"No need to change the verbage : `` ... individuals with variations that are fortuitously best suited to changing local environments. `` Like folks who migrated to northern latitudes and happened to have lighter skin ( variation ) were healthier and therefore produced more and healthier offspring . Over generations the lighter skinned came to dominate the group while becomming lighter still . Why is that so difficult ? No one is saying the darker skinned folks never reproduced . They just were n't as successful in the long run ."
"And , the converse is true in the lower latitudes ."
"... individuals with variations that are fortuitously best suited to changing local environments. `` Like folks who migrated to northern latitudes and happened to have lighter skin ( variation ) were healthier and therefore produced more and healthier offspring ."
"And , the converse is true in the lower latitudes ."