Need <? super T> type in Collections.copy

Question

Signature of the Collections.copy method,

public static <T> void copy(List<? super T> dest, List<? extends T> src) 

Just wondering if dest needs to be <? super T> <? super T> , not just <T> ?

 public static void main(String[] args) { simpleCopy(new ArrayList<Number>(), new ArrayList<Number>()); simpleCopy(new ArrayList<Number>(), new ArrayList<Integer>()); } public static <T> void simpleCopy(Collection<T> dest, Collection<? extends T> src) { for (T element : src) dest.add(element); }