Google search is very strict to penalize the duplicate contents of your blog. Wordpress is actually producing duplicate content for search engines without your control.
e.g

You may have same content /post for the following example urls

http://www.example.com/date/post_title
http://www.example.com/date
http://www.example.com/category/post_title
http://www.example.com/tag

when these urls are indexed by the google the search engine find that these all have same content and some time its difficult to find what is the original source of these contents.

Here I am going to share a simple piece of code by inserting these lines into your header.php file you can avoid duplicate content being indexed by the search engine

if((is_home() && ($paged < 2 )) || is_single() || is_page() || is_category()){
echo ‘’;
} else {
echo ‘’;}

copy the above lines and past these into your header.php. For any further suggestions or questions you can put your comments below the post so that I can answer your questions