diff --git a/creatur.cabal b/creatur.cabal
--- a/creatur.cabal
+++ b/creatur.cabal
@@ -1,5 +1,5 @@
 Name:              creatur
-Version:           5.4.2
+Version:           5.5.0
 Stability:         experimental
 Synopsis:          Framework for artificial life experiments.
 Description:       A software framework for automating experiments
@@ -36,7 +36,7 @@
 source-repository this
   type:     git
   location: https://github.com/mhwombat/creatur.git
-  tag:      5.4.2
+  tag:      5.5.0
 
 library
   GHC-Options:      -Wall -fno-warn-orphans
diff --git a/src/ALife/Creatur/Genetics/Recombination.hs b/src/ALife/Creatur/Genetics/Recombination.hs
--- a/src/ALife/Creatur/Genetics/Recombination.hs
+++ b/src/ALife/Creatur/Genetics/Recombination.hs
@@ -68,7 +68,7 @@
 
 -- | Same as @'cutAndSplice'@, except that the two locations are
 --   chosen at random.
-randomCutAndSplice :: (RandomGen g) => ([a], [a]) -> Rand g ([a], [a])
+randomCutAndSplice :: RandomGen g => ([a], [a]) -> Rand g ([a], [a])
 randomCutAndSplice (as, bs) = do
     n <- getRandomR (0,length as - 1)
     m <- getRandomR (0,length bs - 1)
@@ -81,7 +81,7 @@
 
 -- | Same as @'crossover'@, except that the location is chosen at 
 --   random.
-randomCrossover :: (RandomGen g) => ([a], [a]) -> Rand g ([a], [a])
+randomCrossover :: RandomGen g => ([a], [a]) -> Rand g ([a], [a])
 randomCrossover (as, bs) = do
     n <- getRandomR (0,length as - 1)
     return (crossover n (as, bs))
@@ -134,19 +134,19 @@
 
 -- | Randomly select a boolean, but weighted to return True with probability 
 --   p.
-weightedRandomBoolean :: (RandomGen g) => Double -> Rand g Bool
+weightedRandomBoolean :: RandomGen g => Double -> Rand g Bool
 weightedRandomBoolean p = do
   x <- getRandomR (0.0,1.0)
   return (x < p)
 
-randomOneOfPair :: (RandomGen g) => (a, a) -> Rand g a
+randomOneOfPair :: RandomGen g => (a, a) -> Rand g a
 randomOneOfPair pair = do
   chooseFst <- weightedRandomBoolean 0.5
   if chooseFst 
     then return $ fst pair
     else return $ snd pair
 
-randomOneOfList :: (RandomGen g) => [a] -> Rand g a
+randomOneOfList :: RandomGen g => [a] -> Rand g a
 randomOneOfList xs = do
   (_, z) <- randomListSelection xs
   return z
@@ -154,7 +154,7 @@
 ---- | Sample a random element from a weighted list.
 ----   The total weight of all elements must not be 0.
 ---- Adapted from the code in MonadRandom
---randomWeightedChoice :: (RandomGen g) => [(a, Double)] -> Rand g a
+--randomWeightedChoice :: RandomGen g => [(a, Double)] -> Rand g a
 --randomWeightedChoice [] = error "randomFromList called with empty list"
 --randomWeightedChoice [(x,_)] = return x
 --randomWeightedChoice xs = do
@@ -165,7 +165,7 @@
 
 -- | Choose an element at random from a list and return the element and its 
 --   index
-randomListSelection :: (RandomGen g) => [a] -> Rand g (Int, a)
+randomListSelection :: RandomGen g => [a] -> Rand g (Int, a)
 randomListSelection xs = do
   i <- getRandomR (0,length xs - 1)
   return (i, xs !! i)
diff --git a/src/ALife/Creatur/Task.hs b/src/ALife/Creatur/Task.hs
--- a/src/ALife/Creatur/Task.hs
+++ b/src/ALife/Creatur/Task.hs
@@ -90,21 +90,29 @@
 
 runInteractingAgents
   :: (Universe u, Serialize (Agent u))
-    => AgentsProgram u -> Int -> SummaryProgram u -> StateT u IO Bool
-runInteractingAgents agentsProgram minAgents summaryProgram = do
+    => AgentsProgram u -> (Int, Int) -> SummaryProgram u -> StateT u IO Bool
+runInteractingAgents agentsProgram (minAgents, maxAgents) summaryProgram = do
   atEndOfRound summaryProgram
   as <- lineup
-  if length (take minAgents as) < minAgents -- efficient way of checking length, I think
+  let n = length as
+  if n < minAgents
     then do
       writeToLog "Population too small"
       summaryProgram
       writeToLog "Requesting shutdown (population too small)"
       return False
-    else do
-      markDone (head as)
-      -- do that first in case the next line triggers an exception
-      withAgents agentsProgram as
-      return True
+    else
+      if n > maxAgents
+        then do
+          writeToLog "Population too big"
+          summaryProgram
+          writeToLog "Requesting shutdown (population too big)"
+          return False
+        else do
+          markDone (head as)
+          -- do that first in case the next line triggers an exception
+          withAgents agentsProgram as
+          return True
 
 atEndOfRound
   :: Universe u