Microblogging site Twitter Inc named Marjorie Scardino, former chief executive of publishing company Pearson, to its board on Thursday following criticism that it lacked diversity in the top ranks of the company. The addition of Scardino, who is also a former CEO of The Economist Group and a former board member of phone maker Nokia, expands Twitter board to eight members. Twitter, which went public last month, was heavily criticized for its all-male board on the eve of its hugely successful public offering. Twitter Chief Executive Dick Costolo had previously publicly brushed off criticism on the lack of diversity and even got into a public debate on Twitter with Stanford University fellow Vivek Wadhwa on the issue.