Board Thread:Naruto Discussions/@comment-3279282-20140828133937/@comment-1512913-20140903165714

In my opinion Uzumaki were simply Senju who migrated to land of whirlpools where they mated with red haired people with long life spans, thus Uzumaki came to be. Their DNA is still mostly Senju, hence Ashura's chakra can incarnate into them.