Why did my brother changed so much when he was born he had blonde hair and grey/blue eyes?

can some one tell me why this extreme change happened

because around the age five or six he all of a suden his hair got dark and his eye turn a medium brown

Why did my brother changed so much when he was born he had blonde hair and grey/blue eyes?

No one know for sure - yet. Scientists now believe that hair and eye color may be controlled by more than one gene and may require more complex genetic modeling to predict. And we are only starting to investigate the impact of environmental factors.

What happened with your brother is not unusual at all. One of my nephews and one of my nieces were born with blue eyes which in both cases turned hazel and then medium brown when they were 5 and 7 respectively, much like your brother.

I'll bet if you ask your parents and grandparents, you will find other people in your family tree with this interesting characteristic. Who knows what color your brother's eyes and hair will be when he is an adult? One of my sisters started out as a baby with red hair and blue eyes - the eyes turned hazel when she was a kid, but then lightened when she became an adult to a very distinct green - and her hair turned brown!

Why did my brother changed so much when he was born he had blonde hair and grey/blue eyes?

The great majority of blonds/blondes do change to brown. It happend to of my siblings. One had big brown eyes that changed to hazel. Who knows? Not me ...but it happens.