The Five Fingers of Evolution.

五隻手指的進化

A thorough understanding of biology requires

要透徹的了解生物學需要

a thorough understanding of the process of evolution.

透徹地了解進化的過程

Most people are familiar with the process of natural selection.

大多人對天擇的歷程並不陌生

However, this is just one of five processes that can result in evolution.

然而，那只是能造就進化的五個歷程之一

Before we discuss all five of these processes,

在我們探討這五個歷程之前，

we should define evolution.

我們應該先定義進化

Evolution is simply change in the gene pool over time.

進化就是指基因庫隨時間而改變

But what is a gene pool? And for that matter, what is a gene?

但是何謂基因庫？更甚者，何謂基因？

Before spending any more time on genetics,

在花更多時間在基因學上之前，

let us begin with a story.

讓我們以一個故事作為開頭

Imagine that a boat capsizes, and 10 survivors swim to shore on a deserted island.

想像一艘船翻覆了，十位生還者游上一座無人島的岸邊

They are never rescued, and they form a new population that exists for thousands of years.

他們再也沒有被營救，並自成一個新的族群，生存了幾千年

Strangely enough, five of the survivors have red hair.

說也奇怪，五位生還者有著紅頭髮

Red hair is created when a person inherits two copies of the red gene from their parents.

紅色頭髮傳承自父母雙方的紅髮基因

If you only have one copy of the gene, you won't have red hair.

如果你只得到一份這種基因，你不會有紅頭髮

To make this easier, we will assume

為了讓事情簡單點，我們假設

that the five non-redheads are not carriers of the gene.

五位非紅髮的人並沒有這種基因

The initial frequency of the red hair gene

因此最初紅髮基因的機率

is therefore 50 percent, or 10 of 20 total genes.

是 50%，或者說所有基因的二十分之十

These genes are the gene pool.

這些基因即是基因庫

The 20 different genes are like cards in a deck

這二十個不同的基因就像是一副牌

that keep getting reshuffled with each new generation.

不斷在每個新的世代重新洗牌

Sex is simply a reshuffling of the genetic deck.

性簡單來說就是基因重新洗牌的過程

The cards are reshuffled and passed to the next generation;

卡片被重新洗牌並傳承至下一代；

the deck remains the same, 50 percent red.

這副牌維持不變，一樣是 50%的紅色

The genes are reshuffled and passed to the next generation;

基因被重新洗牌並傳承至下一代；

the gene pool remains the same, 50 percent red.

基因庫維持不變，一樣是 50%的紅色

Even though the population may grow in size over time,

即使人口數隨著時間逐漸成長，

the frequency should stay at about 50 percent.

機率分佈應該要維持在 50%

If this frequency ever varies, then evolution has occurred.

如果這個機率分佈有任何變動，表示有進化發生了

Evolution is simply change in the gene pool over time.

進化就是指基因庫隨時間而改變

Think about it in terms of the cards.

從卡牌的角度來思考看看

If the frequency of the cards in the deck ever changes,

如果一副牌的機率分佈有任何改變，

evolution has occurred.

進化已發生了

There are five processes that can cause the frequency to change.

造成機率分佈改變的歷程有五種

To remember these processes, we will use the fingers on your hands,

為了記住這些歷程，我們會用你的五隻手指作為代表，

starting from the little finger and moving to the thumb.

從小指開始到拇指

The little finger should remind you that the population can shrink.

小指告訴你人口可能會縮減

If the population shrinks, then chance can take over.

如果人口縮減了，機率分佈便轉而接管

For example, if only four individuals survive an epidemic,

例如，如果只有四個人從流行病中存活下來，

then their genes will represent the new gene pool.

他們的基因就代表了新的基因庫

The next finger is the ring finger.

下一隻手指是無名指

This finger should remind you of mating, because a ring represents a couple.

這隻手指代表了擇偶，因為戒指代表著伴侶

If individuals choose a mate based on their appearance or location,

如果一個人是基於對方的外表或地域來擇偶，

the frequency may change.

機率分佈便可能會改變

If redheaded individuals only mate with redheaded individuals,

如果紅髮的人只跟紅髮的人在一起，

they could eventually form a new population.

他們最終會成為一個新的族群

If no one ever mates with redheaded individuals,

如果沒有人要跟紅髮的人成為伴侶，

these genes could decrease.

這些基因可能會消失

The next finger is the middle finger.

下一隻手指是中指

The M in the middle finger should remind you of the M in the word "mutation."

「中指」(middle finger) 裡的字母M可以讓你聯想到突變 (mutation) 中的字母M

If a new gene is added through mutation, it can affect the frequency.

如果一個新的基因因突變而出現了，它會影響機率分佈

Imagine a gene mutation creates a new color of hair.

設想一個突變的基因創造出新的髮色

This would obviously change the frequency in the gene pool.

這理所當然地會影響基因庫中機率分佈

The pointer finger should remind you of movement.

食指讓你聯想到行動

If new individuals flow into an area, or immigrate,

如果新的一批人流進入一個區域，或者移民，

the frequency will change.

機率分佈便會改變

If individuals flow out of an area, or emigrate,

如果人流移出一個區域，或者遷徙，

then the frequency will change.

機率分佈會隨之改變

In science, we refer to this movement as gene flow.

在科學領域，我們稱這樣的改變為基因流動

All four of the processes represented by our fingers can cause evolution.

我們四隻手指所代表的歷程皆會導致進化

Small population size, non-random mating,

小型人口數、非隨機的擇偶、

mutations and gene flow.

突變以及基因流動

However, none of them lead to adaptation.

然而，這其中沒有任何一個能造就適應性

Natural selection is the only process

天則是唯一

that creates organisms better adapted to their local environment.

能讓生物體更加適應於其周遭環境的歷程

I use the thumb to remember this process.

我用大拇指來記住這個歷程

Nature votes thumbs up for adaptations that will do well in their environment,

大自然會對那些適宜環境的適應質表示讚許，

and thumbs down to adaptations that will do poorly.

但對表現不佳的適應質表示否決

The genes for individuals that are not adapted for their environment

在所屬環境適應不良的個體基因

will gradually be replaced by those that are better adapted.

會逐漸被適應良好的取代

Red hair is an example of one of these adaptations.

紅頭髮是適應質的其中一個例子

Red hair is an advantage in the northern climates,

紅頭髮在北方的氣候中是一個優勢，

because the fair skin allowed ancestors to absorb more light

因為白皙的皮膚使得祖先們可以吸收更多的光

and synthesize more vitamin D. Thumbs up!

並形成更多維他命 D。給個讚！

However, this was a disadvantage in the more southern climates,

然而，這在南方的氣候中卻形成一個劣勢，

where increased UV radiation led to cancer and decreased fertility.

更多的紫外線輻射會導致癌症和生育率下降

Thumbs down!

否決！

Even the thumb itself is an adaptation formed through the process of natural selection.

即使是拇指本身，也是一個天擇後留下的適應質

The evolution that we have described is referred to as microevolution,

我們所描述的進化只是所謂的微進化，

because it refers to a small change.

因為它只涉及微小的改變

However, this form of evolution may

然而，這樣的進化也可能

eventually lead to macroevolution, or speciation.

逐漸演變成大進化，或新物種形成

Every organism on the planet shares ancestry with a single common ancestor.

地球上每個生物體都與一個共同的祖先流著相同血液

All living organisms on the planet are connected back in time

活在地球上的所有生物體在時間線上都是相連著的

through the process of evolution.

透過進化的過程

Take a look at your own hand.

看看你自己的手

It's an engineering masterpiece that was created by the five processes I just described,

這是一項工程上的巨作，藉由我剛才介紹的五個歷程所創造出的，

over millions and millions of years.

經過數以百萬年的時間

Can you recall the five main causes of evolution from memory?

你可以回想出那五個造成進化的主要原因嗎？

If you can't, hit rewind and watch that part again.

如果不行，按下倒轉然後重新看一次那一段

But if you can, give yourself or your neighbor a big five-fingered high five.

但如果你做得到，跟你自己或是身旁的人大大地擊掌吧！