diff --git a/README b/README
index d29cfe1..7de38c7 100644
--- a/README
+++ b/README
@@ -84,10 +84,14 @@ these commands instead:
 		<rate> between 0 and 1.
 	defense <rate>
 		<rate> between 0 and 1.
-	breeding_key <value>
+	breeding_key1 <value>
+	breeding_key2 <value>
 		<value> is arbitrary integer number; default is 0;
 		breeding succeeds only between individuals with key
 		that is near enough (abs(key1-key2) < kappa).
+		key1 is used as the initiator's key, key2 as the
+		receiver's key. (I.e., use different keys for
+		sexually reproducing species.)
 
 In general, higher rate means higher energy maintenance of the
 appropriate actuators.
diff --git a/agent.cc b/agent.cc
index 277d81a..2b117ce 100644
--- a/agent.cc
+++ b/agent.cc
@@ -106,7 +106,7 @@ agent::breed_dir(int dir_x, int dir_y, std::string info)
 	 * a technical problem with in/out buf locking. */
 	assert(a != this);
 
-	if (abs(a->attr.breeding_key - attr.breeding_key) > world::breeding_kappa)
+	if (abs(attr.breeding_key1 - a->attr.breeding_key2) > world::breeding_kappa)
 		return false;
 
 	chenergy(world::breed_out_cost);
diff --git a/agent.h b/agent.h
index 5a33611..747c8bf 100644
--- a/agent.h
+++ b/agent.h
@@ -36,7 +36,7 @@ public:
 		double move;
 		double attack;
 		double defense;
-		long breeding_key;
+		long breeding_key1, breeding_key2;
 	} attr;
 
 	int energy;
@@ -50,7 +50,7 @@ public:
 		attr.move = 1.0;
 		attr.attack = 0.5;
 		attr.defense = 0.5;
-		attr.breeding_key = 0;
+		attr.breeding_key1 = attr.breeding_key2 = 0;
 		energy = world::newborn_energy;
 		dead = false;
 	};
diff --git a/connection.cc b/connection.cc
index 9df4ac0..64b9403 100644
--- a/connection.cc
+++ b/connection.cc
@@ -131,8 +131,10 @@ connection::actions(class agent *agent)
 			sscanf(line.c_str(), "%lf", &rate);
 			if (rate >= 0 && rate <= 1)
 				agent->attr.defense = rate;
-		} else if (negotiation && !cmd.compare("breeding_key")) {
-			sscanf(line.c_str(), "%ld", &agent->attr.breeding_key);
+		} else if (negotiation && !cmd.compare("breeding_key1")) {
+			sscanf(line.c_str(), "%ld", &agent->attr.breeding_key1);
+		} else if (negotiation && !cmd.compare("breeding_key2")) {
+			sscanf(line.c_str(), "%ld", &agent->attr.breeding_key2);
 
 		} else if (negotiation && !cmd.compare("agent_id")) {
 			int id = -1;