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生命进化的原理

How Evolution works

进化机制
Mechanisms of evolution
什么是进化
What is evolution?
进化是地球生命的发展过程
Evolution is the development of life on Earth.
其始于数十亿年前 并持续至今
This is a process that began billions of years ago and is still continuing to this day.
进化揭示了生命多样发展的可能性
Evolution tells us how it was possible for the enormous diversity of life to develop.
也展现了原始的原生动物是如何能够演变成我们今天看到的数百万的不同的物种
It shows us how primitive Protozoa could become the millions of different species that we see today.
进化能解答我们的如下疑问 当我们看到腊肠犬和大丹犬在一起时
Evolution, then, is the answer to the question that we have all asked on seeing a Daschund and a Great Dane together:
我们会奇怪: 后代和祖先怎么会长得如此不同
how is it possible for ancestors to have descendants that look so very different to them?
回答这个问题时 让我们将注意力放在动物上 暂且忽略菌类和植物等其他生命形式
In answering this question, we want to focus on animals, excluding other forms of life such as fungi and plants.
那么 第一个问题是 一种动物如何能演变成一种全新的动物
The first question to ask is therefore: how can one animal develop into a whole new species of animal?
对了 快速回答下 物种究竟是什么
Ah, but just a quick question: what exactly is a species?
物种是一群能够一起繁衍后代的个体
A species is a community of animals that is capable of producing offspring with one another,
而这些后代也能继续繁殖
with those offspring also being capable of reproducing in turn.
为了更好地理解这一概念 我们来详细了解下以下要点
To understand this answer better, we need to take a closer look at the following points:
生物的独特性通过过度繁殖和遗传得以保留
the uniqueness of living creatures, guaranteed through the excess production of offspring and heredity,
第二个重要因素是自然选择
and as a second key point, selection.
让我们先来看看独特性 每种存在的生物都是独特的 这是进化的基本要素
Let’s begin with uniqueness. Every creature that exists is unique, and this is essential for evolution.
同一个物种中的个体 可能外观上彼此非常相似
The members of a species may strongly resemble each other in appearance;
但是 每个个体在特征上总会有一些细微的差异
however, they all have slightly different traits and characteristics.
他们可能比同类更大 更胖 更强壮 或者更大胆
They may be a bit bigger, fatter, stronger, or bolder than their fellow animals.
那么 是什么导致了这些差异呢 让我们更仔细来了解下生物个体
So, what is the reason for these differences? Let’s take a closer look at a creature.
每个生物都是由细胞构成的 细胞都有一个细胞核
Every creature is made up of cells. These cells have a nucleus.
细胞核中有染色体 而染色体携带着DNA
The nucleus contains the chromosomes, and the chromosomes hold the DNA.
DNA由不同的基因组成 这些基因正是生命信息的携带者
DNA consists of different genes, and it’s these genes that are life’s information carriers.
基因包含了细胞的结构和顺序 决定了生物的特征
They contain instructions and orders for the cells, and determine the characteristics and traits that living creatures have,
准确地说 每个生物的DNA都是独一无二的
and it’s precisely this DNA that is unique to every creature.
个体间DNA的细微的差异就是个体特征差异的原因
It’s slightly different from individual to individual, which is why each has slightly different characteristics.
那么 不计其数的DNA是如何被创造出来的呢
But how is the enormous range of DNA created?
一个重要因素就是繁殖过盛
One key factor is the excess production of offspring.
在自然界中 我们能看到 生物的繁殖量往往多于该物种维持生存必需的数量
In nature, we can observe that creatures generally produce far more offspring than is necessary
这样导致许多后代过早死亡
for the survival of their species, with many offspring dying an early death as a result.
而且 常常 生物的数量甚至超过了居住环境所能承载的数量
Often there are even more offspring than the environment in which they live is able to support.
这是物种多样性增加的原因之一
This is one factor in increasing diversity within a species.
繁衍越多 细小的差异越多
The more offspring that are produced, the more little differences occur,
这正是自然发展的趋势  细小差异不断增多
and this is what nature wants: as many little differences as possible.
导致个体独特性的第二个因素在于遗传本身
The second major cause of the uniqueness of individuals occurs in heredity itself.
顺便提一下 遗传是指DNA在后代身上的传递
By the way, heredity means the passing on of DNA to offspring.
在这个过程中 两个有趣的因素发挥了作用 重组和突变
Two very interesting factors come into play in this process: recombination and mutation.
重组是两个生物的DNA随机组合
Recombination is the random mixing of the DNA of two creatures.
当两个生物相爱并交配时 他们的基因会经历两次重组
When two creatures fall in love and mate, they recombine their genes twice.
第一次是在 它们各自产生配子的时候 即精子和卵细胞
The first time, they do this separately when they generate the gametes – that is, sperm and egg cells.
配子带走一半的基因并重组
The gametes take half of the genes and shuffle them.
第二次重组发生在雄性让雌性受孕的时候
The second recombination occurs when a male inseminates a female.
父母各提供50%的DNA  也就是说它们50%的特征
The parents each provide 50% of their DNA, in other words, 50% of their unique traits and characteristics.
这些特征再次重组或混合 然后繁衍出后代
These are then recombined, or mixed, and the result is new offspring.
这些后代拥有随机组合的DNA 因此也就拥有了父母的特征
These offspring have a random mix of the DNA, and therefore the traits and characteristics of their parents.
这一过程大大增加了物种内的的多样性和差异性
This increases the diversity and differences within a species even further,
同时 突变对进化也起着非常重要的作用
but mutations are also important for evolution.
突变是DNA的随机变化
Mutations are random changes in DNA.
它们也被称作是DNA的复制错误
These can also be described as copying errors within the DNA,
毒素 化学物质或者辐射都可能会引起突变
triggered by toxins or other chemical substances, or by radiation.
部分DNA改变的时候 突变就发生了
A mutation exists when part of the DNA is altered.
这些改变通常是消极的 可能导致癌症等疾病
These changes are often negative, and may result in illnesses such as cancer.
但是 它们也可能产生中性或积极的作用
However, they may also have neutral or positive effects,
像人类的蓝色眼睛就是一种基因突变
such as the blue eye colour in humans, which is one such random mutation.
所有的遗传突变中 配子 即精子和卵细胞 会受到影响
In all cases, a mutation has to affect a gamete, that is a sperm or egg cell,
因为只有配子中的DNA会传递给后代
because only the DNA in the gametes is passed on to the offspring.
这也是我们在做x光检查时保护我们性器官的原因 而身体其他部分并不会存在风险
This is also the reason why we protect our sexual organs during x-rays, whilst other parts of the body are not at risk.
所以 结论是 在遗传过程中 生物自身的特征以DNA的形式传递给他们的后代
In summary then, in the heredity process, creatures pass on their characteristics to their offspring in the form of DNA.
而重组和突变改变了DNA 因此兄弟姐妹间外观存在差异
Recombination and mutation change the DNA so that each child looks different to its siblings,
他们随机继承了父母的特征
and receives a random mix of the characteristics of its parents.
这有个关键词 随机
There’s a key word here: random.
对 所有这些过程都是基于机会的
All of these processes are based on chance.
随机重组和突变导致个体随机获得各种特征
Random recombination and mutations result in individuals with random mixes of traits and characteristics,
而这些特征又再次随机组合并传递给下一代
which in turn mix these randomly, and pass them on.
那么  这些几率是如何发生的呢毕竟每种生物都能完美适应环境
But how can so much be down to chance, when all living creatures are so perfectly adapted to their environment,
比如 竹节虫 蜂鸟和躄鱼
for example, the stick insect, the hummingbird, and the frogfish?
答案就是 自然选择 影响进化的第二个重要因素
The answer is provided by the second key point: selection.
每个个体都要经历自然选择的过程
Each individual is subjected to a process of natural selection.
正如我们之前了解的 每个个体或多或少和同类有些差异
As we have learned, each individual is somewhat different to its fellows,
每个物种内都存在丰富的多样性
and there is extensive variation within a species.
环境影响生物 这些所谓的选择因素包括
Environmental influences have an effect on living creatures. These so-called selection factors include:
食肉动物 寄生虫 同物种动物 毒质 栖息地或气候的变化
predators, parasites, animals of the same species, toxins, changes in habitat, or the climate.
每个个体都要接受自然选择
Selection is a process that each individual is subjected to.
每个生物都有独特混合的特征
Every creature has a unique mix of traits and characteristics.
这种组合能帮助他们适应环境得以生存 也可能导致不适应从而灭亡
This mix helps them to survive in their environment, or not, as the case may be.
所有带有不适宜组合特征的生物将被环境淘汰
Anyone with an unsuitable mix will be selected from the environment.
拥有适宜特征的物种得以生存并繁殖后代 传递并增强它们的特征
Those with the right mix survive, and can pass on their enhanced traits and characteristics.
这正是多样性如此重要的原因
This is why diversity is so important.
由此 生物努力繁衍后代 尽可能得差异化
This is why creatures make so much effort to produce offspring that are as different as possible.
他们借此增加至少有一个后代能通过自然选择的可能性
They increase the likelihood that at least one of their offspring passes nature’s selection process.
使生存机会最大化
They maximize their chances of survival.
生活在荒岛的成群雀鸟是个很好的例子
A good example of this can be seen in a group of finches living on a remote island.
它们是科学世界里最有名的动物之一
They are some of the most famous animals in the world of science,
它们也被称作达尔文鸟 是达尔文发现了它们接下来我们要说到雀鸟的故事
and are known as Darwin finches, after their discoverer, Charles Darwin, and this is the story of those finches.
几百年前 很有可能是一场暴风雨将小群雀鸟吹到了太平洋中的加拉帕戈斯群岛
A few hundred years ago, a small group of finches was blown onto the Galapagos Islands in the middle of the Pacific, probably by a big storm.
对这些雀类来说 这里完全是个新大陆
The finches found themselves in an environment that was completely new to them,
一个真正的雀鸟天堂: 充足的食物 而且没有任何天敌
a real finch paradise: an abundance of food and no predators.
他们快速繁殖 数量激增  这些岛屿很快被雀鸟沾满
They reproduced rapidly and numerously. The islands were soon heaving with finches.
这意味着 食物越来越稀缺
This meant that food supplies became increasingly scarce.
雀鸟天堂面临饥荒的威胁 雀与雀也从朋友变成了竞争者
The finch paradise was threatened with famine, and finch friends became competitors.
这时 自然选择发挥了作用
This is when selection intervened.
鸟喙变得不同
Their individuality and small differences, in this case their slightly different beaks,
这样的特征和细小差异使得一些雀鸟能避免和同类竞争
meant that some of the birds were able to avoid competing with their fellow finches.
有些雀鸟的喙更适合挖虫子吃
The beaks of some of the finches were more suitable for digging for worms.
有些雀鸟可以用喙来剥种子吃
Other finches were able to use their beaks better for cracking seeds.
这些雀鸟分离出不同的生态位 在生态位内 它们免于过多的竞争
The finches consequently sort out ecological niches. In these niches, they were safe from excessive competition.
很快 它们开始主要和同一个生态位的其他雀鸟交配
They soon began to mate primarily with other finches that used the same niche.
经过一代又一代的繁衍 这些特征得以巩固
Over the course of many generations, these characteristics were enhanced,
雀鸟成功得开拓了它们的生态位 更好地适应了环境
enabling the finches to exploit their niches successfully.
吃虫雀鸟和吃种子雀鸟的差异越来越大
The differences between the worm-diggers and the seed-crackers became so large
因此 它们不再和彼此交配 不同的物种由此出现
that they were no longer able to mate with one another. Different species emerged as a result.
如今 加拉帕戈斯群岛生活着14种不同的雀类
Today, there are 14 different species of finch living on the Galapagos Islands,
它们有着相同的祖先 就是最初那群搁浅在群岛的雀鸟们
all of which are descended from the same group of stranded finches.
这就是进化产生新物种的过程:
This is how new species are created by evolution:
通过不同个体的相互作用
through the interaction of unique individuals,
过度繁衍后代
the excess production of offspring,
遗传的重组和突变
recombination and mutation in heredity,
最终 通过自然选择 产生新的物种
and finally, through selection.
这为什么如此重要呢
Why is this so important?
因为它揭示了我们生命多样性的起源 生物能完美适应环境的原因
It tells us where the variety of life comes from, and why living creatures are so perfectly adapted to their habitats.
同样 进化也影响着我们人类
But it also effects us personally.
每个人都是35亿年进化的产物  包括你
Every person is the result of 3.5 billion years of evolution, and that includes you.
祖先不断斗争 适应环境 得以生存
Your ancestors fought and adapted in order to survive.
生存存在极大的不确定性
This survival was an extremely uncertain thing.
想想 事实上 99%曾经生存的物种都已灭绝
If we consider the fact that 99% of all the species that have ever lived are extinct,
人类能生存下来 可以说是一部成功史
then you can consider yourself part of a success story.
恐龙已经灭绝了 而你还活着 在看这个视频
The dinosaurs have disappeared, but you are alive, watching this video,
因为你非常独特 正就像现在存活的其他生物一样
because you’re incredibly special, just like all the other creatures that exist today:
是宇宙中不可复制且独一无二的存在
irreproducible and unique in the universe.

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