Ch. 15 Darwin’s Theory of Evolution Unit 5 Evolution Ch. 15 Darwin’s Theory of Evolution

The Puzzle of Life’s Diversity Evolution - modern organisms have descended from ancient organisms (change over time) Theory - a well-supported, testable explanation of phenomena that have occurred in the natural world

Voyage of the Beagle Charles Darwin contributed most to our understanding of evolution He made observations & collected evidence that led him to propose a hypothesis about the way life changes over time

Voyage of the Beagle That hypothesis, now supported by a large amount of evidence, has become the theory of evolution

Darwin’s Observations Darwin collected the preserved remains of ancient organisms - Fossils Some of these fossils resembled organisms that were still alive Others looked unlike any creature ever seen

Darwin’s Observations The Galapagos Islands influenced Darwin the most He observed that the characteristics of animals & plants varied among the different Islands

An Ancient, Changing Earth Hutton & Lyell helped scientists recognize that Earth is millions of years old They also noted that the processes that changed Earth in the past are the same processes that are changing Earth now

Lamarck’s Evolution Hypothesis The year that Darwin was born, Lamarck published his hypothesis He proposed that by selective use or disuse of organs, organisms acquired or lost certain traits during their lifetime Over time, this process led to change in a species

Lamarck’s Explanation

Population Growth English economist, Malthus, published a book, noting that babies were being born faster than people were dying He stated that if the human population continued to grow unchecked, sooner or later there would be insufficient living space & food for everyone

Darwin Presents His Case Darwin published the results of his work in a book, On the Origin of Species In his book, he proposed a mechanism for evolution called natural selection He stated that evolution has been taking place for millions of years, & continues in all living things

Inherited Variation & Artificial Selection Artificial selection - nature provided the variation, & humans selected those variations that they found useful It has produced diverse plants & animals by selectively breeding for different traits

Evolution by Natural Selection Struggle for existence - the members of each species compete regularly to obtain food, living space, & other necessities of life Predators that are faster & better at catching prey are more likely to survive

Evolution by Natural Selection Fitness - the ability of the organism to survive & reproduce in its specific environ. Fitness is the result of adaptations

Evolution by Natural Selection Adaptation - any inherited characteristic that increases an organisms’ chance of survival Successful adaptations allow organisms to become better suited to their environ. & thus better able to survive

Evolution by Natural Selection Individuals that are better suited to their environ., with adaptations that enable fitness, survive & reproduce most successfully - Survival of the Fittest

Evolution by Natural Selection Since it is similar to artificial selection, Darwin referred to survival of the fittest as - Natural Selection In both AS & NS, only certain individuals of a population produce new individuals

Evolution by Natural Selection However, in NS, the traits being selected, & therefore, increasing over time, contribute to an organism’s fitness NS takes place without human control or direction

Evolution by Natural Selection NS results in changes in the inherited characteristics of a population, that increase a species’ fitness in its environ. Over time, NS produces organisms that have different structures, & occupy different habitats

Evolution by Natural Selection As a result, species today look different from their ancestors Each living species has descended, with changes, from other species over time - Descent with Modification

Evolution by Natural Selection Descent with modification also implies that all living organisms are related to each other Common descent - all species (living & extinct) were derived from common ancestors

Evidence of Evolution Darwin argued that living things have been evolving on Earth for millions of years Evidence of this could be found: in the fossil record, the geographical distribution of living species, homologous structures of living organisms, & similarities in early development

Evidence of Evolution The Fossil Record: Darwin noticed that the sizes, shapes, & varieties of related organisms preserved in the fossil record, changed over time

Evidence of Evolution Geographic Distribution of Living Species: Darwin realized that similar animals in different locations were the product of different lines of evolutionary descent

Evidence of Evolution Homologous Body Structures: Homologous structures - structures that have different mature forms but develop from the same embryonic tissues Not all homologous structures serve important functions Organs of many animals are so reduced in size that they are just vestiges, or traces, of homologous organs

Homologous Structures

Evidence of Evolution Homologous Body Structures: Vestigial organs - may resemble miniature legs, tails, or other structures, a trace of a homologous structure

Evidence of Evolution Similarities in Early Development: The early stages or embryos, of many animals with backbones are very similar

Summary of Darwin’s Theory Individual organisms differ, & some of this variation is heritable Organisms produce more offspring than can survive, & many that do survive do not reproduce

Summary of Darwin’s Theory Because more organisms are produced than can survive, they compete for limited resources Individuals best suited to their environ., survive & reproduce most successfully

Summary of Darwin’s Theory These organisms pass their heritable traits to their offspring This process of NS causes species to change over time

Summary of Darwin’s Theory Species alive today are descended with modification from ancestral species that lived in the distant past This process, where diverse species evolved from common ancestors, unites all organisms on Earth into a single tree of life