为什么像Ruby和Python这样的动态语言不具有Java或C＃等接口的概念？

To my surprise as I am developing more interest towards dynamic languages like Ruby and Python. The claim is that they are 100% object oriented but as I read on several basic concepts like interfaces, method overloading, operator overloading are missing. Is it somehow in-built under the cover or do these languages just not need it? If the latter is true are, they 100% object oriented?To my surprise as I am developing more interest