www.pbs.org/wgbh/evolution/library/06/2/l_062_01.html
www.achievement.org/autodoc/page/may1bio-
www.britannica.com/EBchecked/topic/371097/Ernst-Mayr
www.victorianweb.org/philosophy/spencer/spencer.html
www.brainyquote.com/quotes/authors/h/herbert_spencer.html
www.ucmp.berkeley.edu/history/thuxley.html
www.brainyquote.com/quotes/authors/t/thomas_huxley.html
www.nytimes.com › COLLECTIONS › PALEONTOLOGYplato.stanford.edu/entries/spencer
prelectur.stanford.edu/lecturers/gould/
www.achievement.org/autodoc/page/may1bio-
www.britannica.com/EBchecked/topic/371097/Ernst-Mayr
www.victorianweb.org/philosophy/spencer/spencer.html
www.brainyquote.com/quotes/authors/h/herbert_spencer.html
www.ucmp.berkeley.edu/history/thuxley.html
www.brainyquote.com/quotes/authors/t/thomas_huxley.html
www.nytimes.com › COLLECTIONS › PALEONTOLOGYplato.stanford.edu/entries/spencer
prelectur.stanford.edu/lecturers/gould/