Transcript Slide 1
Chapter 15 Important People • James Hutton and Charles Lyell – geologists who helped scientists recognize that Earth is many millions of years old, and that the processes that changed Earth in the past are the same processes that operate in the present. • Jean-Baptiste Lamarck – recognized that living things have changed over time and that all species were descended from other species. He proposed that by selective use or disuse of organs, organisms acquired or lost certain traits during their lifetime. – Theses traits could be passed off to offspring and lead to change in a species. – We now know that part of his hypothesis was incorrect. • Thomas Malthus – economist who reasoned that if the human population continued to grow unchecked, sooner or later there would not be enough living space and food for everyone. – He said that the only factors working against this growth were war, famine, and disease. • Charles Darwin – (duh!!!) 25 years after his trip, he published On the Origin of Species because another naturalist, Alfred Russel Wallace was about to publish the same idea! – The book came out in 1859 and natural selection was presented as the mechanism for evolution. Evolution • The central ideas of evolution are that life has a history — it has changed over time — and that different species share common ancestors. Darwin’s Ideas • Struggle for existence – Members of each species compete regularly to obtain food, living space, and other necessities of life. • Ex: Predators who are faster will catch more prey, but prey that are faster, better camouflaged, or better protected can avoid being caught. • Fitness – The ability of an individual to survive and reproduce in its specific environment. – Fitness is the result of ADAPTATION. • Adaptation – An inherited feature that is common in a population because it provides some improved function and increases survival. – Adaptations can take many forms: a behavior that allows better evasion of predators, a protein that functions better at body temperature, or an anatomical feature that allows the organism to access a valuable new resource — all of these might be adaptations. • Natural Selection (“Survival of the Fittest”) – Individuals that are better suited for their environment , with adaptations that enable fitness, survive and reproduce most successfully. • Individuals with characteristics that are not well suite for their environment , with low levels of fitness, either die or leave few offspring. – Over time, natural selection results in changes in the inherited characteristics of a population. – These changes increase a species’ fitness in its environment. – Natural selection takes place without human control or direction. • If humans controlled it, this would be called artificial selection. • Descent with Modification – Over long periods, natural selection produces organisms that have different structures, establish different niches, or occupy different habitats. – This is why species today look different from their ancestors. – COMMON DESCENT: All species, living and extinct, were derived from common ancestors. • “Tree of Life” links all living things. Evidence of Evolution 1. 2. 3. 4. 5. 6. Fossil record Geographic Distribution Homologous Structures Vestigial Organs Embryology DNA Fossil Record • Darwin saw fossils as a record of the history of life on Earth. • By comparing fossils from older rock layers with fossils from younger rock layers, scientists could document the fact that life on Earth has changed over time. Geographic Distribution • Species now living on different continents had each descended from different ancestors. • However, because some animals on each continent were living under similar ecological conditions, they were exposed to similar pressures of natural selection. • Because of these similar selection pressures, different animals ended up evolving certain features in common. SEE PAGE 383 Homologous Structures • We use homologous characters — characters in different organisms that are similar because they were inherited from a common ancestor that also had that character. – An example of homologous characters is the four limbs of tetrapods. • Birds, bats, mice, and crocodiles all have four limbs. Sharks and bony fish do not. – The ancestor of tetrapods evolved four limbs, and its descendents have inherited that feature — so the presence of four limbs is a homology. • Not all characters are homologies. – For example, birds and bats both have wings, while mice and crocodiles do not. Does that mean that birds and bats are more closely related to one another than to mice and crocodiles? No. When we examine bird wings and bat wings closely, we see that there are some major differences. • Bat wings consist of flaps of skin stretched between the bones of the fingers and arm. • Bird wings consist of feathers extending all along the arm. – These structural differences suggest that bird wings and bat wings were not inherited from a common ancestor with wings. – Bird and bat wings are analogous — that is, they have separate evolutionary origins, but look similar because they evolved to serve the same function. Vestigial Organs • A vestigial structure is a feature that was an adaptation for the organism's ancestor, but that evolved to be non-functional because the organism's environment changed. – Fish species that live in completely dark caves have vestigial, non-functional eyes. – When their sighted ancestors ended up living in caves, there was no longer any natural selection that maintained the function of the fishes' eyes. – So, fish with better sight no longer out-competed fish with worse sight. – Today, these fish still have eyes — but they are not functional and are not an adaptation; they are just the by-products of the fishes' evolutionary history. Embryology • The early stages, or embryos, of many animal with backbones are very similar. • The same groups of embryonic cells develop in the same order and in similar patterns to produce the tissues and organs of all vertebrates. – This is how homologous structures are produced. DNA Evidence • Similar species share similar genetics like genes and proteins. • The fact that organisms have evolved successively from relatively simple ancestors implies that a record of evolutionary change is present in the cells of each of us, in our DNA. – When an ancestral species gives rise to two or more descendants, those descendants will initially have fairly high overall similarity in their DNA. However, as the descendants evolve independently, they will accumulate more and more differences in their DNA. • Comparison of the DNA of different species provides strong evidence for evolution. Species deduced from the fossil record to be closely related are more similar in their DNA than are species thought to be more distantly related.