There were 4 children, and one died. I have often wondered why the world's homo sapien population did not grow faster during the period 200,000 BC to 10,000 BC. In his book Extinct Humans, Ian Tattersall has argued that fully modern homo sapiens took shape around 200,000 BC and left Africa around 150,000 BC. http://www.amazon.com/Extinct-Humans-Ian-Tattersall/dp/08133...
The growth of the population was very slow. Someone suggested that at their peak there were 100 million bison worldwide, but it seems to have taken most of human history to catch up with the bison -- we seem to have hit that number only when we began agriculture. As late as the year 1300, the historian Fernand Braudel estimates a world wide population of only 500 million people. We became one of the most successful species in the history of the planet, so why wasn't there faster growth, for such a long time?
That question interests me, so it also interests me that a family, living alone, with fanatic Christian fundamentalist beliefs and no access to contraceptives, still only ends up having 3 surviving children -- not a whole lot in excess of the replacement rate.
Something similar to this must have been going on for many thousands of years.
Long gestation, long time to sexual maturity, prevalence of single births (twins occur naturally in about 1 of 60 births, triplets 1:8100), very high infant mortality (up to 50% or more, much of the increase in human lifespan is actually a decrease in mortality from 0-10 years). Childbirth was highly risky, and many women had large numbers of pregnancies (10 or more weren't uncommon), with a high risk of death in any. Few women lived to old age (an inversion of today's lifespan trends).
Add in subsistence existence with poor food storage and little means to store surplus, and life was tenuous. Civilization and the formation of cities helped get around the food store problem, but introduced disease, particularly with poor management of human wastes and garbage.
Improving available food, energy, sanitation, acute medical care, obstetrics, decreased criminal and military violence, all contributed to an explosion of population beginning in the 19th century, and rapidly accelerating through the 20th.
The article doesn't mention the age of the mother when the family went into isolation in 1936, but judging from the age of the father and the age of the oldest child, she would have been somewhere between her mid/late 20s and late 30s. That could be one reason why she only had two kids in isolation. Also, the family experienced famine, which affects fertility negatively.
And the family lived in one room. The lack of privacy may not have been conducive to reproduction.
They were also at times barely surviving. They might not have had much interest in sex. Even if they did, the mother's reproductive processes may have been reduced due to lack energy/nutrition. You also don't know how many stillbirths they had. It's probably not something they would readily talk about, (and not something that the geologists were eager to discuss).
I assume by fanatic Christian fundamentalist you are thinking this family is similar to David Koresh or perhaps a celebrity TV family such as The Duggers. Her sect, first of all, is an offshoot of the Russian Orthodox Church, not American protestantism. Church-attending Orthodox (as opposed to casual members) would be more likely to have children than this sect. It has more in common with Tolstoyism and its nearest equivalent in the US would probably be Adventism or perhaps Unitarianism in the sense that its adherents are very serious, but they are theologically liberal and opposed to growing the church through baptism and assuming that baptized infants are Christians. So, they were not especially motivated to have children despite being very serious about their religion.
I'm not sure what would be the South American equivalent. I'd look into mystic schismatics that pulled away from the Catholic Church in the 19th century to start. Unless you are using fundamentalist to mean the early 20th century movement specifically, it's misapplied here.
Also, don't forget that agriculture only arose recently, in the grand scale of things - somewhere around 20,000 years ago, and these folks had agriculture - in fact, their suffering is largely based around the fact that they're attempting agriculture in isolation, which doesn't really work with a "tribe" of their scale. You have to have trade, as, as we saw with them, if you lose your seed stock (carrots, almost rye), you're up the proverbial creek. It took second generation wilderness upbringing for what sounds like a instinctive hunting technique - i.e. chase the animal for days until it falls over exhausted, and kill it - this is how some Sub-Saharan cultures have hunted (and may in fact still) for millenia - Khoi, for instance, and is likely actually how humans have hunted since we descended onto the plains. We have no claws or fangs, just a physiology perfectly adapted for running long, long distances. I digress.
Another factor is that crops have changed vastly since the start of agriculture, which is also a major factor in the relative growth rate of human population (along with disease, which arose hand in hand with agriculture, of course) - see Teosinte vs. Corn, and Emmer Wheat vs. Durum. Same plants, shaped by man's hand since time immemorial by selective breeding.
So, yeah. These guys actually had it really well off compared to historic humans, as they had agriculture, but it doesn't function well in isolation, particularly in such a harsh environment as the taiga - don't forget the place used to be inundated with hunter-gatherers before everyone migrated for the cushy disease and war-ridden life agriculture offers.
Survival was a bitch until we figured out farming and trade - and it's improved over the last 150 years or so due to modern medicine (lower infant and adult mortality), improved crops (green revolution), improved productivity (industrial revolution), and all the rest.