Editing Human intelligence (section)

=== Investment theory ===
Based on the [[Cattell–Horn–Carroll theory]], the tests of intelligence most often used in the {{clarify|text=relevant|reason=relevant to what?|date=August 2023}} studies include measures of [[Fluid and crystallized intelligence|fluid ability (''g<sub>f</sub>'') and crystallized ability (''g<sub>c</sub>'')]]; that differ in their trajectory of development in people.<ref>{{cite journal | last1 = Horn | first1 = J. L. | last2 = Cattell | first2 = R. B. | year = 1966 | title = Refinement and test of the theory of fluid and crystallized general intelligences | journal = Journal of Educational Psychology | volume = 57 | issue = 5| pages = 253–270 | doi=10.1037/h0023816| pmid = 5918295 }}</ref> The "investment theory" by Cattell<ref>{{cite book|last=Cattell|first=R. B.|year=1987|title=Intelligence: Its structure, growth and action|location=New York|publisher=North-Holland}}</ref> states that the [[individual differences]] observed in the procurement of skills and knowledge (''g<sub>c</sub>'') are partially attributed to the "investment" of ''g<sub>f</sub>'', thus suggesting the involvement of [[fluid intelligence]] in every aspect of the learning process.<ref>{{cite journal | last1 = Kvist | first1 = A. V. | last2 = Gustafsson | first2 = J. E. | year = 2008 | title = The relation between fluid intelligence and the general factor as a function of cultural background: A test of Cattell's investment theory | journal = Intelligence | volume = 36 | issue = 5| pages = 422–436 | doi=10.1016/j.intell.2007.08.004| hdl = 10419/78682 | hdl-access = free }}</ref> The investment theory suggests that personality traits affect "actual" ability, and not scores on an [[IQ]] test.<ref>{{cite book|last=Cattell|first=R. B.|year=1971|title=Abilities: their structure, growth, and action|location=Boston|publisher=Houghton Mifflin}}</ref>

Hebb's theory of intelligence suggested a bifurcation as well, Intelligence A (physiological), that could be seen as a semblance of [[fluid intelligence]] and Intelligence B (experiential), similar to [[crystallized intelligence]].<ref>{{cite journal|last=Hebb|first=D.O.|year=1939|title=Intelligence in man after large removals of cerebral tissue: Report of four frontal lobe cases.|journal= The Journal of General Psychology|volume=21|number=1|pages=73–87|url=https://www.tandfonline.com/doi/abs/10.1080/00221309.1939.9710587|doi=10.1080/00221309.1939.9710587}}</ref>