diff --git a/brain.py b/brain.py
index 884f5c6..5cddd03 100644
--- a/brain.py
+++ b/brain.py
@@ -1,17 +1,25 @@
 import numpy as np
+import random
 
+def mat_mult(A,B):
+    return [[sum([A[i][m]*B[m][j] for m in range(len(A[0]))]) for j in range(len(B[0]))] for i in range(len(A))]
 
 class Neural_Network(object):
     # inspired from https://enlight.nyc/projects/neural-network/
-    def __init__(self):
+    def __init__(self, W1=None, W2=None):
         #parameters
         self.inputSize = 3
         self.outputSize = 2
         self.hiddenSize = 3
+        self.fitness = 0 
 
         #weights
-        self.W1 = np.random.randn(self.inputSize, self.hiddenSize) # weights from input to hidden layer
-        self.W2 = np.random.randn(self.hiddenSize, self.outputSize) # weights from hidden to output layer
+        if not W1 :
+            self.W1 = np.random.randn(self.inputSize, self.hiddenSize) # weights from input to hidden layer
+        if not W2 :
+            self.W2 = np.random.randn(self.hiddenSize, self.outputSize) # weights from hidden to output layer
+        # self.w1 = [[random.random() for i in range(self.hiddenSize)] for i in range(self.inputSize)]
+        # self.w2 = [[random.random() for i in range(self.outputSize)] for i in range(self.hiddenSize)]
 
     def predict(self, X):
         #forward propagation through our network
@@ -19,6 +27,10 @@ class Neural_Network(object):
         self.z2 = self.sigmoid(self.z) # activation function
         self.z3 = np.dot(self.z2, self.W2) # dot product of hidden layer (z2) and second set of 3x1 weights
         o = self.sigmoid(self.z3) # final activation function
+        # self.z = mat_mult(X, self.w1) # dot product of X (input) and first set of 3x2 weights
+        # self.z2 = self.sigmoid(self.z) # activation function
+        # self.z3 = mat_mult(self.z2, self.w2) # dot product of hidden layer (z2) and second set of 3x1 weights
+        # o = self.sigmoid(self.z3) # final activation function
         return o
 
     def sigmoid(self, s):
diff --git a/car.py b/car.py
index 3272945..684a51c 100644
--- a/car.py
+++ b/car.py
@@ -2,7 +2,7 @@ import numpy as np
 import pygame
 
 from brain import Neural_Network
-from params import GY, CAR_SIZE, VISION_LENGTH, VISION_SPAN, THROTTLE_POWER, screen
+from params import GY, CAR_MAX_SPEED, CAR_SIZE, CAR_STEERING_FACTOR, VISION_LENGTH, VISION_SPAN, THROTTLE_POWER, screen
 from trigo import angle_to_vector, get_line_feats, segments_intersection, distance
 
 IMG = pygame.image.load("car20.png")#.convert()
@@ -65,6 +65,7 @@ class Car(pygame.sprite.Sprite):
         old_center = self.rect.center
         self.rect.center = (self.speed * vec[0] / 2 + old_center[0], -self.speed * vec[1] / 2 + old_center[1])
         self.update_sensors()
+        self.brain.fitness += int(distance(old_center, self.rect.center))
 
 
     
@@ -81,6 +82,7 @@ class Car(pygame.sprite.Sprite):
                     self.probes[idx] = min(dist, self.probes[idx])
                     if dist < 1.2 * self.speed or self.speed < 0.01 :
                         self.run = False
+                        self.speed = 0
                         print(f'Car {id(self)} crashed')
 
                 # else :
@@ -113,7 +115,7 @@ class Car(pygame.sprite.Sprite):
         )
 
         if self.speed : 
-            self.heading += self.heading_change * 10 / self.speed 
+            self.heading += self.heading_change * CAR_STEERING_FACTOR / self.speed 
             self.heading = self.heading % 360
 
             self.speed += self.throttle #THROTTLE_POWER
@@ -123,7 +125,7 @@ class Car(pygame.sprite.Sprite):
                 # self.speed -= self.throttle #THROTTLE_POWER
 
             self.speed = max(0, self.speed)
-            self.speed = min(self.speed, 7)
+            self.speed = min(self.speed, CAR_MAX_SPEED)
 
         super().update()
 
diff --git a/genetics.py b/genetics.py
new file mode 100644
index 0000000..90b29c5
--- /dev/null
+++ b/genetics.py
@@ -0,0 +1,56 @@
+import numpy as np
+import random
+from brain import Neural_Network
+
+def genetic_selection(brains):
+    # tot_fitness = sum ([int(b.fitness) for b in brains])
+
+    # does not seem very optimized... TBR
+    # constitute a list where every brain is represented
+    # proportionnally to its relative fitness
+    wheel = []
+    for b in brains :
+        wheel += [b] * b.brains
+
+    
+    tot_fitness = len(wheel)
+    half_pop = int(len(brains)/2)
+
+    # selection of pool/2 pair of parents to reproduce  
+    parents_pool = []
+    for _ in range(half_pop):
+        parents_pool.append([round(random.random()*tot_fitness), round(random.random()*tot_fitness)])
+    
+
+def cross_mutate_genes(p1_gene, p2_gene):
+    child = []
+    p1_gene = list(p1_gene)
+    p2_gene = list(p1_gene)
+    for idx,x in enumerate(p2_gene):
+        if random.random() > 0.5 :
+            choice = p1_gene
+        else :
+            choice = p2_gene
+        # Mutation
+        if random.random() < 0.005 :
+            choice[random.randint(0, len(choice - 1))] = random.random()
+            print("Mutation !")
+        child.append(np.array(choice))
+    return child
+
+
+def genetic_reproduction(parents_pool):
+    # every pair of parents will produce a mixed child
+    new_pop = []
+    for [p1,p2] in parents_pool:
+        W1_kid = cross_mutate_genes(p1.W1, p2.W1)
+        W2_kid = cross_mutate_genes(p1.W2, p2.W2)
+        c_brain1 = Neural_Network(W1=W1_kid, W2=W2_kid)
+        c_brain2 = Neural_Network(W1=W1_kid, W2=W2_kid)
+        new_pop.append(c_brain1)
+        new_pop.append(c_brain2)
+    return new_pop
+
+
+
+
diff --git a/main.py b/main.py
index ab10a35..7ffd982 100755
--- a/main.py
+++ b/main.py
@@ -43,6 +43,9 @@ while running_cars :
     pygame.display.flip()
     clock.tick(24)
 
+for c in all_cars :
+    print(f"Car {id(c)} Fitness : {c.brain.fitness})")
+
 while True :
     pygame.display.flip()
     clock.tick(24)
diff --git a/params.py b/params.py
index 0f87ff5..371d197 100644
--- a/params.py
+++ b/params.py
@@ -3,13 +3,16 @@ from pygame.locals import HWSURFACE, DOUBLEBUF
 
 FLAGS =  HWSURFACE | DOUBLEBUF #| FULLSCREEN
 
-GX = 1000
-GY = 1000
-CELL_COLOR = (80,80,80)
-CAR_SIZE=20
-VISION_LENGTH = 50
-VISION_SPAN = 25 # degrees
-THROTTLE_POWER = 3
+GX                      = 1000
+GY                      = 1000
+CELL_COLOR              = (80,80,80)
+CAR_SIZE                = 20
+CAR_MAX_SPEED           = 7
+CAR_STEERING_FACTOR     = 10
+VISION_LENGTH           = 50
+VISION_SPAN             = 25 # degrees
+THROTTLE_POWER          = 3
+
 
 pygame.init()
 screen = pygame.display.set_mode((GX, GY), FLAGS)
diff --git a/trigo.py b/trigo.py
index 67122e4..3821fcb 100644
--- a/trigo.py
+++ b/trigo.py
@@ -17,7 +17,6 @@ def get_line_feats(point1, point2):
     return a,b
 
 
-
 def segments_intersection(line1, line2):
     p1,p2 = line1
     p3,p4 = line2
@@ -42,6 +41,5 @@ def segments_intersection(line1, line2):
         return None # intersect is outside segments
 
 
-
 def distance(point1, point2):
     return math.hypot(point1[0] - point2[0], point1[1] - point2[1])
\ No newline at end of file