Mechanisms of evolution
What is evolution?
Evolution is the development of life on Earth.
This is a process that began billions of years ago and is still continuing to this day.
Evolution tells us how it was possible for the enormous diversity of life to develop.
It shows us how primitive Protozoa could become the millions of different species that we see today.
Evolution, then, is the answer to the question that we have all asked on seeing a Daschund and a Great Dane together:
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?
A species is a community of animals that is capable of producing offspring with one another,
with those offspring also being capable of reproducing in turn.
To understand this answer better, we need to take a closer look at the following points:
the uniqueness of living creatures, guaranteed through the excess production of offspring and heredity,
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.
The members of a species may strongly resemble each other in appearance;
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.
Every creature is made up of cells. These cells have a nucleus.
The nucleus contains the chromosomes, and the chromosomes hold the DNA.
DNA consists of different genes, and it’s these genes that are life’s information carriers.
They contain instructions and orders for the cells, and determine the characteristics and traits that living creatures have,
and it’s precisely this DNA that is unique to every creature.
It’s slightly different from individual to individual, which is why each has slightly different characteristics.
But how is the enormous range of DNA created?
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
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.
This is one factor in increasing diversity within a species.
The more offspring that are produced, the more little differences occur,
and this is what nature wants: as many little differences as possible.
The second major cause of the uniqueness of individuals occurs in heredity itself.
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.
Recombination is the random mixing of the DNA of two creatures.
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.
The gametes take half of the genes and shuffle them.
The second recombination occurs when a male inseminates a female.
The parents each provide 50% of their DNA, in other words, 50% of their unique traits and characteristics.
These are then recombined, or mixed, and the result is new offspring.
These offspring have a random mix of the DNA, and therefore the traits and characteristics of their parents.
This increases the diversity and differences within a species even further,
but mutations are also important for evolution.
Mutations are random changes in DNA.
These can also be described as copying errors within the DNA,
triggered by toxins or other chemical substances, or by radiation.
A mutation exists when part of the DNA is altered.
These changes are often negative, and may result in illnesses such as cancer.
However, they may also have neutral or positive effects,
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,
because only the DNA in the gametes is passed on to the offspring.
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.
Recombination and mutation change the DNA so that each child looks different to its siblings,
and receives a random mix of the characteristics of its parents.
There’s a key word here: random.
All of these processes are based on chance.
Random recombination and mutations result in individuals with random mixes of traits and characteristics,
which in turn mix these randomly, and pass them on.
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.
Each individual is subjected to a process of natural selection.
As we have learned, each individual is somewhat different to its fellows,
and there is extensive variation within a species.
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.
Selection is a process that each individual is subjected to.
Every creature has a unique mix of traits and characteristics.
This mix helps them to survive in their environment, or not, as the case may be.
Anyone with an unsuitable mix will be selected from the environment.
Those with the right mix survive, and can pass on their enhanced traits and characteristics.
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.
They increase the likelihood that at least one of their offspring passes nature’s selection process.
They maximize their chances of survival.
A good example of this can be seen in a group of finches living on a remote island.
They are some of the most famous animals in the world of science,
and are known as Darwin finches, after their discoverer, Charles Darwin, and this is the story of those finches.
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.
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.
This meant that food supplies became increasingly scarce.
The finch paradise was threatened with famine, and finch friends became competitors.
This is when selection intervened.
Their individuality and small differences, in this case their slightly different beaks,
meant that some of the birds were able to avoid competing with their fellow finches.
The beaks of some of the finches were more suitable for digging for worms.
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.
They soon began to mate primarily with other finches that used the same niche.
Over the course of many generations, these characteristics were enhanced,
enabling the finches to exploit their niches successfully.
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.
Today, there are 14 different species of finch living on the Galapagos Islands,
all of which are descended from the same group of stranded finches.
This is how new species are created by evolution:
through the interaction of unique individuals,
the excess production of offspring,
recombination and mutation in heredity,
最终 通过自然选择 产生新的物种
and finally, through selection.
Why is this so important?
It tells us where the variety of life comes from, and why living creatures are so perfectly adapted to their habitats.
But it also effects us personally.
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.
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,
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,
because you’re incredibly special, just like all the other creatures that exist today:
irreproducible and unique in the universe.