The announcement that Yahoo (YHOO) selected Marissa Mayer as its new chief is a great signal for Silicon Valley. Marissa joined Google (GOOG) as its 20th employee back in 1999 when it was a fledgling company and had an uncertain future. Historically, few women joined or founded startups and gained the kind of experience that enabled Marissa Mayer and Sheryl Sandberg of Facebook (FB) to rise to their positions of responsibility. Yet, we are now seeing some positive signs. For my entire story please click here!