Some researchers have claimed that the average IQ of the Irish used to be really low by West European standards but has recently caught up, and this shows that IQ can be raised by improving social conditions.
Russell Warne recently conducted an analysis of 55 samples of 29k Irish examinees, the IQ data collected in various years from 1916 to 2015. The mean was found to be 98.0. As you see in his graph below, there was at most a slight increase in mean IQ over this period. This pattern contradicts the optimistic nurturist view.
A reality-check approach might offer a nice complement to the IQ data. If mean Irish IQ were, say, 85 a century ago, we should not expect Ireland to have produced many eminent scientists.
I will rely on the inventories of significant scientists, mathematicians, and technologists listed in Charles Murray's Human Accomplishment. I will use Scotland, Denmark, Norway, and Finland as comparisons. They are NW European countries with population sizes roughly similar to that of Ireland, and as far as I know, no one has claimed that those countries used to be low-IQ.
You can see from the lists below that Scotland smokes the other countries with 57 significant figures. Pound for pound, Scotland is an impressive country. Denmark is a distant second with 14 eminent men, but Ireland is a close third with 13 significant figures. Norway has 8, and poor Finland only has one. Impressive country but not for its past scientists.
So Ireland falls to the middle of the pack. No reason here to think that the Irish used to be dumb but have only recently improved their intelligence level.
Scotland -- 57 Significant Figures
Astronomy
Thomas Henderson
Biology
Robert Brown
John Haldane
John McCleod
Chemistry
Archibald Couper
John Cranston
William Cullen
James Dewar
Alexander Fleck
Thomas Graham
Charles Macintosh
William Ramsay
Daniel Rutherford
James Swinburne
James Waterston
James Young
Earth Sciences
James Ewing
James Hall
James Hutton
Charles Lyell
William Maclure
Roderick Murchison
William Nicol
Charles Thomson
Physics
David Brewster
James Maxwell
William Thomson
Charles Wilson
Math
James Gregory
Colin Maclaurin
John Napier
James Stirling
Joseph Wedderburn
Medicine
Charles Bell
Alexander Fleming
John Hunter
James Lind
Patrick Manson
Edward Mellanby
John Pringle
James Simpson
Robert Whytt
Technology
John Baird
Alexander Ball
Patrick Bell
James Dewar
Kirkpatrick Macmillan
John McAdams
Andrew Meikle
William Murdock
James Nasmyth
William Rankine
James Thomson
William Thomson
Robert Watson-Watt
James Watt
James Young
Denmark -- 14 Significant Figures
Astronomy
Tycho Brahe
John Dryer
Ejnar Hertzsprung
Ole Romer
Biology
Peter Dam
Johan Fabricius
Hans Gram
Wilhelm Johannsen
Chemistry
Soren Sorensen
Earth Sciences
0
Physics
Erasmus Batholin
Niels Bohr
Hans Orsted
Math
0
Medicine
Niels Finsen
Technology
Valdemar Poulsen
Norway -- 8 Significant Figures
Astronomy
0
Biology
0
Chemistry
Cato Guldberg
Earth Sciences
Jakob Bjerknes
Vilhelm Bjerknes
Peter Waage
Physics
0
Math
Niels Abel
Marius Lie
Caspar Wess
Medicine
Johannes Fibiger
Technology
0
Finland -- 1 Significant Figure
Astronomy
0
Biology
0
Chemistry
0
Earth Sciences
Johan Gadolin
Physics
0
Math
0
Medicine
0
Technology
0
Ireland -- 13 Significant Figures
Astronomy
William Parsons
Biology
John Tyndall
Chemistry
Thomas Andrews
John Bernal
Adair Crawford
Earth Sciences
Francis Beaufort
Edward Sabine
Physics
George Fitzgerald
George Stokes
George Stoney
Ernest Walton
Math
0
Medicine
0
Technology
Arthur Kennedy
Charles Parsons