Do you think animals can be divided into two biological sexes: female and male? Well, it’s way more complicated that that! 

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Sources:
http://www.isna.org/faq/what_is_intersex
https://ghr.nlm.nih.gov/condition/turner-syndrome
http://turners.nichd.nih.gov/pdf/Gender%20and%20TS.pdf
https://ghr.nlm.nih.gov/condition/klinefelter-syndrome
http://www.nadf.us/adrenal-diseases/congenital-adrenal-hyperplasia-cah/
https://ghr.nlm.nih.gov/condition/5-alpha-reductase-deficiency
https://ghr.nlm.nih.gov/condition/androgen-insensitivity-syndrome#genes
http://www.mayoclinic.org/diseases-conditions/congenital-adrenal-hyperplasia/basics/causes/con-20030910
http://jmammal.oxfordjournals.org/content/69/4/849
http://jhered.oxfordjournals.org/content/92/2/100
http://www.smithsonianmag.com/science-nature/whos-laughing-now-38529396/?no-ist
http://www.sciencedirect.com/science/article/pii/S1095643310000942
http://www.nature.com/news/sex-redefined-1.16943

Image Sources:

https://commons.wikimedia.org/wiki/File:Human_male_karyotpe_high_resolution_-_XY_chromosome_cropped.JPG
https://commons.wikimedia.org/wiki/File:Testosterone.PNG