I have been surprised at the combination of hostility and lack of interest in the intelligence community, regarding the discovery that reaction times have apparently slowed substantially over the past 150 years in England; and the implication that this represents a substantial decline in intelligence - amounting to roughly one standard deviation, or 15 IQ points, or the idea that the average intelligence of about 150 years ago would now in in the top 15 percent of modern intelligence.
Having lived with this knowledge for two years:
I am still fascinated by it, and have find nothing to refute it - on the contrary Michael A Woodley and I have confirmed it (paper submitted) using a completely different method of analyzing reaction time data from a totally independent sample.
But I think I understand better why this information will be resisted - and that is it destructiveness of a great deal of existing research in the field.
A suitable analogy is with Gregory Clarke's book A Farewell to Alms: a brief economic history of the world, which describes the effect of human psychological evolution in the economic history of England. He attributes the industrial revolution primarily to changes in the heritable psychology of the English (implicitly, some combination of increased-intelligence and a more-conscientious and less-aggressive personality).
This brilliant work was generally attacked, or faintly praised then ignored - because if acknowledged by the economics community, FtA would at a stroke destroy almost all previous work done on economic comparisons between nations and over long periods of time that have assumed that humans were essentially inter-changeable.
In a nutshell, Clark's work convincingly destroys much of economics as a discipline, by destroying one of its key assumptions - little surprise, therefore, that economists weren't keen on it, that they sensed a problem...
Similarly, if it is true that human intelligence in countries like England has been declining as rapidly as one IQ point per decade (approximately, on average - and surely varying in speed and magnitude between countries and sub-groups) then this has truly enormous implications in relation to understanding a wide range of phenomena. It throws into doubt all sorts of things.
For example, the striking decline of creative genius (and therefore of scientific and technological innovation) in the West over the twentieth may be explicable substantially on this basis. There are declines in educational attainment. There is the inexorable slump in economic efficiency. All sorts of indirectly-related phenomena such as the rise of bureaucracy and the corruption of democracy may be implicated.
A substantial decline in intelligence is also a direct strike against our covert secular religion of progress - if it is known that each generation is significantly less smart than the preceding one, it becomes harder to believe that they are intrinsically superior and entitled to discarded the wisdom of the ages and remake the world on a new set of principles.
Instead, it looks more like succeeding generation are just too dumb to understand what they have inherited, the culture and the capabilities; and because they fail to understand it - therefore they have no compunction about destroying it.
Instead of the vast scale and complexity of modern society being a product of our greater capability; it becomes revealed as merely an out-of-control artefact of incompetence and corruption - and the inevitable prelude to collapse.
Instead of living in a world where we assume that although we may not personally understand x,y and z - 'the experts' understand it. But these experts are getting dumber by the decade, so pretty soon nobody understands x,y, and z.
The implications of declining intelligence fan-out like the expanding circles from a rock dropped into a pond - even if we are, as yet, unsure of its causes.
One cause is almost surely differential reproductive success among people of differential intelligence - but this only seems to account for about half of the decline - the other cause/s are unknown, although I suspect that an accumulation of deleterious mutations in the gene pool (due to the relaxation of natural selection from child mortality) is likely to be a factor.
But if these are indeed the causes, then looking globally at the unprecedented speed and direction of demographic transformation - and a world where natural selection is now for pure fertility - the decline in global intelligence is certain to be accelerating; and the unprecedented scale of international population migration ensured that this more-rapid intelligence decline will accelerate the already-rapid decline in most native Western populations.
To summarize - we now know, from reaction time slowing, that intelligence has been declining rapidly in England for about 150 years - at very approximately one IQ point a decade; and we know that due to the vast differential in fertility internationally - with rapidly growing and ever younger world population complemented by rapidly ageing and declining Western populations - that the decline in global intelligence must be of a broadly similar (or greater) order of magnitude.
(In reality, these speculative rates of decline will vary both over time and between populations - but numbers are needed, however approximate, in order to handle the consequences over reiterations of the cycle.)
So, a country like England, has been
1. undergoing a decline in intelligence among the native population measured at about 1 IQ point a decade.
There is also:
2. a significant decline in intelligence due to the ageing population
And on top of this there is:
3. ongoing population replacement, at an accelerating rate, due to mass migration. The effect on average intelligence is hard to quantify, but - given differentials in age and fertility of native and migrant populations - could easily be the same as the decline in the native population..
What would this mean?
Well, if the combination of factors led to a decline of 2 IQ points per decade, the consequences would be substantial over a generational time-scale (declining at five IQ points, or one third of a standard deviation per generation) - with an underlying tidal subsidence of capability, an ebbing of innovation, a steady erosion of all activities depending on intelligence (science, technology, arts, the economy, the military, education and so on) - yet invisible to day-by-day, year-by-year inspection.
Over a lifetime of 75 years, there would be a slump of a whole standard deviation of intelligence - which would mean there would be very little overlap between average 'future-modern' intelligence and that of 150 years ago.
So, in about another three generations (75 years) almost all-Victorian English would have been more intelligent than almost all future-modern English-dwelling people will be (with us, now, about half-way between) - since Victorian English were 1SD more intelligent than us, and we now would be 1SD more intelligent than future modern English-dwellers...
Which implies only a tiny, few, percent, overlap in intelligence between the populations of England in Victorian and future-modern times. They would be regarded as essentially distinct populations in terms of intelligence. In 75 years time!
(This is comparable to the largest recently measured intelligence difference between human populations, and very large differences in autonomous cultural capability - the difference-between being able to administer modern technical societies (although probably not to originate them, since our intelligence has already declined) and the remnant of hunter-gatherers/ simple agrarians. )
The man in the street would never notice or understand what was going-on - and would no doubt find 1001 other and more obvious things to blame for the collapse of complexly differentiated modern culture - but he would nonetheless be missing the underlying inexorable reason behind a huge range of linked societal changes.