エラーの解決ができません　：'function' object is not subscriptable

現在、遺伝的アルゴリズムによるワンマックス問題を記述しているのですが、エラーが処理できず困っています。google colabを使って行っています。エラーの原因を教えていただけないでしょうか。
以下が私が書いたコードです。

python3
1#条件設定
2length = 100    #染色体の長さ
3population = 100  #各世代の染色体の数
4new_population = 50  #子孫の数
5mutation_rate = 0.01  #突然変異する確率
6generationcount = 100  #最大世代数
7
8#初期個体群の生成
9import random
10def production(length,population):
11    gene = [[random.randint(0,1) for i in range(length)] for j in range(population)]
12    return gene
13
14#適応度の評価
15def evaluation(gene):
16    evaluate = []
17    for i in range(population):
18        evaluate.append(sum(gene[i])/length)
19    return evaluate
20
21#最小値の探索
22def find_min(evaluate):
23    min = 5
24    for i in range(population):
25        if evaluate[i] < min:
26            min = evaluate[i]
27    return min
28  
29#最大値の探索
30def find_max(evaluation):
31    max = 0
32    for i in range(population):
33      if evaluate[i] > max:
34        max = evaluate[i]
35    return max
36
37#親選択
38def choice(gene):
39    father_index = random.randint(0,99)
40    mother_index = random.randint(0,99)
41    if evaluate[father_index] > evaluate[mother_index]:
42        parent = gene[father_index]
43    else:
44        parent = gene[mother_index]
45    return parent
46
47#交叉
48def crossover(father,mother):
49    offspring = []
50    for i in range(length):
51        p = random.random()
52        if p < 0.5:
53          offspring.append(father[i])
54        else:
55            offspring.append(mother[i])
56    return offspring
57
58#突然変異
59def mutation(gene):
60    for i in range(population):
61        p = random.random()
62        if p < mutation_rate:
63            if offspring[i] == 0:
64                offspring[i] = 1
65            else:
66                offspring[i] = 0
67    return offspring
68
69#エリート主義
70def elite(evaluate,gene,new_gene):
71    sort_evaluate = sorted(evaluate, reverse=True)
72    gene_tmp =[]
73    for i in range(new_population):
74        gene_index = evaluate.index(sort_evaluate[i])
75        gene_tmp.append(gene[gene_index])
76    gene_tmp.append(new_gene)
77    return gene_tmp
78
79#いよいよ繁殖を行っていく
80def main():
81    generationcount = 1
82    gene = production
83    new_gene = []
84
85    while generationcount <= 100:
86        new_gene.clear()
87
88        gene = evaluation(gene)
89        gene = find_min(evaluate)
90        gene = find_max(evaluate)
91
92        print("generation: "+ generationcount)
93        print("MIN: " + min)
94        print("MAX: " + max)
95        if min == 100:
96            break
97
98        for i in range(new_population):
99            father = parents(gene)
100            mother = parents(gene)
101
102            offspring = crossover(father,mother)
103            offspring = mutation(offspring)
104            new_gene.append(offspring)  
105
106        gene = elite(gene,evaluate,new_gene)
107        generationcount += 1
108        print("---------------------------")
109
110if __name__ == "__main__":
111    main()

エラーは以下のようにでました。

error
1<ipython-input-1-5abc9b8df2b6> in evaluation(gene)
2     15     evaluate = []
3     16     for i in range(population):
4---> 17         evaluate.append(sum(gene[i])/length)
5     18     return evaluate
6     19 
7
8TypeError: 'function' object is not subscriptable