives are not incredibly longer today, the gains have still been considerable. Olshansky said that the current life expectancy at birth is about 75 for men and 80 for women. How high will it go? Olshansky is a skeptic when it comes to those who claim that people will routinely live past the age of 100 in just a few more decades. The fact that the average male life span for a 20-year-old has increased only about 14 years since McElvain's day shows that the longer the average person lives, the harder it is to make gains.

In his 2001 book, "The Quest for Immortality: Science at the Frontiers of Aging," Olshansky said that when he was growing up near Detroit, he used to go sled riding on a hill he called the "Demon," which was notable mainly because on the long trudge back up the hill, the last several steps were the hardest because it suddenly became much steeper.

The progress on life expectancy in the United States and other developed nations will be the same, he predicts.

Because we have eliminated most childhood deaths, the only "reservoir" we can tap to extend life is at the older end of the spectrum, and that will be "extremely difficult," he wrote, "because survivors to old age have accumulated a lifetime's worth of damage to genes, cells and tissues -- complex damage that poses a huge challenge to biomedical interventions."

His guess? Our ultimate average life spans at birth may average 82 for men and 88 for women.

Riley, the Indiana historian, also thinks that medical intervention as the principal means for longer life may have peaked. Any gains from now on, he said, may rely on our own habits -- our exercise, diet and other choices.

"I think people should think about where good health comes from. Does it come from doctors or outside caregivers, or things that you do to manage your own health? I think we're at a point of transition now, where 20 years ago we relied a lot on doctors and now we're shifting to a point where we're accepting more personal responsibility for health maintenance."

For those who embrace that responsibility, living 30 years past Reuben McElvain's life span will not be unusual.