Part 3

Evolution Natural selection, in which good mutations are passed on, changes living things and can lead to brand new species! This is called evolution, and it usually happens slowly, over millions of years. Darwin's finches Darwin realized that the different types of finch on the Galápagos Islands were all related. However, they had differently shaped beaks, depending on where they lived on the islands. Each beak had become specially adapted for, or suited to, eating different kinds of food. Charles Darwin In 1831, the scientist Charles Darwin sailed to South America. On his voyage, he saw lots of weird animals and plants that he'd never seen before. He started to wonder where they all came from. Changing beak Since Darwin, this finch's diet has changed from soft seeds to larger, harder ones. To cope with this, its beak has evolved to become bigger! FACT FILE » Scientific name: Geospiza magnirostris » Beak: Bulky and powerful » Diet: Large nuts and seeds FACT FILE » Scientific name: Geospiza fortis » Beak: Strong and deep » Diet: Seeds A voyage of discovery Darwin's voyage, aboard a ship called HMS Beagle, took him to the Galápagos Islands, west of South America. Based on what he saw, Darwin realized that all life on Earth must be connected. He wrote about his ideas in a book called On the Origin of Species. Darwin's ship HMS Beagle sailed to South America to plot maps. The ship's captain, Robert FitzRoy, took Darwin to study wildlife. FACT FILE » Scientific name: Camarhynchus parvulus » Beak: Small and sharp » Diet: Insects FACT FILE » Scientific name: Certhidea olivacea » Beak: Pointed for foraging under bark » Diet: Small insects and spiders

演化 自然选择就是保留有利突变，改变生物样貌，还能孕育出全新的物种哦！ 这就叫做演化，它通常发生得十分缓慢，要历经数百万年的时间。 达尔文的雀鸟 达尔文发现，加拉帕戈斯群岛上不同种类的雀其实都有亲缘关系。 不过，根据它们生活的岛屿环境不同，雀的喙形状也各不相同。 每一种喙都经过特殊演化，刚好适合食用不同种类的食物。 查尔斯·达尔文 1831年，科学家查尔斯·达尔文乘船前往南美洲。 航行途中，他见到了许多从未见过的奇特动植物。 他开始好奇这些生物究竟来自哪里。 改变的喙 自达尔文的时代后，这种雀的食性发生了变化，从吃软种子改成吃更大更硬的种子。 为了适应这种变化，它的喙慢慢演化得更大了！ 资料卡 » 学名：大喙地雀 Geospiza magnirostris » 喙：粗壮有力 » 食性：大型坚果和种子 资料卡 » 学名： 中嘴地雀 Geospiza fortis » 喙：粗壮深厚 » 食性：种子 发现之旅 达尔文搭乘名为“小猎犬号”的船航行，来到了南美洲西侧的加拉帕戈斯群岛。 根据自己的观察，达尔文意识到地球上所有生命一定都是相互关联的。 他把自己的观点写进了《物种起源》这本书中。 达尔文乘坐的小猎犬号航行到南美洲原本是为了绘制地图。 船长罗伯特·菲茨罗伊邀请达尔文一同研究野生生物。 资料卡 » 学名：小树雀 Camarhynchus parvulus » 喙：小巧锋利 » 食性：昆虫 资料卡 » 学名：绿莺雀 Certhidea olivacea » 喙：尖锐锋利，适合在树皮下方觅食 » 食性：小型昆虫和蜘蛛

How new species form When mutations appear in their DNA, living things evolve through natural selection. New species form from other species when many mutations change how they look or live. The Tree of Life Charles Darwin came up with the idea of the Tree of Life, showing how all living things are related to one another. Natural selection sends organisms off in many different directions, so there are lots of different branches. Chloroplasts These evolved to turn energy from sunlight into food. DNA DNA appeared early in the history of life. RNA world The tree of life grew from a soupy world of RNA life-forms External skeleton The animals on this branch have an external skeleton, or exoskeleton. Hair Great for keeping warm, hair is found only on this branch. Organs Organs evolved as cells grouped together to perform particular tasks. Nervous system Advanced animals had to evolve a system to feel and sense things. Backbone Animals with a backbone, or spine, are called vertebrates. Animals without a backbone are called invertebrates. Mitochondria and nuclei Some early cells evolved mitochondria, to give them energy, and a nucleus. All organisms share a common ancestor that lived four billion years ago.

新物种如何形成 当DNA发生突变后，生物就会通过自然选择发生演化。 当大量突变改变了生物的外形和生活方式，就会从原有物种中孕育出新物种。 生命之树 查尔斯·达尔文提出了生命之树的概念，用来展示所有生物之间的亲缘关系。 自然选择让生物往不同方向演化，因此生命之树长出了许许多多不同的分支。 叶绿体 叶绿体演化出来后，就能把太阳光的能量转化为生物所需的养分。 DNA DNA在生命历史的早期就已经出现了。 RNA世界 生命之树从充满RNA生命的原始汤中生长而来 外骨骼 这个分支的动物都拥有外骨骼。 毛发 毛发能很好地保暖，只有这个分支的动物才有毛发。 器官 细胞聚集在一起分工完成特定工作，就演化出了器官。 神经系统 高等动物演化出神经系统，用来感知周围的事物。 脊椎 拥有脊椎的动物被称为脊椎动物。 没有脊椎的动物则被称为无脊椎动物。 线粒体与细胞核 一些早期细胞演化出了提供能量的线粒体，还有细胞核。 所有生物都源自同一个共同祖先，它生活在四十亿年前。

Shared genes Some genes are so similar between different species that they can be swapped around by scientists and still work. Human genes can even work in the fungus yeast! Primates are closely related to rodents, such as mice. We shared an ancestor about 80 million years ago, and we have the same mammal characteristics, such as hair. Cows and humans are both mammals. We both have bony skeletons and hair and we breathe air, but we look very different. Cats have 19 pairs of chromosomes in their cells, whereas humans have 23 pairs. Many of the genes on them are the same though. One of our closest living relatives is the chimpanzee. We are both primates, and we have a common ancestor who lived about five million years ago. THAT'S BANANAS We share 50 percent of our genes with bananas! All animals and plants share a common ancestor—a single-celled life- form that lived more than a billion years ago. Many of the chemical processes that organisms need to survive are the same, so the genes that code for them are very similar. We don't share as many genes with insects as we do with vertebrates. However, some genes, such as the ones that put your head, body, and legs in the right order, are similar. We are family? We like to think that as a species humans are unique, but, actually, we share a lot of genes with other animals. In fact, we are more closely related to some species of apes than they are to each other! Humans are related to all living things, but we are most closely related to each other. All the things that make each person different, such as eye color, are due to differences in just 0.1 percent of our genes.

共享的基因 不同物种间有些基因非常相似，科学家将它们互换后依然能正常工作。 人类的基因甚至可以在酵母菌里发挥作用哦！ 灵长类和啮齿类（比如老鼠）的亲缘关系很近。 我们大约在八千万年前拥有共同祖先，也都具备哺乳动物的特征，比如长有毛发。 牛和人类都属于哺乳动物。 我们都有骨骼、长毛发、呼吸空气，但外形却相差很大。 猫的细胞里有19对染色体，人类则有23对。 不过，染色体上的许多基因都是相同的。 黑猩猩是现存和我们亲缘关系最近的亲戚之一。 我们都属于灵长类，大约五百万年前拥有共同的祖先。 想不到吧！我们和香蕉共享了50%的基因！ 所有动植物都源自同一个共同祖先——那是一种单细胞生物，生活在十亿多年前。 生物生存所需的许多化学反应都是相同的，因此编码这些反应的基因也十分相似。 我们和昆虫共享的基因，比和脊椎动物共享的要少。 不过，有些基因十分相似，比如负责让头、身体、腿按正确顺序生长的基因。 我们是一家人？ 我们总觉得人类这个物种是独一无二的，但实际上，我们和其他动物共享了很多基因。 事实上，人类和某些猿类的亲缘关系，比那些猿类之间的亲缘关系还要近！ 人类和所有生物都有亲缘关系，但我们人与人之间的亲缘关系最近。 所有让每个人各不相同的特征，比如眼睛颜色，都仅仅来自基因中0.1%的差异。

Model organisms Living things that are very easy to study in a laboratory are called model organisms. Here are some on these laboratory shelves! They're like a collection of useful creatures that helps us understand how biology works. Thale cress Arabidopsis thaliana, or thale cress, is a plant widely used to study crops and plant health. Fruit flies The fruit fly D. melanogaster has been studied in the lab for more than 100 years. A mutation in a gene known as antennapedia can cause legs to grow where the antennae should be! Fission yeast Scientists have learned a lot about how cells divide by studying this yeast (S. pombe). It has a mutant form that keeps growing but can't divide! Learning from each other We share a lot of our DNA with other living things. So, if we can understand how a gene works in another animal, plant, or even a fungus, we can get a good idea of how that gene might work in us. C. elegans worms have only 959 body cells. Nematode worm C. elegans is a tiny—just 0.04 in (1 mm) long—nematode worm that lives in rotting fruit. It is used to study lots of biological processes. Mice Mice (Mus musculus) are very useful because they are mammals, like us. We know from studies on mice that you need a gene that makes a protein called leptin to store fat properly. Mice with a faulty leptin gene get very fat. GFP The jellyfish gene makes a glow-in-the- dark protein called green fluorescent protein (GFP). The protein glows when you shine ultraviolet light on it. Jellyfish GFP was isolated from the glow-in- the-dark jellyfish Aequorea victoria. See-through Nematodes are transparent, and so it is easy to see which cells glow with GFP. Jellyfish gene Jellyfish have a gene that lets them glow in the dark. Scientists can borrow this gene and attach it to genes in other animals, such as the nematode C. elegans. When the gene being studied is active, scientists can see which cells it affects because they will glow.

模式生物 在实验室里非常容易研究的生物被叫做模式生物。 这些实验架上就摆着好几种哦！ 它们就像一座有用的生物宝库，帮我们弄清楚生物学的运作原理。 鼠耳芥 学名阿拉伯芥，又叫鼠耳芥，被广泛用来研究农作物和植物健康。 果蝇 黑腹果蝇已经在实验室被研究了一百多年了。 有一种叫触角足的基因如果发生突变，本该长触角的地方会长出腿哦！ 裂殖酵母 科学家通过研究裂殖酵母，了解到了很多细胞分裂的知识。 它有一种突变型只会不停长大，却不会分裂！ 知识共通 我们和其他生物有很多DNA是相同的。 所以只要我们弄清楚某个基因在其他动物、植物甚至真菌里的作用，就能推测出它在我们人体内大概如何工作。 秀丽隐杆线虫全身只有959个体细胞。 线虫小知识 秀丽隐杆线虫是一种极小的线虫——只有1毫米长，生活在腐烂的水果中。 它被用来研究很多种生物学过程。 小鼠 小家鼠和我们一样是哺乳动物，所以非常适合做研究。 从小鼠研究中我们得知，我们需要一个基因来合成瘦素蛋白，才能正常储存脂肪。 瘦素基因出问题的小鼠会变得非常胖。 绿色荧光蛋白（GFP） 水母的这个基因能合成一种会在黑暗中发光的蛋白，叫做绿色荧光蛋白（GFP）。 用紫外线照射这种蛋白，它就会发光。 绿色荧光蛋白是从会发光的维多利亚多管发光水母中分离出来的。 透明好观察 线虫本身是透明的，所以很容易看到哪些细胞带着GFP发光。 水母的发光基因 水母体内有一种能让自己在黑暗中发光的基因。 科学家可以提取这个基因，把它连接到其他动物的目标基因上，比如秀丽隐杆线虫。 当被研究的基因启动工作时，科学家就能通过发光看出它影响了哪些细胞。

Bad mutations Mutations that change DNA sequences can stop genes from working properly. This may mean that a protein can't be made or, if it can still be made, it doesn't work. Mutations in pets Humans like to create breeds of pets with characteristics that they find attractive. This selective breeding means that some pets have mutations that make them less healthy compared to their wild relatives. Is it right to keep these breeds going? Breathing difficulties People find pugs" flat faces cute, but their squashed noses often cause them breathing problems. Easy prey Albino animals don't produce any colored pigments. They are spotted more easily by predators and are at risk of sunburn. Feeling cold Hair is important in the wild for warmth, protection, and camouflage. Hairless pets need to be kept warm or they will suffer. COLOR-BLINDNESS Color-blindness means that you can't see different colors, as in the test picture (right). People with the most common type, called red-green color-blindness, can't see the green squiggly line. This condition is more common in boys than girls. Joint problems These cats have mutant cartilage that folds their ears. It also causes severe arthritis—pain, stiffness, and swelling in the joints. Deadly double The mutation in dwarf rabbits makes them very small. However, if a baby rabbit inherits two copies of the mutant gene, it won't survive. Fluff, not feathers! This breed's mutant fluffy feathers are not waterproof and are useless for flight. Silkies also have a gap in their skulls that makes their heads fragile.

有害突变 改变DNA序列的突变可能会让基因无法正常工作。 这可能导致没法合成相应的蛋白质，或是合成的蛋白质没法发挥作用。 宠物的突变 人类培育出了很多符合人类审美特征的宠物品种。 这种定向选育意味着，有些宠物携带的突变让它们比野生同类更不健康。 继续培育这些品种，这样做是对的吗？ 呼吸困难 人们觉得巴哥犬的扁脸很可爱，但它们挤窄的鼻腔常常会引发呼吸困难。 更容易被捕食 白化动物无法合成任何有色色素。 它们更容易被天敌发现，还更容易被晒伤。 容易受凉 在野外，毛发可以保暖、防护还能伪装，作用非常大。 无毛宠物必须做好保暖，不然会难受生病。 色盲 色盲就是无法分辨不同的颜色，就像右侧测试图展示的这样。 最常见的红绿色盲患者，没法看出图里绿色的波浪线。 这种症状在男孩中比女孩更常见。 关节问题 有些猫因为软骨突变，形成了折耳的性状。 这种突变还会引发严重的关节炎，让关节疼痛、僵硬还肿胀。 致命的双份突变 侏儒兔的突变让它们体型变得很小。 但如果幼兔同时继承了两份突变基因，就没法存活下来。 是绒毛，不是正羽！ 这个品种的突变绒毛不防水，也没法用来飞行。 丝羽乌骨鸡的头骨还有缺口，让它们的头部非常脆弱。

Faulty genes in us If a mutation alters the DNA sequence of your genes, this tiny change can sometimes cause big problems for the cells in your body. This is called a genetic disorder. Point mutations A change of just one DNA base is called a point mutation, and it can cause a genetic disorder, such as cystic fibrosis. In this disorder, cells that line the lungs don't work properly, and the lungs get clogged with thick, sticky mucus. DNA sequence in a healthy gene This sequence of DNA bases is from a healthy gene that makes a functioning protein. DNA sequence with a point mutation Just one change in the DNA sequence may have a big effect. It might stop a gene from making a protein, or cause the gene to make a protein that doesn't work properly in the body. Mutations are inherited in families when they are copied into eggs or sperm. Cancer Cancer is a genetic disorder caused by DNA mutations. However, it is only passed on through families when the cells with the cancer-causing mutations make sperm or eggs—which is rare. Causes of mutations Mutations can be caused by energy absorbed into cells, as well as by errors in DNA replication. Strong sunlight on skin cells may lead to mutations. Uncontrolled growth Mutations can cause cell division to go out of control, producing too many cells in one place. These extra cells form masses, called tumors. Invasion Cancerous tumors can invade other tissues and spread around the body. They stop it from working normally and can make you very sick. White blood cells A part of our immune system, white blood cells act like soldiers, finding and attacking enemy cells, including cancer cells. Cancer cell Some cancer cells can hide from white blood cells. However, new cancer drugs can boost the immune system and help find and fight the cancer. SICKLE CELL ANEMIA Two copies of a bad sickle-cell mutation cause red blood cells to change their shape and block blood vessels (tubes in your body that carry blood). However, one mutant version of the gene, together with a healthy copy, protects you against the disease malaria!

我们体内的缺陷基因 如果突变改变了你基因中的DNA序列，这种微小改变有时会给你体内的细胞带来大麻烦 这就被称为基因遗传病 点突变 仅仅一个DNA碱基的改变就叫做点突变，它会引发基因遗传病，比如囊性纤维化 得了这种病后，肺内壁细胞无法正常工作，肺部会被又稠又黏的黏液堵住 健康基因的DNA序列 这段DNA碱基序列来自能合成正常功能蛋白质的健康基因 发生点突变的DNA序列 DNA序列仅仅一个改变就可能产生巨大影响 它可能会让基因无法合成蛋白质，或是让基因合成出无法在体内正常工作的蛋白质 如果突变被复制到卵子或精子中，就会在家族中遗传 癌症 癌症是一种由DNA突变引发的基因遗传病 不过，只有携带致癌突变的细胞形成精子或卵子时，癌症才会在家族中遗传，这种情况十分少见 突变的诱因 除了DNA复制出错，进入细胞的能量也可能引发突变 皮肤细胞接触强烈阳光，可能会引发突变 不受控生长 突变会让细胞分裂失控，在同一个位置产生过多细胞 这些多余的细胞会团成块，叫做肿瘤 侵袭 癌变肿瘤会侵入其他组织，扩散到全身各处 它们会打乱身体正常运作，让你病得很重 白细胞 白细胞是我们免疫系统的一部分，它们就像士兵一样，搜寻并攻击包括癌细胞在内的异己细胞 癌细胞 有些癌细胞可以躲避开白细胞 不过，新型抗癌药物可以增强免疫力，帮助身体发现并对抗癌症 镰状细胞贫血 如果携带两份致病镰状细胞突变，会让红细胞改变形状，堵塞血管（也就是你身体里运输血液的管道） 不过，如果只携带一份突变基因加一份正常基因，就能帮你抵御疟疾！