Table 1 Pearson’s r (above the diagonal) and Spearman rho (below the diagonal) between the opportunity for natural selection (Is) and dementia incidence rates  
	All ages		15-49 years old	
	Dementia Incidence	Is	Ageing	GDP PPP	Urban			Dementia Incidence	Is	Ageing	GDP PPP	Urban	
Dementia Incidence	1	-0.827***	0.773***	0.724***	0.518***		Dementia Incidence	1	-0.857***	0.752***	0.793***	0.555***	
Is	-0.830***	1	-0.827***	-0.866***	-0.594***		Is	-0.861***	1	-0.827***	-0.866***	-0.594***	
Ageing	0.776***	-0.835***	1	0.754***	0.560***		Ageing	0.752***	-0.827***	1	0.754***	0.560***	
GDP PPP	0.732***	-0.877***	0.767***	1	0.698***		GDP PPP	0.793***	-0.866***	0.754***	1	0.698***	
Urban	0.522***	-0.647***	0.645***	0.738***	1		Urbanization	0.555***	-0.594***	0.560***	0.698***	1	
Significance level:  * p<0.05, ** p<0.01, *** p<0.001; Sample size range: 175-204
Data sources: Dementia Incidence expressed as the number of new onsets of Alzheimer's disease and other dementias published by Institute for Health Metrics and Evaluation (IHME) in 2020; Reduced natural selection extracted from the previous publication by You et al, https://doi.org/10.1111/eva.12523; Ageing expressed with Life expectancy at 65 years old (2010-2015) published the United Nations; GDP PPP expressed in purchasing power parity in 2015 US dollars published by the World Bank; Urban expressed in percent of population living in urban areas in 2015 published by the World Bank.  
Table 2 Comparison of partial correlation coefficients between dementia incidence rate and each variable when the other three variables were kept statistically constant.  
 
	Dementia incidence rate in population of all ages 	
Variables	r	p		r	p		r	p		r	P	
Is	-0.429	<0.001		-	-		-	-		-	-	
Ageing 	-	-		0.278	<0.001		-	-		-	-	
GDP PPP	-	-		-	-		-0.018	0.800		-	-	
Urban 	-	-		-	-		-	-		<0.05	0.763	
 
Variables	Dementia incidence rate in population 15-49 years old	
	r	p		r	p		r	p		r	P	
Is	-0.452	<0.001		-	-		-	-		-	-	
Ageing*  	NA	NA	 	NA	NA	 	NA	NA	 	NA	NA	
GDP PPP  	-	-		-	-		-0.160	<0.05		-	-	
Urban 	-	-		-	-		-	-		<0.01	0.912	
Significance level:  * p<0.05, ** p<0.01, *** p<0.001; Sample size range: 170 for all analyses 
Data sources: Dementia Incidence expressed as the number of new onsets of Alzheimer's disease and other dementias published by Institute for Health Metrics and Evaluation (IHME) in 2020; Reduced natural selection extracted from the previous publication by You et al, https://doi.org/10.1111/eva.12523; Ageing expressed with Life expectancy at 65 years old (2010-2015) published the United Nations; GDP PPP expressed in purchasing power parity in 2015 US dollars published by the World Bank; Urban expressed in percent of population living in urban areas in 2015 published by the World Bank.  
Table 3 Multiple linear regression analyses to examine predictors of dementia incidence rate
Enter	
Variable	All ages		15-49 years old	
	Beta	Sig.		Beta	Sig.	
Is	-0.620	<0.001		-0.610	<0.001	
Ageing	0.257	<0.001		0.101	0.150	
GDP	-0.010	0.921		0.213	<0.05	
Urban 	0.008	0.891		-0.037	0.504	
Stepwise 	
	All ages			15-49 years old	
Rank	Variable	Adjusted R2		Rank	Variable	Adjusted R2	
1	Is	0.685		1	Is	0.730	
2	Ageing  	0.704		2	GDP PPP	0.738	
Significance level:    p<0.05,   p<0.01,  p<0.001   
Data sources: Dementia Incidence expressed as the number of new onsets of Alzheimer's disease and other dementias published by Institute for Health Metrics and Evaluation (IHME) in 2020; Reduced natural selection extracted from the previous publication by You et al, https://doi.org/10.1111/eva.12523; Ageing expressed with Life expectancy at 65 years old (2010-2015) published the United Nations; GDP PPP expressed in purchasing power parity in 2015 US dollars published by the World Bank; Urban expressed in percent of population living in urban areas in 2015 published by the World Bank.  

Table 4 Correlations between Is and dementia incidence rates in different country groupings
	All ages 		15-49 years old 	
	Pearson's r	Non-parametric		Pearson's r	Non-parametric	
WHO Region						
Africa, n= 46	-0.756***	-0.556***		-0.811***	-0.603***	
Americas, n= 35	-0.759***	-0.721***		-0.769***	-0.736***	
Eastern Mediterranean, n= 21	-0.266	-0.132		-0.638**	-0.639**	
Europe, n= 50	-0.639***	-0.411**		-0.715**	-0.691**	
South East Asia, n= 11	-0.502	-0.373		-0.682*	-0.709*	
West Pacific, n= 27	-0.754***	-0.756***		-0.763***	-0.819***	
The World Bank income 						
High, n= 61	-0.554***	-0.553***		-0.414***	-0.414***	
Upper Middle, n= 53	-0.685***	-0.660***		-0.726***	-0.646***	
Low Middle, n= 48	-0.788***	-0.789***		-0.711***	-0.752***	
Low, n= 28	-0.712***	-0.477**		-0.640***	-0.386*	
The United Nations Gross national income (GNI) 				
High, n= 50	-0.461***	-0.403**		-0.351*	-0.430**	
Upper Middle, n= 49	-0.652***	-0.622***		-0.695***	-0.624***	
Low Middle, n= 44	-0.760***	-0.771***		-0.686***	-0.732***	
Low, n= 31	-0.710***	-0.523**		-0.661***	-0.467**	
Other country groupings 						
ACD, n=30	-0.299	-0.238		-0.609***	-0.638***	
APEC, n=21	-0.724***	-0.681***		-0.532*	-0.486*	
Arab World, n=22	-0.142	-0.026		-0.630**	-0.624**	
English, Official Language, n=49	-0.839***	-0.820***		-0.883***	-0.872***	
LAC, n= 33	-0.749***	-0.665***		-0.768***	-0.694***	
OECD, n=37	-0.602***	-0.327*		-0.409*	-0.404*	
SADC, n=16	-0.770***	-0.629**		-0.933***	-0.779***	
Significance level:  * p<0.05, ** p<0.01, *** p< 0.001;  
Data sources: Dementia Incidence expressed as the number of new onsets of Alzheimer's disease and other dementias published by Institute for Health Metrics and Evaluation (IHME) in 2020; Reduced natural selection expressed as Is which was extracted from the previous publication by You et al, https://doi.org/10.1111/eva.12523. 
Abbreviations: ACD, Asia Cooperation Dialogue; APEC, Asia-Pacific Economic Cooperation; LAC, Latin America & the Caribbean; OECD, Organisation for Economic Co-operation and Development, SADC, Southern African Development Community.