Evolution

1. Evolution Descent with Modification/ Change over Time

2. Change over time • Evolution – theory that concerns how species change over time. • the process by which modern organisms have descended from ancient organisms. • change is very slow and only in minor ways • Can individual organisms evolve? NO!!! • Populations of organisms do evolve as a result of a change in gene pool. • Theory – a well supported, testable explanation of phenomena that have occurred in the natural world. • Charles Darwin –joined the crew of the HMS Beagle and set sail for a voyage around the world. During his travels, Darwin collected evidence that led him to propose the theory of evolution.

3. Darwin’s theory of evolution • Galapagos Islands – Darwin observed that the characteristics of many animals and plants varied noticeably among the different islands of the Galapagos.

4. Lamarck’s evolution hypothesis • Jean-Baptiste Lamarck – proposed that by selective useor disuse of organs, organisms acquiredor lost certain traits during their lifetime. • Use and disuse of organs – organisms develop new organs or change the structure and function of old organs. • Continual use of an organ would result in the acquired trait for a new organ. • Disuse would result in the disappearance of an organ because it was no longer needed. • Inheritance of acquired traits – believed that offspring would inherit useful structures developed by parents. • Lamarck’s hypothesis is now known to be incorrect. While organisms do adapt to their environment, an individual’s genetic makeup cannot change. • Only genetic variations are passed on from generation to generation. • In other words, the discovery of genes proved Lamarck’s hypothesis invalid.

5. Darwin presents his case • On the Origin of Species – Darwin’s book, published in 1859. • Here he poses a mechanism for evolution that he called natural selection.

6. Evolution by natural selection • Struggle for Existence – members of each species compete to obtain food, living space, and other necessities for life. • Fitness – the ability of an individual to survive and reproduce in its specific environment. • Adaptation – any inherited characteristic that increases an organism’s chance for survival; gives an organism an advantage in its particular environment. • Successful adaptations enable organisms to become better suited to their environment and thus better able to survive and reproduce.

7. Evolution by natural selection • Survival of the Fittest – individuals that are better suited to their environment and have adaptations that enable fitness, survive and reproduce most successfully. Thus, passing the genes that allow them to be better suited on to their offspring. Individuals with characteristics that are not well suited to their environment have low levels of fitness, and either die or leave few offspring. • Darwin referred to this as natural selection. • Over time, natural selection results in changes in the inherited characteristics of a population. These changes increase a species’ fitness in its environment.

8. Descent with modification • Descent with Modification – over time, natural selection produces organisms that have different structures and establish different niches. As a result, species today look different from their ancestors. • Common Descent – all species – living and extinct – are derived from common ancestors, therefore a single “tree of life” links all living things.

9. Summary of darwin’s theory • Variation exists within a species. • Organisms produce more offspring than can survive. • All organisms compete for limited natural resources (food, water, shelter). • Each unique species has different advantages and disadvantages in the struggle for existence. • The environment selects organisms with beneficial traits. • Natural selection – individuals with adaptive traits have a greater chance than others to survive and pass on the genes for these beneficial traits to their offspring.

10. Evidence of evolution • The fossil record • Geographic distribution of living species • Similarities in embryology/early development • Similarities in anatomical (body) structures • Biochemical analysis • Ice core drillings

11. The fossil record • This stratigraphic column shows the order in which organisms appeared. Each layer represents a particular time frame and shows an organism which was found during that time. • The oldest fossils appear in lower layers, and the most recent fossils at the top. This allows for placement of fossils to be used as an aid in dating the organism found.

12. Geographic distribution • Armadillos and anteaters descended from a common ancestor, yet on different continents?

13. Geologic processes • Tectonic plates have drifted atop Earth’s mantle • Locations of continents and ocean basins influence Earth’s climate • Species move, adapt to new environments

14. embryology

15. Anatomical evidence • The more closely related a species, the more similar their structures will be. • Homologous structures – body parts with structures that are very similar, even though they have entirely different functions. Ex. Bones in a whale’s flipper, a human’s arm or bat’s wing • Vestigial structures – body parts that have degenerated or reduced in size and seem to serve no function. Ex. Tail-bone, wisdom teeth, appendix Boas and whales – small hip and leg bones (pelvic girdle) • Analogous structures – body parts that have the same function but are NOT similar in structure. Ex. Wing of a bird and wing of a butterfly

16. Homologous structures

17. Vestigial structures Vestigial organs associated with eye structures Vestigial remains of a pelvic girdle in a whale

18. Analogous structures • Analogous structures are a contrast to homologous structures. • These structures are of no use in classifying organisms or in working out their evolutionary relationships with each other.

19. Biochemical analysis • Biochemical analysis – study of chemicals (DNA, cells, proteins, blood, enzymes) that are within organisms. • Nutall precipitation technique – used to test similarities of blood proteins, particularly antibodies. • The stronger the agglutination, the more closely related the organisms. • Species - a group of similar organisms that share a common ancestor. • species do not reproduce outside the group and produce fertile offspring.

20. Genes and variation • Changes in genes produce heritable variation on which natural selection can operate. • Gene pool – consists of all genes, including all the different alleles that are present in a population. • Relative Frequency – the number of times an allele occurs in a gene pool, compared with the number of times other alleles for the same gene occur. • Typically expressed as a percentage • Has nothing to do with dominant/recessive • In genetic terms, evolution is any change in the relative frequency of alleles in a population.

21. Genes and variation • Inherited variation – changes in genes provided by nature. • Artificial selection – “controlled breeding” • Process controlled most directly by humans • Humans select the variations that they find useful.

22. Sources of genetic variation • Mutation – a change in DNA • Mutations are a source of new genetic material. • They add genetic material to a population’s gene pool thereby increasing variation within the population. • Mutations can be harmful, beneficial or neutral. • Causes of mutations: • Ultraviolet light • X-rays • Radioactivity • Certain chemicals (mutagens) • Random errors in DNA coding

23. Sources of genetic variation • Gene shuffling – genetic recombination (in sexual reproduction only) • The 23 pairs of chromosomes found in humans can form 8.4 million different combinations of genes – before crossing over. • Gene shuffling produces many different combinations of genes, but does not alter the relative frequencies of each type of allele in the population.

24. Single gene and polygenic traits • The number of phenotypes produced for a given trait depends on how many genes control the trait. • Single gene trait – a trait controlled by a single gene with two alleles. (ex. Widow’s peak) • Polygenic trait – trait controlled by two or more genes. Each of these genes often has two or more alleles. As a result, one polygenic trait can have many possible genotypes and phenotypes. (ex. Height in humans).

25. Natural selection on single gene traits • Populations evolve, not individual organisms. • Natural selection on single-gene traits can lead to changes in allele frequencies and thus to evolution.

26. Natural selection on polygenic traits • Directional selection – when individuals at one end of the curve have higher fitness than individuals at another end of the curve, directional selection takes place.

27. Natural selection on polygenic traits • Stabilizing selection – when individuals near the center of the curve have higher fitness than individuals at either end of the curve. • This type of selection leads to a reduction of variation in a species.

28. Natural selection on polygenic traits • Disruptive selection – when individuals at the upper and lower ends of the curve have higher fitness than individuals near the middle.

29. Genetic drift • Genetic drift – random change in allele frequencies that occurs in small populations. • Founder effect – allele frequencies change as a result of the migration if a small subgroup of a population.

30. Evolution vs. genetic equilibrium • Hardy-Weinberg Principle – allele frequencies in a population will remain constant unless on or more factors cause those frequencies to change. • Genetic equilibrium – the situation in which allele frequencies remain constant. • For evolution to occur some external factor must upset the genetic equilibrium of a population.

31. Evolution vs. genetic equilibrium • Five conditions are required to maintain genetic equilibrium: • There must be random mating. • The population must be very large. • There can be no movement into or out of the population. • There can be no mutations. • There can be no natural selection. If these conditions are not met, then genetic equilibrium will be disrupted and the population will evolve.

32. Patterns of evolution • Macroevolution – the large scale evolutionary patterns and processes that occur over long periods of time. • Extinction – • More than 99% of all species that have ever lived are now extinct. • Several times in earth’s history, mass extinctions wiped out entire ecosystems. • Each mass extinction provides opportunities for organisms that survive and often results in a burst of evolution that produces many new species.

33. Patterns of evolution • Divergent evolution – the process by which related species become less alike; evolve into a variety of species • Leads to speciation –the formation of a new species. • Ex. Polar bears diverged from brown bears • Camels and llamas • Also results in adaptive radiation – the process by which members of a species adapt to a variety of habitats. • Ex. Darwin’s (Galapagos) finches – 13 different variations • Biodiversity is believed to be the result of speciation and extinction.

34. Patterns of evolution • Adaptive radiation – when a single species or small group of species evolves into several different forms that live in different ways.

35. speciation • As new species evolve, populations become reproductively isolated from each other. • Reproductive isolation – when members of two populations cannot interbreed and produce fertile offspring.

36. Types of reproductive isolation • Behavioral isolation – occurs when two populations are capable of interbreeding but have differences in courtship rituals or other reproductive strategies that involve behavior. (ex. Birds with different mating songs). • Temporal isolation – two or more species reproduce at different times. (ex. Flowers releasing pollen at different times of the year). • Geographic isolation – two populations are separated by geographic barriers. (ex. Colorado river separates two types of squirrels).

37. Geographic isolation • The movement of tectonic plates influences evolution by changing the locations of continents, causing some species to be geographically isolated from others. • Geographic isolation can result from • Mountain ranges • Volcanic eruptions – lava flows • Rivers • Earthquakes • Deforestation • Continents • Islands

38. Testing natural selection in nature

39. Speciation in darwin’s finches • Founders arrive – finches from South American mainland (species A) populated the Galapagos. • Geographic isolation – birds from species A crossed to another Galapagos island. The two populations became isolated from one another and had different gene pools. • Changes in the gene pool – populations on the new island adapted to their environment, forming population B. • Reproductive isolation – because of their adaptations and different beaks, species A and B do not mate together if they come in contact. • Ecological competition – during dry season, individuals compete for food, and over time birds evolve better beaks (species C). • Continued evolution – this process continues over several generations and over time produces the 13 species seen today.

40. Patterns of evolution Convergent evolution – the process by which unrelated organisms develop similar characteristics; analogous structures. • occurs when different species share the same environmental surroundings • Ex. Whales and dolphins (mammals) now resemble fish

41. Convergent evolution • Can often lead to cases of mimicry – the evolution of one organism so it comes to resemble or look like another. • Ex. Queen Anne’s butterfly closely resembles the toxic Monarch butterfly. • Over the course of time, the change of the gene pool of one species may lead to the change of the gene pool of another species – coevolution – when two species evolve in response to changes in each other. • Ex. Bats and moths • Flowers and insects

42. mimicry Queen Anne’s Butterfly Monarch Butterfly

43. coevolution

44. Patterns of evolution • Punctuated equilibrium – when long stable periods are interrupted by brief periods of more rapid change. • Gradualism – the idea that biological change is slow and steady. (supported by Darwin) • Scientists suggest that most new species are produced by periods of rapid change, because organisms evolve rapidly to fill available niches. • Example of punctuated equilibrium – Dinosaur species dominated Earth for over 100 million years. During this time, most mammals were small mouse-sized nocturnal organisms. Following the mass extinction of the dinosaurs, the small mammals rapidly diversified to fill available habitats and niches.

45. Evolution – a summary • Biological evolution • By natural selection – explains how life changes over time • Adaptation or adaptive traits enables an organism to survive through natural selection to reproduce under prevailing environmental conditions. • Biological evolution is based on changes in a population’s genetic makeup over time. • Populations evolve due to variations within, but individuals can’t develop new structures.

46. An ancient, changing earth • Earth is constantly changing and throughout history has had changes in • The atmosphere • Climate • Positions of continents • Geography • Types and number of organisms

47. Geology and a changing earth • James Hutton – proposed that layers of rock form slowly and that rocks are shaped by natural forces that operate over millions of years. • Charles Lyell – wrote Principles of Geology, which explained that processes that changed Earth in the past are still operating in the present.

48. Atmosphere and climate changes • Atmosphere • Changes in the atmosphere were the result of collisions between earth and large asteroids (catastrophic events) • Climate change • Alternate periods of heating and cooling • Advance and retreats of ice sheets over northern hemisphere

49. Interpreting Fossil evidence • Paleontologists – scientists who study fossils in order to determine animal behavior and climate conditions of the past. • Paleontologists determine the age of fossils using two techniques; • Relative dating – the age of a fossil is determined by comparing its placement with that of fossils in other horizontal layers of rock. • Problems – erosion, earthquake and volcanic activity can twist, fold and bend rock layers. • Radioactive dating – scientists calculate the age of a sample based on the amount of remaining radioactive isotopes it contains. • More exact method because the decay rate of each element is known. • Fossil record – provides evidence about the history of life on Earth. It also shows how different groups of organisms, including species, have changed over time.

50. How fossils form • For fossil to form, either the remains of the organism or some trace of its presence must be preserved.