I had to chime in on this one!

I have identical, one year old twin girls.  Both exclusively breastfed
until I began solids around 8 months.  Both still nurse often.  The only
dairy they've been exposed to is through me or in baked goods/cooking.
Both eat about the same proportions and have essentially identical
diets.  Carlie's hair lies down and "behaves".  Kendall's hair stands
straight up all over.

Go figure!