Credit goes to AltHype. Siberian Tiger Gestation and Sexual Maturity: https://en.wikipedia.org/wiki/Siberian_tiger#Reproduction_and_life_cycle South China Tiger: https://en.wikipedia.org/wiki/South_China_tiger#Ecology_and_behavior http://www.tigers-world.com/south-china-tiger/ Race differences in Gestation Time: http://sci-hub.cc/10.1093/ije/dyg238 http://sci-hub.cc/10.1016/0306-9877(90)90173-C Race differences in premature births: https://www.cdc.gov/nchs/data/nvsr/nvsr64/nvsr64_09.pdf Race differences in puberty onset: http://pediatrics.aappublications.org/content/110/4/752?download=true https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2876306/ http://www.wschronicle.com/2012/11/black-boys-entering-puberty-earlier-than-counterparts/ Video of Race Differences in Newborn Development: https://www.youtube.com/watch?v=vAAbDzJhoD8 Race differences in infant reactivity: http://pzacad.pitzer.edu/~dmoore/1994_Kagan%20et%20al_Reactivity%20in%20infants_DP.pdf Gestation period and litter size for domestic cats: http://onlinelibrary.wiley.com/doi/10.1111/j.1751-0813.1973.tb06758.x/abstract Gestation periods for horses and ponies: http://sci-hub.cc/10.1016/0301-6226(80)90105-0 Gestation periods and litter side for domestic dogs: http://sci-hub.cc/10.1080/01652176.1993.9694397 Race, Evolution, and Behavior: https://lesacreduprintemps19.files.wordpress.com/2012/11/jp-rushton-race-evolution-behavior-unabridged-1997-edition.pdf Effects of the Hormone Melanin: http://sci-hub.cc/10.1016/j.tree.2008.06.001 The Species Problem: https://en.wikipedia.org/wiki/Species_problem