diff --git a/src/mw_engine/natural_rules.clj b/src/mw_engine/natural_rules.clj
index b21ce61..06de00c 100644
--- a/src/mw_engine/natural_rules.clj
+++ b/src/mw_engine/natural_rules.clj
@@ -87,13 +87,13 @@
       (cond (> (* (population cell :deer) 10) (get-int cell :fertility))
         (merge cell {:deer (int (/ (get-int cell :fertility) 10))})))
     ;; deer gradually spread through the world by breeding or migrating.
-;;     (fn [cell world]
-;;       (let [n (apply + (map #(population % :deer) (get-neighbours world cell)))]
-;;         (cond (and
-;;                 (= (population cell :deer) 0)
-;;                 (>= n 2))
-;;           (merge cell {:deer (int (/ n 2))}))))
-    ;; deer breed.
+    (fn [cell world]
+      (let [n (apply + (map #(population % :deer) (get-neighbours world cell)))]
+        (cond (and
+                (= (population cell :deer) 0)
+                (>= n 2))
+          (merge cell {:deer (int (/ n 2))}))))
+    deer breed.
     (fn [cell world]
       (cond
         (>= (population cell :deer) 2)
@@ -114,13 +114,13 @@
        (cond (> (population cell :wolves) (population cell :deer))
          (merge cell {:wolves 0})))
     ;; wolves gradually spread through the world by breeding or migrating.
-;;     (fn [cell world]
-;;       (let [n (apply + (map #(population % :wolves) (get-neighbours world cell)))]
-;;         (cond (and
-;;                 (= (population cell :wolves) 0)
-;;                 (>= n 2))
-;;           (merge cell {:wolves 2}))))
-    ;; wolves breed.
+    (fn [cell world]
+      (let [n (apply + (map #(population % :wolves) (get-neighbours world cell)))]
+        (cond (and
+                (= (population cell :wolves) 0)
+                (>= n 2))
+          (merge cell {:wolves 2}))))
+    wolves breed.
     (fn [cell world]
       (cond
         (>= (population cell :wolves) 2)
diff --git a/src/mw_engine/utils.clj b/src/mw_engine/utils.clj
index 86cc016..5b2b7ec 100644
--- a/src/mw_engine/utils.clj
+++ b/src/mw_engine/utils.clj
@@ -48,11 +48,12 @@
 (defn get-neighbours
   ([world x y depth]
     "Get the neighbours to distance depth of the cell at x, y in this world."
-    (map #(get-cell world (first %) (first (rest %)))
-       (remove #(= % (list x y))
-               (combo/cartesian-product
-                 (range (- x depth) (+ x depth))
-                 (range (- y depth) (+ y depth))))))
+    (remove nil?
+            (map #(get-cell world (first %) (first (rest %)))
+               (remove #(= % (list x y))
+                 (combo/cartesian-product
+                   (range (- x depth) (+ x depth 1))
+                   (range (- y depth) (+ y depth 1)))))))
   ([world cell depth]
     "Get the neighbours to distance depth of this cell in this world."
     (get-neighbours world (:x cell) (:y cell) depth))