Add an odd/even post class to archive pages in Genesis (or WordPress generally) for styling purposes.

functions.php

<?php
// don't copy openting php tag

// Add odd/even classes to blog archives
add_filter ( 'post_class' , 'wsm_oddeven_post_class' );
global $current_class;
$current_class = 'odd';
function wsm_oddeven_post_class ( $classes ) {
   global $current_class;
   $classes[] = $current_class;
   $current_class = ($current_class == 'odd') ? 'even' : 'odd';
   return $classes;
}