Why are some babies born with hair and other have none?

A friend of mine asked me this question today. I didn't know the scientific answer, so I decide to do some research to educate myself on the proper reason. I visited a few sites and was surprised that there wasn't more information on this topic.  However I did learn a few things in the process.
Babies hair growth patterns are based on genetics, ethnicity, and hormones. Whether your baby is born with a head full of hair or only a few strands, growth pattern change within the first year of birth. It's not uncommon for babies to experience hair loss in the first year. This is due to them spending excessive amounts of time of their backs. Most babies have that infamous bald spot in the back of their head because of the friction from infant bedding, car seats, swings, etc. The hair loss will come to a halt as the child spends more time upright.
When new hair starts to come in (as early as 6 month and as late as late toddler-hood) it will be a different texture, color or both. When the new hair comes in, it's important to care for the hair gently as it is fragile. If you aren't careful you can damage the hair before it has a chance to grow in completely. Barrettes, rubber bands, harsh products, and braids can cause damage to a babies hair. Keep in mind that a babies hair should only be shampooed twice a week and if African American then once a week. You want to preserve whatever amount of natural oils they produce as it is limited.
(Credit: www.parenting.com -Dr. Dan Brennan M.D)
If you are wondering if your baby will grow hair, they will eventually. Every baby is different, hair growth pattern differ on a case by case bases. Doctors say that there is a correlation between heartburn and hair growth. By the fifth month of pregnancy the fetus has started to grow hair and by the last four weeks, hair thickens as he/she prepares for birth. A study was done that showed that women with elevated levels of estrogen had babies with more hair than those with lower levels. Hormones in babies dramatically drops after birth which is also a determinant in loss of hair.
(Credit: www.modernmom.com)
Make sure as a parent you are doing your part to make sure your child is retaining a head of healthy hair even if its minimal.