diff --git a/GeneticAlgorithm.py b/GeneticAlgorithm.py
new file mode 100644
index 0000000..ffa427f
--- /dev/null
+++ b/GeneticAlgorithm.py
@@ -0,0 +1,112 @@
+import time
+import random
+import math
+
+
+def random_weighted(iterable):
+        '''
+        Random choice of element from iterable
+            with probabilities according to elements values
+        sum(iterable) must be >= 1
+        '''
+        value = random.random()
+        index = 0
+        while value > iterable[index]:
+            value -= iterable[index]
+            index += 1
+        return index
+
+def normalise(iterable):
+    "Return same iterable but decreased so sum is 1"
+    s = sum(iterable)
+    return [(i / s) for i in iterable]
+
+
+class GeneticAlgorithm:
+    '''
+    This class provides interface for adapting and evolving
+    '''
+        
+    def __init__(self,
+                 animal_type=None,
+                 population_size=None,
+                 fitness_function=None,
+                 populations_amount=1):
+        self.animal_type = animal_type
+        self.population_size = population_size
+        self.fitness_function = fitness_function
+        self.populations_amount = populations_amount
+        self.populations = []
+
+    def repopulate(self, i):
+        self.populations[i] = [self.animal_type()
+                               for j in range(self.population_size)]
+
+    def run(self, generations=-1, seconds=10, fitness_bigger=-1,
+                keep_amount=5, keep_fitness=0.01):
+        '''
+        Use this function to start survival:
+        generations - amount of generation for algorithm to calculate;
+                      use -1 to create infinite loop
+        seconds - amount of seconds before shutdown
+                  use -1 to create infinite loop
+        keep_amount - amount of units kept in each generation
+                      if set to -1, keep_fitness is used
+        keep_fitness - threshold of fitness needed to survive
+                      if set to -1, keep_amount is used
+        '''
+        start_time = time.time()
+
+        if len(self.populations) == 0:
+            self.populations = [None] * self.populations_amount
+            for i in range(self.populations_amount):
+                self.repopulate(i)
+        i = 0
+        while i < generations or generations == -1:
+            fitnesses = self.fitness_function(self.populations)
+
+            if time.time() - start_time > seconds and seconds != -1:
+                return [self.populations, fitnesses]
+            else:
+                yield [self.populations, fitnesses]
+
+            for j in range(len(fitnesses)):
+                fitness = [f for f in fitnesses[j]]
+                population = [u for u in self.populations[j]]
+                to_sort = [[a, b] for a, b in zip(fitness, population)]
+                to_sort.sort(key=lambda pair: -pair[0])
+                fitness = [e[0] for e in to_sort]
+                population = [e[1] for e in to_sort]
+
+                if fitness_bigger != -1 and fitness[0] >= fitness_bigger:
+                    return [self.populations, fitnesses]
+            
+                fitness = normalise(fitness)
+                new_fitness = [f for f in fitness]
+                new_population = [u for u in population]
+                if keep_amount != -1:
+                    new_population = new_population[0:keep_amount]
+                    new_fitness = new_fitness[0:keep_amount]
+                else:
+                    if keep_fitness != -1:
+                        while len(new_population) > 0:
+                            if new_fitness[-1] < keep_fitness:
+                                new_fitness.pop()
+                                new_population.pop()
+                    else:
+                        raise Exception("Nor keep_amount neither keep_fitness was set")
+
+                if len(new_population) == 0:
+                    self.repopulate(j)
+                    continue
+                while len(new_population) < self.population_size:
+                    index_1 = random_weighted(fitness)
+                    index_2 = random_weighted(fitness)
+                    u = population[index_1].propagate(population[index_2])
+                    new_population.append(u)
+
+                self.populations[j] = new_population
+                for unit in self.populations[j]:
+                     unit.mutate()
+
+
diff --git a/GeneticAlgorithm_example.py b/GeneticAlgorithm_example.py
new file mode 100644
index 0000000..f667d15
--- /dev/null
+++ b/GeneticAlgorithm_example.py
@@ -0,0 +1,46 @@
+from GeneticAlgorithm import *
+
+
+class SimpleAnimal:
+    "Create random unit"
+    def __init__(self):
+        self.DNA = [random.random() * 10]
+
+    "Return new unit from other 2"
+    def propagate(self, other):
+        new_animal = SimpleAnimal()
+        new_animal.DNA = [(self.DNA[0] + other.DNA[0]) / 2]
+        return new_animal
+
+    "Random mutation, return nothing"
+    def mutate(self):
+        self.DNA[0] += (0.5 - random.random()) ** 3
+
+    def __str__(self):
+        return str(self.DNA)
+
+
+def simple_fitness(populations):
+    '''
+    Return list of lists of non-negative numbers with non-zero sum
+    according to units' fitnesses
+    '''
+    result = [[max(0.00001, 150 - abs(unit.DNA[0] ** 2 + unit.DNA[0] - 15.25))
+                      for unit in population]
+                      for population in populations] # solution to x^2+x-15.25
+    return result
+
+
+GA = GeneticAlgorithm(animal_type=SimpleAnimal,
+                      population_size=3,
+                      fitness_function=simple_fitness,
+                      populations_amount=2)
+for generation in GA.run(seconds=5*60, fitness_bigger=149.8, keep_amount = 2):
+    print("\n\nPop: ", end='')
+    for pop in generation[0]:
+        print("\n     ", end='')
+        for unit in pop:
+            print(unit, end=' ')
+    print("\nFit: ", end='')
+    for fit in generation[1]:
+        print("\n    ", fit, end='')