diff --git a/rest_framework/serializers.py b/rest_framework/serializers.py
index 21336dc29..a81cbc291 100644
--- a/rest_framework/serializers.py
+++ b/rest_framework/serializers.py
@@ -129,8 +129,8 @@ class BaseSerializer(WritableField):
     _dict_class = SortedDictWithMetadata
 
     def __init__(self, instance=None, data=None, files=None,
-                 context=None, partial=False, many=None, source=None):
-        super(BaseSerializer, self).__init__(source=source)
+                 context=None, partial=False, many=None, **kwargs):
+        super(BaseSerializer, self).__init__(**kwargs)
         self.opts = self._options_class(self.Meta)
         self.parent = None
         self.root = None
@@ -358,9 +358,13 @@ class BaseSerializer(WritableField):
         try:
             value = data[field_name]
         except KeyError:
-            if self.required:
-                raise ValidationError(self.error_messages['required'])
-            return
+            if self.default is not None and not self.partial:
+                # Note: partial updates shouldn't set defaults
+                value = copy.deepcopy(self.default)
+            else:
+                if self.required:
+                    raise ValidationError(self.error_messages['required'])
+                return
 
         # Set the serializer object if it exists
         obj = getattr(self.parent.object, field_name) if self.parent.object else None