CHANGES OVER TIME The Evolution of Animal Traits Chapters 15 and 16 EVOLUTION The theory of evolution can explain the diversity of life on Earth. Evolution, otherwise known as change over time, is the process by which modern organisms have descended from ancient organisms. Mimicry Type of evolution when one organism comes to resemble, or mimic, another organism over time. Viceroy Monarch Convergent Evolution Convergent evolution occurs when 2 groups of unrelated species adapt to the same kind of environment. Example: sharks (fish-like), dolphins (mammals) Theories of Evolution Many important theories about animals and animal adaptations were developed hundreds of years ago. We will discuss a few of these and the scientists/professionals that developed them, like Darwin, Lamarck and Malthus. Charles Darwin Charles Darwin contributed more than any other scientist to our current understanding of evolution. He gave us the Theory of Natural Selection. Charles Darwin On many trips abroad, Darwin observed a tremendous diversity of organisms and noticed that many plants and animals were very well suited to their environment. Charles Darwin On the Galapagos Islands, he noted that though the islands were close together, they had very different climates and thus the physical appearance of similar organisms (like birds) varied from island to island. Darwin’s finches Charles Darwin Darwin collected many fossils from ancient organisms and wondered why the species represented by the fossils no longer existed. Knowing that the Earth could change over time, Darwin realized that life might as well. Jean Baptiste Lamarck French scientist who was one of the first scientists to recognize that evolution had occurred and that organisms had to adapt to their environment in order to survive He said that body changes that an organism develops over time could be passed on to their offspring Ex. Giraffes developed long necks to reach food Jean Baptiste Lamarck Lamarck hypothesized that an organism could gain or lose traits during its lifetime by using or not using organs These changes could be passed on to their offspring and eventually change the whole species over time. Thomas Malthus Malthus was an economist that hypothesized that if a population continued to grow unchecked, it would run out of living space and food. NATURAL SELECTION Darwin’s Theory of Natural Selection states that individuals differ and that some of these differences can be passed on to their offspring. More offspring are produced than can survive & reproduce in a given area, so there is competition for limited resources like food, mates and territory. NATURAL SELECTION NATURAL SELECTION Individuals that are best suited to their environment are able to survive and reproduce (therefore passing on their genes) most successfully so that it creates a “survival of the fittest”. Fitness is the ability to survive and reproduce in a specific environment and results from making adaptations to the environment, thus causing a species to change over time. Adaptation The changing of a species that results in its being better suited to its environment and thus more successful in living and reproducing. NATURAL SELECTION Darwin argued that species alive today all descended from a common ancestor, but each made its’ own adaptations according to their environment. Darwin’s Evidence that Supports Evolution 1. FOSSILS – Scientists can compare fossils from older & younger rock layers Darwin’s Evidence that Supports Evolution 2. GEOGRAPHIC DISTRIBUTION OF LIVING SPECIES – the presence of similar but unrelated organisms in similar environments. Darwin’s Evidence that Supports Evolution 3. HOMOLOGOUS STRUCTURES – body parts that develop from the same type of embryonic tissue, but have different mature forms in different animals. They provide evidence that organisms descended from a common ancestor. Darwin’s Evidence that Supports Evolution 4. SIMILARITIES IN EARLY DEVELOPMENT – The embryonic stages of many animals are very similar, which also provides evidence that animals share common ancestors. Genetic Variation A population is defined as a group of individuals of the same species that interbreed. Members of a population share common genes called a gene pool. Genetic variation occurs when genes either mutate or are shuffled, which both increase the different genetic combinations possible within a species. Speciation Speciation is the formation of new species. For one species to evolve into two new species, the gene pools of the two populations must become reproductively isolated, which means they can no longer interbreed and produce fertile offspring. Reproductive isolation can be 1 of 3 types: Types of Speciation BEHAVIORAL ISOLATION: Occurs when populations have different courtship rituals. GEOGRAPHIC ISOLATION: Occurs when populations get separated by physical barriers such as mountains or rivers. (Ex. Grand Canyon) TEMPORAL ISOLATION: Occurs when populations reproduce at different times of the year. (Ex. Different breeding times in animals or different times when flowers bloom.) History of Life The first known life forms evolved about 3.5 billion years ago & resemble modernday bacteria. The first eukaryotes evolved about 2 billion years ago. FOSSILS Fossils tell us a great deal about the past. They are essentially preserved traces (like footprints or burrows) or remains (like bone, teeth and shells) of ancient life that once existed on Earth. FOSSILS We can use fossils to infer what life on Earth used to be like once upon a time. Scientists often use dating methods to determine the age of fossils. FOSSILS Radioactive elements in fossils decay at a steady rate over time, which is known as halflife. A half-life is the length of time needed for half of the radioactive atoms in a fossil to decay. By finding this, we can determine the full age of a fossil. EVOLUTION Remember, an organism’s ability to survive and reproduce makes it successful, which happens only if it can adapt to its’ environment, eventually leading to an overall change (evolution) in the species over time. In other words, if it doesn’t change it won’t survive!! You’ll be quizzed over these notes next class!