add blood types

Author: jamesmstone

human/blood-types.md

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+# Blood types
+
+I was aware humans have different blood types. `A` `B` `AB` `O` and you can be positive or negative.
+
+However, I was not aware that `A` `B` `AB` `O` are actually groups of blood types. There are actually 45 known human blood types. [See more](https://www.newscientist.com/article/mg26134751-500-a-new-understanding-of-how-your-blood-type-influences-your-health/). But new ones keep getting discovered!
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