Thursday, April 28, 2016
I have a book somewhere called Are We Getting Smarter?. It's written by James R Flynn, the man for whom the Flynn effect is named. For those of you who haven't heard of it before, essentially, every decade the average IQ increases. It's estimated that using an IQ test normed in 1997, the average IQ in 1932 would have been 80 (it should be 100).
Flynn's argument is that this change does not reflect actual intelligence. Instead, it reflects changes in testability. Essentially, the increased exposure to tests, due to higher education rates, higher rates of testing in education, and so forth, makes people better at taking tests, and this increases their IQ.
This is certainly possible. But I doubt it accounts for all of the increase. There are a lot of reasons why we should actually be getting smarter, and not just better at taking tests.
First, nutrition. Severe malnutrition in infancy can lower a child's IQ by around 20 points compared to better fed children. In regions where many children are malnourished, a significant correlation between height and IQ is generally found, because both are reduced by malnutrition.
There's an increase in the rates of obesity and obesity-related diseases throughout most developed countries. This is a concern, certainly, but the bright side of this change has been a decline in the rate of severe malnutrition in all age groups, including children. This is also shown by the historical increase in average height in these countries. Further, we've also seen the discovery of vitamins in 1912 and the first vitamin supplements in the 1930s.
In addition, nutritional status for infants and pregnant women has been subject to particular changes. Like all adults, pregnant women have had an increase in overall nutrition. However, they have also been marketed far more nutritional supplements than the general population, and are more likely to take these supplements. Birth control has also improved the health and nutritional status of mothers. Larger families cost more to feed, and repeated pregnancies put more strain on the mother's body - especially if she's also breastfeeding. With birth control, women have more control over their rate of birth, and typically choose to have a small number of children who are well-spaced apart.
And speaking of breastfeeding, the ratio of bottle to breastfeeding has gone through two distinct transitions. Most of us today are taught that 'breast is best', but when formula was first invented, this was not necessarily the case. A malnourished mother will generally produce poorer-quality breastmilk, to the point where if she has access to clean drinking water and enough quality infant formula, her baby could very well be more healthy if formula fed. (In modern times, unfortunately, many malnourished mothers lack access to safe water and/or can't afford to buy enough formula to actually meet their child's needs. If the formula is watered down to make it last, or if the water used to mix the formula contains pathogens, breastfeeding is definitely better regardless of maternal nutritional status. However, due to the lack of birth control in that time period, many mothers from otherwise affluent backgrounds were malnourished purely because of back-to-back pregnancies.)
By the 1970s, however, maternal nutrition had improved substantially. It was around this time that the shift back to breastfeeding began, in part spurred on by evidence that breastfed infants appeared to be doing better than formula fed infants. Soon after, the first studies linking breastfeeding to higher IQ were performed.
Lastly, we've seen the adoption of public vaccination programs. The intended impact, of course, was to reduce the rate of serious complications from viral illnesses, such as congenital rubella syndrome and measles encephalitis (both of which can cause severe cognitive disability). Those complications are rare even when infection rates are high, and therefore would have only a minimal impact on average IQ. But illnesses also interact with malnutrition. Fighting illness takes resources, and a child who is frequently sick will need to eat more when healthy to compensate for the work of fighting off infections. A child who is both malnourished and frequently sick will be in a worse nutritional state than a child with the same diet who has been vaccinated for those illnesses.
So changes in infant and childhood nutrition and health certainly can account for some increase in IQ in the past hundred years. But this isn't the only factor that we've changed.
From ancient times, lead has been used to make many different things, such as pipes for drinking water. The Romans used lead pipes despite at least some awareness of the danger of lead poisoning. Medieval Europeans, on the other hand, seem to have forgotten that there were any dangers to lead, and this continued into the industrial and modern period, when the uses of lead extended from pipes to include paint, gasoline, and other things.
The clinical symptoms of acute lead poisoning are severe and obvious, but such poisoning has always been fairly rare. However, chronic low-level lead exposure in the first five years of life has been shown to lower IQ slightly in children without any clinical symptoms of lead poisoning. Such exposure would have been nearly ubiquitous before we knew the dangers of lead, and has been declining steadily since we removed lead from gasoline and paint and began gradually removing existing lead sources from our lives.
And lead is not the only environmental toxin we have reduced our exposure to, though it's the best documented. While there are probably some new toxins in our environment that we don't yet know the risks of, overall, we have gotten much more careful about what we have in our food, drinking water and the air we breathe - especially for young children. Though we don't know the impact of many of these other toxins on IQ, it's likely that at least some of them can decrease IQ in children.
Lastly, there are also nonbiological environmental effects on IQ. During the first 2 years, the brain is actually pruning unneeded neurons to make room for the ones we will need. And one big determination of whether a neuron makes the cut is how it's being used - for example, a 6 month old baby can distinguish all the possible phonemes in all human language, but by 9 months, babies can only distinguish phonemes that are important in the languages they've heard regularly spoken around them. (For example, a 9 month old exposed to only Japanese will have lost the 'l' and 'r' distinction.)
This becomes particularly crucial when we consider the most disadvantaged children in society. At the beginning of the last century, if a child was orphaned or their parents couldn't care for them, society's answer was to put them in an institutional setting. A child who spends the first few years of life institutionalized will frequently end up with an IQ in the borderline to mild cognitive disability range, as well as suffering a wide range of behavioural and emotional problems. Fortunately, with greater awareness of the impact of orphanages on child development, most developed countries have eliminated or greatly reduced their use - replacing them with foster care, which, while still problematic emotionally, does not have a noticeable effect on the child's IQ score.
But it's not just orphanages that can result in pruning important neurons because of insufficient stimulation. Among children living in family environments, children who are victims of parental neglect typically show a decrease in IQ compared to adequately cared for children. The most dramatic examples are children like Genie, who spent the first 13 years of her life in a single room, chained to a potty chair for most of the time. Although it's uncertain whether Genie's IQ was normal to begin with, her early pre-isolation development was definitely not consistent with the severe cognitive and language impairments she showed in her teens and adulthood.
Of course, cases like Genie are extremely rare, but many more children are exposed to subtle neglect. For example, a parent who regularly leaves her baby to be babysat by a five year old sibling not only places the physical safety of both children at risk - this also results in the baby being exposed to less adult conversation and less competent scaffolding of early interaction and play. Even a parent who is suffering from serious depression tends to interact less with their infant, resulting in poorer language and social skills.
The good news is that exposure to child maltreatment is also decreasing. It used to be that children were not apprehended at all, even for the most severe abuse - only children who were orphaned or willingly relinquished wound up in state care. Since then, more and more children are being removed against their parent's will, including neglected children like the hypothetical five year old babysitter and infant sibling described above.
Even when children are not removed, their care is improving. Psychiatric treatments and parenting skills programs are more readily available and have become more effective. For example, before the invention of antidepressants, the only treatments for depression were hospitalization or expensive psychotherapy, neither of which were as effective. Several decades later, CBT was also invented, and has since become the front-line psychotherapy for depression. Both antidepressants and CBT are as effective in treating depressed parents as they are in treating anyone else, and are certainly reducing the rate of infants exposed to chronic parental depression. Parent-specific programs, such as parental sensitivity training, have also increased tremendously.
In addition, we have also seen an increase in programs aimed specifically at children. Head Start, a program that provides education and support to toddlers and preschoolers from low income families, was first implemented in the 60s. Participation in Head Start appears to improve cognitive ability in children. The same effect may also be seen among low-income children attending preschools in general - and certainly preschool attendance has increased tremendously.