diff --git a/grow/definition.go b/grow/definition.go
index 7ac8974..fefca6f 100644
--- a/grow/definition.go
+++ b/grow/definition.go
@@ -1,6 +1,7 @@
 package grow
 
 import "io"
+import "math/rand"
 import "sort"
 
 import "gopkg.in/yaml.v2"
@@ -15,6 +16,8 @@ type Definition struct {
 	InstructionsPerFunctionMean   uint64 `yaml:"instructions_per_function_mean"`
 	InstructionsPerFunctionStdDev uint64 `yaml:"instructions_per_function_std_dev"`
 
+	ReturnToBestPeriodMean uint64 `yaml:"return_to_best_period_mean"`
+
 	Samples []*Sample `yaml:"samples"`
 
 	// Sample indices ranked by each output dimension
@@ -67,6 +70,10 @@ func (def *Definition) Grow(statusChan chan<- Status) (*vm.Program, error) {
 	for {
 		status.Attempts++
 
+		if def.ReturnToBestPeriodMean != 0 && rand.Uint64()%def.ReturnToBestPeriodMean == 0 {
+			prog = status.BestProgram.Copy()
+		}
+
 		Mutate(def, prog)
 
 		scores, err := def.score(prog)
diff --git a/grow/defs/pythag.yaml b/grow/defs/pythag.yaml
index 079f469..5b211fa 100644
--- a/grow/defs/pythag.yaml
+++ b/grow/defs/pythag.yaml
@@ -5,6 +5,8 @@ instruction_limit: 10
 instructions_per_function_mean: 5
 instructions_per_function_std_dev: 3
 
+return_to_best_period_mean: 10000
+
 samples:
 - in:  [3,4]
   out: [5]