I often see the "myth-busting" fact touted around that the age 25-30 average life expectancy of medieval peasants was brought down by an extremely high infant mortality rate, and that if a medieval peasant made it past their first few years, they could generally expect to live to ages comparable to that of modern people.
Now, I can easily believe that the middle ages have been overly denigrated to make people of the Renaissance and afterwards feel better about themselves, but the above strikes me as over-corrective romanticism.
What I'm really curious about is...where exactly do all these statistics on lifespans and infant mortality rates come from? Exactly *who* was tallying all these dead peasant babies? Where can I look at these records or the analysis thereof?
You're right to be suspicious. More can always be said, especially on your question re where we derive the data from; for the meantime, this previous post by u/alriclofgar addresses the matter of life expectancy.
We don't have registers of births or deaths or the ages computed from them until the 16th century or generally still later, but we do have enough evidence from comparable societies (including early modern Europe) to compile mortality profiles supplemented by the modern census record.
The key factor here is that for any expectation of life at birth, infant (or child, or early adult) mortality in average conditions varies within manageably close bounds: the greater uncertainty is at older ages (often overstated in 19th-century census returns, along with "heaping" at ages ending in -5 or above all -0) and in adjusting for epidemic deaths (which didn't necessarily fall evenly or even consistently on different age groups).
When we arrive at the vital events registration period, English infant mortality ranges from about 150 to 200 per thousand in the 17th-18th centuries when life expectancy averaged 35-40 years (Wrigley &c, English population history from family reconstitution, CUP 1997, p 295-6). Early 19th-century French infants fared rather worse, with a rate of 180-190 against life expectancy of 38-39 (Jean Bourgeois-Pichat, Note sur l'evolution general de la population francaise depuis le XVIII siecle, Population 7:2 ,1952): calculations for the mid-18th century indicate a rate of 280 with life expectancy at 28.
So unless medieval Europe indeed represents a golden age, there's more than enough evidence to indicate infant mortality well in excess of a fifth, and as the period is likelier to resemble 18th-century France than wealthier England it's probable that upwards of a quarter of new-borns didn't reach their first birthday (today's Austria for instance was doing worse than this even into the 1890s).
(This isn't to uphold nonsensical claims for pre-modern longevity: "You could live to be reasonably old if you didn't die first" isn't much use to anybody.)
We don't have registers of births or deaths or the ages computed from them until the 16th century or generally still later, but we do have enough evidence from comparable societies (including early modern Europe) to compile mortality profiles supplemented by the modern census record.
The key factor here is that for any expectation of life at birth, infant (or child, or early adult) mortality in average conditions varies within manageably close bounds: the greater uncertainty is at older ages (often overstated in 19th-century census returns, along with "heaping" at ages ending in -5 or above all -0) and in adjusting for epidemic deaths (which didn't necessarily fall evenly or even consistently on different age groups).
When we arrive at the vital events registration period, English infant mortality ranges from about 150 to 200 per thousand in the 17th-18th centuries when life expectancy averaged 35-40 years (Wrigley &c, English population history from family reconstitution, CUP 1997, p 295-6). Early 19th-century French infants fared rather worse, with a rate of 180-190 against life expectancy of 38-39 (Jean Bourgeois-Pichat, Note sur l'evolution general de la population francaise depuis le XVIII siecle, Population 7:2 ,1952): calculations for the mid-18th century indicate a rate of 280 with life expectancy at 28.
So unless medieval Europe indeed represents a golden age, there's more than enough evidence to indicate infant mortality well in excess of a fifth, and as the period is likelier to resemble 18th-century France than wealthier England it's probable that upwards of a quarter of new-borns didn't reach their first birthday (today's Austria for instance was doing worse than this even into the 1890s).
(This isn't to uphold nonsensical claims for pre-modern longevity: "You could live to be reasonably old if you didn't die first" isn't much use to anybody.)