Charles Darwin, Evolution of Species, and Natural Selection

Natural Selection Individuals with favorable traits are more likely to leave more offspring better suited for their environment. Example: English peppered moth (Biston betularia) - light and dark phases

Artificial Selection The selective breeding of domesticated plants and animals by humans. Question: What’s the ancestor of the domesticated dog? Answer: WOLF

Species Individuals have the potential to interbreed and produce viable or fertile offspring. A localized group of individuals belonging to the same species.

Gene Pool The total collection of genes in a population at any one time.

Four Mechanisms of Natural Selection (things that cause evolution) 1. Genetic drift: Change in the gene pool of a small population due to chance. Two examples: a. Bottleneck effect- drastic reduction in population size b. Founder effect- resulting from the colonization of a new location by a small number of individuals.

Four Mechanisms of Natural Selection 2. Gene Flow: The gain or loss of alleles from a population by the movement of individuals or gametes. Immigration or emigration. 3. Mutation: Change in an organism’s DNA that creates a new allele. 4. Non-random mating: The selection of mates other than by chance.

Speciation The evolution or formation of new species.

Spontaneous Generation or Abiogenesis The idea that life could arise from non-living matter People used to think that beetles came from dung and maggots came from meat left standing in the open for days Today, we know that this is not true

Evolution It is defined by the simple phrase “change over time.” It’s a process by which modern organisms have descended from ancient organisms There are many scientists included in the evolutionary discussion, but none more so than Charles Darwin.

Charles Darwin His observations led to a revolutionary theory about the way life changes over time. An English scientist In 1831, he set sail on the H.M.S. Beagle around the world. Darwin conducted a large amount of his studies on the Galapagos Islands.

Galapagos Darwin noticed differences between the beaks of finches and the shells of tortoises in the different islands of the Galapagos. He notes that what once was one species had evolved into different species suited to live in their specific environment

Finches As you can see, the finches, over time, developed a beak that best suit their survival on each particular island of the Galapogos.

The Origin of Species Was a book that Darwin published that shocked the world and everything it knew about life, especially from a religious standpoint.

Mass Extinction Mass extinction - when many types of living things become extinct at the same time Extinct - the species died out At the end of the Paleozoic Era, a mass extinction affected both plants & animals on land & in the sea 95% of life in the oceans disappeared

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

Patterns of Evolution Extinction: More than 99% of all species are now extinct It usually happens for a reason; species compete for resources, & environments change Some species adapt & survive, others become extinct

Patterns of Evolution Adaptive radiation - when a single species has evolved, through NS, into diverse forms that live in different ways Ex.) Darwin’s Finches

Patterns of Evolution Punctuated equilibrium - a pattern of long, stable periods interrupted by brief periods of more rapid change

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

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

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

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 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 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