1
00:00:00,000 --> 00:00:14,000
(背景音乐)

2
00:00:14,000 --> 00:00:17,000
演化五要素的手指譬喻

3
00:00:17,000 --> 00:00:20,000
若想对生物有完整的认识

4
00:00:20,000 --> 00:00:22,000
就要先深入了解演化的歷程

5
00:00:22,000 --> 00:00:26,000
大多人都对自然天择耳熟能详

6
00:00:26,000 --> 00:00:30,000
但天择只是
驱动演化歷程的五要素之一

7
00:00:30,000 --> 00:00:33,000
在探讨这五要素之前

8
00:00:33,000 --> 00:00:35,000
我们应先明白演化的定义

9
00:00:35,000 --> 00:00:38,000
演化指的是基因库裡随时间累积的变异

10
00:00:38,000 --> 00:00:42,000
那甚麼是基因库? 基因又是甚麼?

11
00:00:42,000 --> 00:00:45,000
在开始钻研遗传学之前

12
00:00:45,000 --> 00:00:47,000
我们先来说个故事

13
00:00:47,000 --> 00:00:52,000
想像有艘船翻覆了，
10 位生还者游到一座荒岛的岸边

14
00:00:52,000 --> 00:00:57,000
没有人来救他们，
他们形成一个繁衍数千年的聚落

15
00:00:57,000 --> 00:01:00,000
奇怪的是，其中 5 人是红髮

16
00:01:00,000 --> 00:01:05,000
红髮的特徵须经
父母双方各得一个红髮基因

17
00:01:05,000 --> 00:01:08,000
若仅有一个红髮基因，就不会表现红髮的特徵

18
00:01:08,000 --> 00:01:10,000
為了让情况更简单些，我们假设

19
00:01:10,000 --> 00:01:14,000
不是红髮的另外 5 人完全没有红髮基因

20
00:01:14,000 --> 00:01:16,000
因此红髮基因的最初机率是是50%

21
00:01:16,000 --> 00:01:20,000
也就是 20 个基因裡有10 个红髮基因

22
00:01:20,000 --> 00:01:22,000
这些基因就组成基因库

23
00:01:22,000 --> 00:01:25,000
20 个不同的基因就像一叠纸牌

24
00:01:25,000 --> 00:01:28,000
世代交替时就会重新洗牌一次

25
00:01:28,000 --> 00:01:32,000
交配就是让基因重新洗牌的机制

26
00:01:32,000 --> 00:01:36,000
这些洗过的牌会传递到下一代

27
00:01:36,000 --> 00:01:39,000
洗牌后还是有一半的红髮基因

28
00:01:39,000 --> 00:01:43,000
重新洗牌过的基因会传递到下一代

29
00:01:43,000 --> 00:01:47,000
基因库裡红髮的比率依旧维持50%

30
00:01:47,000 --> 00:01:50,000
虽然人口数量可能会与日俱增

31
00:01:50,000 --> 00:01:53,000
得到红髮基因的机会仍维持 50%

32
00:01:53,000 --> 00:01:56,000
一旦机率有了变异，演化就此发生

33
00:01:56,000 --> 00:02:00,000
演化指的是基因库裡随时间累积的变异

34
00:02:00,000 --> 00:02:02,000
从纸牌的角度来看

35
00:02:02,000 --> 00:02:05,000
如果得到纸牌的机率有了变异

36
00:02:05,000 --> 00:02:07,000
演化就发生了

37
00:02:07,000 --> 00:02:10,000
有 5 个因素能够造成机率改变

38
00:02:10,000 --> 00:02:15,000
我们运用 5 根手指以便於记忆这 5 项要素

39
00:02:15,000 --> 00:02:17,000
从小指开始数到大拇指

40
00:02:17,000 --> 00:02:21,000
小指代表可能缩小的族群


41
00:02:21,000 --> 00:02:24,000
一旦族群缩小，演化就可能发生

42
00:02:24,000 --> 00:02:28,000
假如一场瘟疫中只有 4 人倖存

43
00:02:28,000 --> 00:02:31,000
他们的基因就会成為新基因库

44
00:02:31,000 --> 00:02:33,000
接着是无名指 (婚戒指)

45
00:02:33,000 --> 00:02:38,000
无名指会提醒你择偶，
因为婚戒表示成双成对

46
00:02:38,000 --> 00:02:41,000
若个人依据外表或地缘来择偶

47
00:02:41,000 --> 00:02:43,000
基因库的机率就可能改变

48
00:02:43,000 --> 00:02:47,000
若红发个体仅和红发个体婚配

49
00:02:47,000 --> 00:02:49,000
他们自然形成新群落

50
00:02:49,000 --> 00:02:52,000
若无人愿与红发个体婚配

51
00:02:52,000 --> 00:02:54,000
红发基因数会减少

52
00:02:54,000 --> 00:02:55,000
再来是中指

53
00:02:55,000 --> 00:02:59,000
中指 (middle finger) 里的 "M"
会让人联想到突变 (Mutation) 的 "M"

54
00:02:59,000 --> 00:03:03,000
若突变产生新基因,
基因库的机率就会受影响

55
00:03:03,000 --> 00:03:07,000
想像一个新的基因变异创造出新发色

56
00:03:07,000 --> 00:03:10,000
基因库里的遗传机率会随之变化

57
00:03:10,000 --> 00:03:12,000
食指会让你想起动作或移动

58
00:03:12,000 --> 00:03:16,000
假如新个体流入或迁入区域内

59
00:03:16,000 --> 00:03:17,000
此区的基因库也会变动

60
00:03:17,000 --> 00:03:20,000
如果个体自某区外流或者移出

61
00:03:20,000 --> 00:03:22,000
基因库同样也会变动

62
00:03:22,000 --> 00:03:25,000
科学上称之为基因流动

63
00:03:25,000 --> 00:03:30,000
这 4 只手指代表的变因都能引发演化

64
00:03:30,000 --> 00:03:34,000
族群规模小，选择性交配

65
00:03:34,000 --> 00:03:37,000
基因突变和流动

66
00:03:37,000 --> 00:03:39,000
不过这些都不会导致演化适应

67
00:03:39,000 --> 00:03:41,000
天择是唯一的途径

68
00:03:41,000 --> 00:03:45,000
能让生物更适应所处环境

69
00:03:45,000 --> 00:03:48,000
我们用大拇指来记住这个要素

70
00:03:48,000 --> 00:03:52,000
大自然会对最适应环境的特征，
竖起大拇指说讚

71
00:03:52,000 --> 00:03:55,000
然后拇指朝下，淘汰无法适应环境的特征

72
00:03:55,000 --> 00:03:59,000
个体中无法适应环境的基因

73
00:03:59,000 --> 00:04:02,000
会逐渐被适应性较佳的基因淘汰

74
00:04:02,000 --> 00:04:05,000
红发只是众多性状的其中之一

75
00:04:05,000 --> 00:04:08,000
在较北方的气候区，红发人较具优势

76
00:04:08,000 --> 00:04:12,000
因为他们白皙的皮肤能吸收较多光线

77
00:04:12,000 --> 00:04:15,000
进而合成较多维生素D，真是讚!

78
00:04:15,000 --> 00:04:19,000
但是同样的红发在南方却是劣势

79
00:04:19,000 --> 00:04:23,000
因为过强的UV射线会导致癌症和降低受孕

80
00:04:23,000 --> 00:04:25,000
大扣分!

81
00:04:25,000 --> 00:04:29,000
其实就连拇指本身，
也是适应环和天择的产物

82
00:04:29,000 --> 00:04:34,000
以上所讨论的都是微观演化

83
00:04:34,000 --> 00:04:36,000
因为它牵涉到的都是小改变

84
00:04:36,000 --> 00:04:38,000
不过这样的演化可能

85
00:04:38,000 --> 00:04:41,000
最终会导向巨观演化，形成新物种

86
00:04:41,000 --> 00:04:46,000
地球上所有生物都源于一个共同的祖先

87
00:04:46,000 --> 00:04:49,000
所有地球上现存的生物都经由演化

88
00:04:49,000 --> 00:04:52,000
紧密相连，环环相扣

89
00:04:52,000 --> 00:04:53,000
看看你的双手

90
00:04:53,000 --> 00:04:58,000
这神奇杰作就是历经演化 5 要素的产物

91
00:04:58,000 --> 00:05:00,000
演化历程长达数百万年之久

92
00:05:00,000 --> 00:05:04,000
你能凭记忆说出引发演化的 5 个因素吗?

93
00:05:04,000 --> 00:05:07,000
不能的话，再回顾一次忘记的片段

94
00:05:07,000 --> 00:05:12,040
若你成功的话，和附近的人用力击掌吧!