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

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.

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.

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.

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.

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!