Fundamentals of Biology - Evolution Lecture PDF

The Cell Fundamentals of Biology Evolution Dr. Madiha Saeed Assistant Professor Interdisciplinary Research Center in Biomedical Materials (IRCBM), COMSATS...

The Cell Fundamentals of Biology Evolution Dr. Madiha Saeed Assistant Professor Interdisciplinary Research Center in Biomedical Materials (IRCBM), COMSATS University Islamabad, Lahore Campus © Copyright Evolution  The process of change over time that has resulted in the astounding array of organisms found on Earth.  An understanding of evolution helps us to make sense of everything we know about life on Earth.  As the fossil record clearly shows, life has been evolving for billions of years, resulting in a vast diversity of past and present organisms.  But along with the diversity there is also unity.  For example, while sea horses, jackrabbits, hummingbirds, crocodiles, and giraffes all look very different, their skeletons are organized in the same basic way. © Copyright 2 Evolution  The scientific explanation for the unity and diversity of organisms is evolution: a process of biological change in which species accumulate differences from their ancestors as they adapt to different environments over time.  Thus, we can account for differences between two species (diversity) with the idea that certain heritable changes occurred after the two species diverged from their common ancestor.  However, although these two species differ in some ways, they also share certain traits (unity) simply because they have descended from a common ancestor. © Copyright 3 Classifying the Diversity of Life  Diversity is a hallmark of life. Biologists have identified and named about 1.8 million species of organisms, and estimates of the number of living species range from about 10 million to over 100 million.  These remarkably diverse forms of life arose by evolutionary processes.  How biologists organize the enormous variety of life-forms on this planet into manageable and informative groupings.  Humans have a tendency to group diverse items according to their similarities and relationships to each other.  Consequently, biologists have long used careful comparisons of form and function to classify life-forms into a hierarchy of increasingly inclusive groups. © Copyright 4 Classifying the Diversity of Life  Consider, for example, the species known as the leopard (Panthera pardus).  Leopards belong to the same genus (Panthera) as tigers and lions.  In the last few decades, new methods of assessing species relationships, such as comparisons of DNA sequences, have led to a reevaluation of the larger groupings.  Although this reevaluation is ongoing, biologists currently place all of the kingdoms of life into three higher levels of classification called domains: Bacteria, Archaea, and Eukarya (Figure 1.12). © Copyright 5 Classifying the Diversity of Life © Copyright 6 Classifying the Diversity of Life  Two of the three domains—Bacteria and Archaea— consist of single- celled, prokaryotic organisms.  All the eukaryotes (organisms with eukaryotic cells) are grouped in domain Eukarya.  This domain includes three kingdoms of multicellular eukaryotes: Plantae, Fungi, and Animalia.  These three kingdoms are distinguished partly by their modes of nutrition.  Plants produce their own sugars and other food molecules by photosynthesis. © Copyright 7 Classifying the Diversity of Life  Fungi absorb dissolved nutrients from their surroundings.  Animals obtain food by eating and digesting other organisms.  Animalia is, of course, the kingdom to which we belong.  The most numerous and diverse eukaryotes are the mostly single-celled protists. © Copyright 8 Unity in the Diversity of Life  Although diversity is apparent in the many forms of life, there is also remarkable unity.  Consider, for example, the similar skeletons of different animals and the universal genetic language of DNA (the genetic code).  In fact, similarities between organisms are evident at all levels of the biological hierarchy.  The history of life, as documented by fossils and other evidence, is an ever-changing Earth billions of years old, inhabited by an evolving cast of living forms (Figure) © Copyright 9 Unity in the Diversity of Life © Copyright 10 Charles Darwin and the Theory of Natural Selection An evolutionary view of life came into sharp focus in 1859, when Charles Darwin published one of the most important and influential books ever written, On the Origin of Species by Means of Natural Selection (Figure). © Copyright 11 Charles Darwin and the Theory of Natural Selection His three essential observations were the following:  First, individuals in a population vary in their traits, many of which seem to be heritable (passed on from parents to offspring).  Second, a population can produce far more offspring than can survive to produce offspring of their own. Competition is thus inevitable.  Third, species generally are suited to their environments—in other words, they are adapted to their circumstances. © Copyright 12 Charles Darwin and the Theory of Natural Selection  For instance, a common adaptation among birds that eat hard seeds is an especially strong beak.  By making inferences from these three observations, Darwin developed a scientific explanation for how evolution occurs.  He reasoned that individuals with inherited traits that are better suited to the local environment are more likely to survive and reproduce than are less well-suited individuals.  Over many generations, a higher and higher proportion of individuals in a population will have the advantageous traits. © Copyright 13 Charles Darwin and the Theory of Natural Selection  Darwin called this mechanism of evolutionary adaptation natural selection because the natural environment consistently “selects” for the propagation of certain traits among naturally occurring variant traits in the population (Figure). © Copyright 14  Darwin’s Focus on Adaptation  During the voyage of the Beagle, Darwin observed many examples of adaptations, inherited characteristics of organisms that enhance their survival and reproduction in specific environments.  Later, as he reassessed his observations, he began to perceive adaptation to the environment and the origin of new species as closely related processes.  Could a new species arise from an ancestral form by the gradual accumulation of adaptations to a different environment? © Copyright 15 Darwin’s Focus on Adaptation © Copyright 16  Darwin’s Focus on Adaptation  From studies made years after Darwin’s voyage, biologists have concluded that this is indeed what happened to a diverse group of finches found on the Galápagos Islands  The finches’ various beaks and behaviors are adapted to the specific foods available on their home islands (Figure 19.6).  Darwin realized that explaining such adaptations was essential to understanding evolution.  His explanation of how adaptations arise centered on natural selection, a process in which individuals that have certain inherited traits tend to survive and reproduce at higher rates than do other individuals because of those traits. © Copyright 17