EEVVOOLLUUTTIIOONN AANNDD GGEENNEETTIICCSS BBrriittaannnniiccaa IIlllluussttrraatteedd SScciieennccee LLiibbrraarryy Encyclopædia Britannica, Inc. Chicago ■ London ■ New Delhi ■ Paris ■ Seoul ■ Sydney ■ Taipei ■ Tokyo BBrriittaannnniiccaa IIlllluussttrraatteedd SScciieennccee LLiibbrraarryy © 2009 Editorial Sol 90 All rights reserved. Idea and Concept of This Work: Editorial Sol 90 Project Management: Fabián Cassan Photo Credits: Corbis, ESA, Getty Images, Micheal Simpson/Getty Images, Graphic News, NASA, National Geographic, Science Photo Library Illustrators: GuidoArroyo,PabloAschei,CarlosFranciscoBulzomi, GustavoJ.Caironi,HernánCañellas,LeonardoCésar,JoséLuis Corsetti,VaninaFarías,ManriqueFernándezBuente,JoanaGarrido, CelinaHilbert,Inkspot,JorgeIvanovich,IvánLonguini,IsidroLópez, DiegoMartín,JorgeMartínez,MarcoMenco,MarceloMorán,Alade Mosca,DiegoMourelos,LauraMourelos,PabloPalastro,Eduardo Pérez,JavierPérez,ArielPiroyansky,FernandoRamallo,ArielRoldán, MarcelSocías,NéstorTaylor,TrebolAnimation,JuanVenegas, ConstanzaVicco,CoraliaVignau,GustavoYamin,3DN,3DOMstudio Composition and Pre-press Services: Editorial Sol 90 Translation Services and Index: Publication Services, Inc. Portions © 2009 Encyclopædia Britannica, Inc. Encyclopædia Britannica, Britannica, and the thistle logo are registered trademarks of Encyclopædia Britannica, Inc. Britannica Illustrated Science Library Staff Encyclopædia Britannica, Inc. Editorial Jacob E. Safra, Chairman of the Board Michael Levy, Executive Editor, Core Editorial John Rafferty, Associate Editor, Earth Sciences Jorge Aguilar-Cauz, President William L. Hosch, Associate Editor, Mathematics and Computers Michael Ross, Senior Vice President, Corporate Development Kara Rogers, Associate Editor, Life Sciences Rob Curley, Senior Editor, Science and Technology Dale H. Hoiberg, Senior Vice President and Editor David Hayes, Special Projects Editor Marsha Mackenzie, Director of Production Art and Composition Steven N. Kapusta, Director Carol A. Gaines, Composition Supervisor Christine McCabe, Senior Illustrator International Standard Book Number (set): 978-1-59339-860-6 Media Acquisition International Standard Book Number (volume): Kathy Nakamura, Manager 978-1-59339-865-1 Britannica Illustrated Science Library: Copy Department Evolution and Genetics 2009 Sylvia Wallace, Director Julian Ronning, Supervisor Printed in China Information Management and Retrieval Sheila Vasich, Information Architect Production Control Marilyn L. Barton Manufacturing Kim Gerber, Director www.britannica.com Evolution and Genetics Contents PHOTOGRAPH ON PAGE 1 In vitro fertilization. The image shows the moment at which the sperm DNA is injected into an ovule. Myths and Scientific Evidence Page 6 Origin of Life Page 18 Human Evolution Page 38 Mechanisms of Heredity Page 54 The Age of Genetics Page 68 Yesterday, of the answers that people have found beforehand what diseases a person could throughout history, through their successes, develop will be extremely valuable in the Today, and failures, and new questions. These new field of health, because we will be able to questions have served to shape the world in choose examinations and treatments which we live, a world whose scientific, according to individual needs. Another very Tomorrow technological, artistic, and industrial promising area of medical research involves development surprises and at times the use of stem cells that have the unique FACES OF THE PAST frightens us. History is full of leaps. For capacity to be used at some future date to The skull of Australopithecus (below) thousands of years nothing may happen, regenerate organs or damaged tissues. shows a reduced cerebral portion and a strong jaw. To the right, Cro-Magnon, a W until all of a sudden some new turn or Do not wait any longer. Turn the page and hen did humans appear? What is it representative of modern humans, discovery gives an impulse to humankind. begin to enjoy this book, which may be a exhibits a more evolved skull with that makes us different from the greater cerebral capacity. For example, with the domestication of point of departure in your own adventure rest of the animals? In what way animals and the cultivation of plants, a in learning. did language develop? Why is it so profound societal revolution occurred. This important to have deciphered the sequence period of prehistory, called the Neolithic, of the human genome? This book offers which dates to 10 million years ago, opened answers to these and many other questions the way for the development of civilization. about the mysteries and marvels of human With the possibility of obtaining food evolution. Scientists maintain that modern without moving from place to place, the first humans originated in Africa because that is villages were established and produced where they have found the oldest bones. In great demographic growth. addition, genetics has just arrived at the same conclusion, since the DNA studies T he book that you have in your have confirmed that all humans are hands explains all this in an related to the African hunter-gatherers accessible way. Here you will who lived some 150 million years ago. also find information about the latest Studying the fossils, the experts also discoveries related to the structure of found that human skulls from two DNA, the molecule of heredity, that million years ago already show the opens new areas of investigation. It development of two specific contributes to the study of clinical protuberances that in the and forensic medicine and posits present-day brain control speech, new questions about the origin of the capability that perhaps was life and where we are headed as as important for early humans as humans. The possibility of the ability to sharpen a rock or throw untangling the sequence of the a spear. Today thanks to science it is human genome is not only important in possible to affirm that the brain has trying to explain why we are here and to changed drastically in the evolutionary explore our evolutionary past, but it also course of the species, reaching a greater offers the possibility of altering our complexity in humans. This has facilitated, future. In the decades to come, the among other things, the capacity to store application of genetic therapy will allow, information and the flexibility in behavior among other things, the cure of genetic that makes a human an incredibly complex disorders caused by defective genes. In individual. The purpose of this book is to tell addition, the alternative of knowing you and show you in marvelous images many Myths and Scientific Evidence BLACK SHEEP VARIOUS BELIEFS 8-9 The black color of this EVOLUTION IS A MATTER OF TIME 10-11 specimen is a clear expression of genes, the EVOLUTIONARY PROCESSES 12-13 function of which is to TO LIVE OR DIE 14-15 determine different traits. THE CRITICAL POINT 16-17 T he evolution of species cannot elements. It represents not simply an factors such as the reversal of the places in the world as well as various be considered an isolated event unlimited number of genetic mutations Earth's magnetic field or the impact of scientific theories concerning the origin in itself but rather the result of a but also changes in the environment, large meteorites on the Earth's surface. of life and of human beings. Some of the complex and constant fluctuations in sea level, varying In this chapter, we tell you stories and curious facts and photos in these pages interaction among different contributions of nutrients, and possibly legends from some of the most remote will surprise you. 8 MYTHS AND SCIENTIFIC EVIDENCE EVOLUTION AND GENETICS 9 Various Beliefs Disobedient Judaism, Islam, and the various forms of rule over nature. The first woman, Eve, emerged from one B efore the emergence of scientific theories, most people in Christianity adhere to the book of Genesis in the of Adam's ribs. Because they disobeyed the Creator by Bible, according to which the world was created by God in eating one of the forbidden fruits, Adam and Eve were the world had their own versions of the origin of the seven days. According to this account, the first human was banished from Paradise. Condemned to work the soil and for world and of humankind expressed primarily in the form created on the sixth day “in the image and likeness” of the woman to suffer during childbirth, they had three sons, Creator. The intention was for this new creature to from whom the human race descended. of myths. Many of them have reached us through the teachings PROPORTION of different religions. In many cases, the origin of the world and Thehaed ssi zree voef atlhse EDEN THE TWO SEXES The biblical story locates the Although Genesis is somewhat of humankind relates to one or several creator gods or demigods; the importance earthly Paradise in contradictory on this point, the given to the Mesopotamia. In Paradise, all dominant version states that in other cases, there is no beginning and no end. With regard to the symbols. the living species lived, and God created Eve from one of origin of the human race (the word “human” shares the same root humans had only to take Adam's ribs while he slept. what they needed. That is what the as the Latin word humus, meaning “earth”), there is a Central Nuremberg Bible illustrates. African legend that links humans to monkeys. The Matter of Creation India is a multicultural, agricultural society where much of its thousand-year-old rituals still exist. However, its sacred texts were written at very different times, from 1,000 BC (the Rigveda) to the 16th century AD (the Puranas), and they offer different versions of the origin of humankind. One of them even tells of a primal man (Purusha) from whom gods originated and from whose body parts the different castes arose. In this culture, social classes are strongly differentiated. HUMAN SHAPES FORBIDDEN Christianity represented FRUIT the Creator and the angels According to the in human form, but biblical account, Adam BRAHMA, Judaism and Islam did not and Eve ate the fruit of THE CREATOR assign a human likeness to the Tree of Knowledge of Another version states that their God. Good and Evil. the first human emerged directly from the god Brahma, whose human image YORUBA is represented by this statue. MASK represents the two sexes. The Divine Breath HERMAPHRODITE According to more recent The story explains that God gave life to other cultures, life is also identified with the texts (from the 15th century), Africa: How Monkeys Became Human inert matter through either breath, as breath of the creator of the world. In Egyptian the first person Brahma shown in the image above, or touch, as shown in mythology, for example, the breath of the god Ra, chree wataesd aw haesr mcaallpehdr oMdaitneu. ,T ahned In Africa, the continent that is today believed to be the cradle of the human this fragment of the Final Judgment, painted on “The Limitless God,” transforms into air (Shu), story goes that as a result of species, there are several myths that account for the origin of mankind. One of a chapel ceiling in the Vatican in 1541. In many which is the indispensable element of life. his dual sexual condition, he these actually interweaves it with the origin of the monkey. It tells how the creator god had a number of children, Muluku made two holes in the Earth from where the first woman and the first man both males and females. sprouted and how he taught them the art of agriculture, but they neglected it and the CREATION The work of Michelangelo Earth dried up. As punishment, Muluku banished them to the rainforest and gave them is found in the Sistine monkey tails, and he removed the tails from monkeys and ordered them to be “human.” Chapel in the Vatican. 10 MYTHS AND SCIENTIFIC EVIDENCE EVOLUTION AND GENETICS 11 Evolution Is a 150 million 1 Dinosaurs Matter of Time Animals that lived years millions of years ago left behind their fossil remains. 2 Sediment is the typical age of dinosaur fossils. T Sediment from rivers and seas oward the 18th century, scientific progress is deposited over the skeleton and forms into layers. demanded a different explanation of the myth of the origin of the world and of life. Even before 3 Burial Darwin, the work of naturalists and the discovery of Bacteria and other fossils pointed to the fact that time, measured not in underground organisms can modify the buried skeleton. years but in millennia, runs its course, allowing each species to become what it is. Genetic mutations occur through the generations, and interaction with the environment determines that the most suitable traits will 4 Discovery be transmitted (natural selection) and that a population Erosion on the Earth's will evolve in relationship to its ancestors. The idea is not surface leads to the related to “improvement” but rather to change as the discovery of fossil remains from millions of years ago. origin of diversity, to the ramifications of evolutionary lines tracked through paleontological or genetic studies. A Common History A Animals that look very different may be and two pairs of limbs connected to it. This built according to the same basic body suggests that they all share a common design. For example, dogs, whales, and ancestor. In mammals, the bones of the Fossil Remains human beings are mammals. All have the limbs are the same even if they are same skeletal design with a spinal column morphologically different from one another. The evidence of past life is registered in fossils, preserved between layers of sedimentary rocks deposited one on top of KEY another through geological eras. An analysis Humerus Ulna Radius Carpal Metacarpal of fossils helps determine their age. Through studies of fossil populations, it is possible to learn about the structure of old communities, In mammals, the basic design of the reason given species became the limb is very similar—an upper extinct, and how animals and bone (humerus), followed by a plants evolved over time. pair of lower ones (radius and ulna), and then the carpals and metacarpals with up to five digits. PETRIFIED FOSSILS This head of an Albertosaurusdiscovered as a fossil can be studied using geological or biomolecular analyses. B Only one fossil is Genetics HUMAN found for every 20,000 With the use of advanced biomolecular techniques, it is possible to examine the evolutionary legacy of a CAT species and figure out when evolutionary lines extinct diverged. Many anthropologists use mitochondrial DNA (which is inherited from the mother) to species. reconstruct human evolution. This type of analysis is BAT WHALE also used to reconstruct the family trees of animals. 12 MYTHS AND SCIENTIFIC EVIDENCE EVOLUTION AND GENETICS 13 Evolutionary Processes B DREPANA FALCATARIA I was found hidden on a tree n addition to natural selection, the famous theory developed by in Norfolk (U.K.) in 1994. Charles Darwin in the 19th century, there are other evolutionary Mutation processes at work at the microevolutionary scale, such as involves the modification of the sequences mutations, genetic flow (i.e., migration), and genetic drift. However, of genetic material found in DNA. When a cell divides, it produces a copy of its DNA; for evolutionary processes to take place, there must be genetic however, this copy is sometimes imperfect. variation—i.e., modifications to the proportion of certain genes This change can occur spontaneously, such as from an error in DNA replication (alleles) within a given population over time. These genetic (meiosis) or through exposure to radiation differences can be passed on to subsequent generations, or chemical substances. thereby perpetuating the evolutionary process. THE PROCESS A mutation is a discrepancy in the DNA copy. A Natural Selection This is one of the basic mechanisms of evolution. It is the process of species survival and adaptation to changes in the environment, and it involves shedding some traits and strengthening others. This revolutionary transformation COPY WITH CORRECT takes place when individuals with certain traits have a MUTATION COPY survival or reproduction rate higher than that of other individuals within the same population, thus passing along these genetic traits to their descendants. C GENETIC VARIATION IN THE GIRAFFE Genetic Flow 1 The transfer of genes from one population to another occurs particularly when two COMPETITION populations share alleles (different versions In the 19th century, because of genes). For example, when a population of the theories of Darwin and of brown beetles mixes with a population Lamarck, among others, it of green beetles, there might be a higher was believed that the frequency of brown beetle genes in the ancestors of giraffes had green beetles. This also occurs when new short necks. 3 alleles combine as a result of mixing, as SURVIVAL when Europeans mixed with Native The population of moths Americans. with black alleles grows and 2 surpasses the population MUTATION with gray alleles. D On the basis of spontaneous mutations, some individuals developed Genetic Drift longer necks, allowing them to survive in the A gradual change in the genetic makeup of a THE GEOMETRIC MOTH competition for food. population that is not linked to the AND ITS ENVIRONMENT environment. Unlike natural selection, this is The genes of geometric moths, which live a random process that does not generate on tree bark lichen, have different adaptations. Genetic drift is present in small 3 versions (alleles) for gray and black. At 95% populations in which each individual carries 1 2 ADAPTATION the start of the Industrial Revolution in within itself a large portion of the genetic Their long necks England, the gray moth was better able to MIMESIS POLLUTION pool, especially when a new colony is allowed them to camouflage itself than the black moth and The population of moths Moths with black alleles find established (the founding effect), or when a survive and pass thus better able to avoid predators. All with gray alleles grows themselves better adapted to THE PROPORTION OF high number of individuals die and the along this trait to this changed with the emergence of larger because of its their new environment, which is BLACK MOTHS FOUND IN population rebuilds from a smaller genetic their descendants. pollution, which blackened tree trunks. camouflage. the result of industrial pollution. URBAN AREAS pool than before (the bottleneck effect).