
https://papers.ssrn.com/sol3/Delivery.cfm/SSRN_ID3950757_code410506.pdf?abstractid=3909166&mirid=1

http://www.bertelsmann-stiftung.de/en/topics/aktuelle-meldungen/2017/september/germans-are-more-optimistic-about-their-future-than-their-european-neighbours/

https://theconversation.com/antes-de-humboldt-y-darwin-estuvo-jose-de-acosta-234407