diff --git a/src/propeller/downsample.cljc b/src/propeller/downsample.cljc
index 8c85ab8..b1e8d02 100644
--- a/src/propeller/downsample.cljc
+++ b/src/propeller/downsample.cljc
@@ -10,7 +10,7 @@
 
 (defn select-downsample-random
   "Selects a downsample from the training cases and returns it"
-  [{:keys [downsample-rate training-data]}]
+  [training-data {:keys [downsample-rate]}]
   (take (int (* downsample-rate (count training-data))) (shuffle training-data)))
 
 (defn update-case-data
diff --git a/src/propeller/gp.cljc b/src/propeller/gp.cljc
index 3c89f00..4af4474 100644
--- a/src/propeller/gp.cljc
+++ b/src/propeller/gp.cljc
@@ -4,6 +4,7 @@
             [propeller.genome :as genome]
             [propeller.simplification :as simplification]
             [propeller.variation :as variation]
+            [propeller.downsample :as downsample]
             [propeller.push.instructions.bool]
             [propeller.push.instructions.character]
             [propeller.push.instructions.code]
@@ -44,12 +45,16 @@
   ;;
   (loop [generation 0
          population (mapper
-                      (fn [_] {:plushy (genome/make-random-plushy instructions max-initial-plushy-size)})
-                      (range population-size))]
-    (let [evaluated-pop (sort-by :total-error
+                     (fn [_] {:plushy (genome/make-random-plushy instructions max-initial-plushy-size)})
+                     (range population-size))
+         indexed-training-data (downsample/assign-indices-to-data argmap)]
+    (let [training-data (if (= (:parent-selection argmap) :ds-lexicase)
+                          (downsample/select-downsample-random indexed-training-data argmap)
+                          indexed-training-data)
+          evaluated-pop (sort-by :total-error
                                  (mapper
-                                   (partial error-function argmap (:training-data argmap))
-                                   population))
+                                  (partial error-function argmap training-data)
+                                  population))
           best-individual (first evaluated-pop)]
       (if (:custom-report argmap)
         ((:custom-report argmap) evaluated-pop generation argmap)
@@ -61,7 +66,7 @@
             (prn {:total-test-error
                   (:total-error (error-function argmap (:testing-data argmap) best-individual))})
             (if (:simplification? argmap)
-              (let [simplified-plushy (simplification/auto-simplify-plushy argmap (:plushy best-individual) (:simplification-steps argmap) error-function (:training-data argmap) (:simplification-k argmap) (:simplification-verbose? argmap))]
+              (let [simplified-plushy (simplification/auto-simplify-plushy argmap (:plushy best-individual) (:simplification-steps argmap) error-function (:testing-data argmap) (:simplification-k argmap) (:simplification-verbose? argmap))]
                 (prn {:total-test-error-simplified (:total-error (error-function argmap (:testing-data argmap) (hash-map :plushy simplified-plushy)))}))))
         ;;
         (>= generation max-generations)
@@ -73,4 +78,5 @@
                                          #(variation/new-individual evaluated-pop argmap))
                              (first evaluated-pop))
                        (repeatedly population-size
-                                   #(variation/new-individual evaluated-pop argmap))))))))
+                                   #(variation/new-individual evaluated-pop argmap)))
+                     (update-case-metadata evaluated-pop))))))
diff --git a/test/propeller/utils_test.cljc b/test/propeller/utils_test.cljc
index 1212e24..30ba7e5 100644
--- a/test/propeller/utils_test.cljc
+++ b/test/propeller/utils_test.cljc
@@ -96,16 +96,16 @@
 (t/deftest select-downsample-random-test
   (t/testing "select-downsample-random"
     (t/testing "should select the correct amount of elements"
-      (t/is (= (count (ds/select-downsample-random {:training-data (range 10) :downsample-rate 0.1})) 1))
-      (t/is (= (count (ds/select-downsample-random {:training-data (range 10) :downsample-rate 0.2})) 2))
-      (t/is (= (count (ds/select-downsample-random {:training-data (range 10) :downsample-rate 0.5})) 5)))
+      (t/is (= (count (ds/select-downsample-random (range 10) {:downsample-rate 0.1})) 1))
+      (t/is (= (count (ds/select-downsample-random (range 10) {:downsample-rate 0.2})) 2))
+      (t/is (= (count (ds/select-downsample-random (range 10) {:downsample-rate 0.5})) 5)))
     (t/testing "should not return duplicate items (when called with set of numbers)"
-      (t/is (= (count (set (ds/select-downsample-random {:training-data (range 10) :downsample-rate 0.1}))) 1))
-      (t/is (= (count (set (ds/select-downsample-random {:training-data (range 10) :downsample-rate 0.2}))) 2))
-      (t/is (= (count (set (ds/select-downsample-random {:training-data (range 10) :downsample-rate 0.5}))) 5)))
+      (t/is (= (count (set (ds/select-downsample-random (range 10) {:downsample-rate 0.1}))) 1))
+      (t/is (= (count (set (ds/select-downsample-random (range 10) {:downsample-rate 0.2}))) 2))
+      (t/is (= (count (set (ds/select-downsample-random (range 10) {:downsample-rate 0.5}))) 5)))
     (t/testing "should round down the number of elements selected if not whole"
-      (t/is (= (count (ds/select-downsample-random {:training-data (range 3) :downsample-rate 0.5})) 1))
-      (t/is (= (count (ds/select-downsample-random {:training-data (range 1) :downsample-rate 0.5})) 0)))
+      (t/is (= (count (ds/select-downsample-random (range 3) {:downsample-rate 0.5})) 1))
+      (t/is (= (count (ds/select-downsample-random (range 1) {:downsample-rate 0.5})) 0)))
     (t/testing "should not return more elements than available"
-      (t/is (= (count (ds/select-downsample-random {:training-data (range 10) :downsample-rate 2})) 10))
-      (t/is (= (count (ds/select-downsample-random {:training-data (range 10) :downsample-rate 1.5})) 10)))))
+      (t/is (= (count (ds/select-downsample-random (range 10) {:downsample-rate 2})) 10))
+      (t/is (= (count (ds/select-downsample-random (range 10) {:downsample-rate 1.5})) 10)))))