EVOLUTION. Chapters 15, 16, and 17. 15.1 The Puzzle of Life ’ s Diversity. I. Evolutionary Theory A. Evolution – a change (in a kind of organism) over time; a process by which modern organisms have descended from ancient organisms. 15.1 The Puzzle of Life ’ s Diversity.
Chapters 15, 16, and 17
I. Evolutionary Theory
A. Evolution – a change (in a kind of organism) over time; a process by which modern organisms have descended from ancient organisms.
B. Theory – a well-supported testable explanation of phenomena that have occurred in the natural world.
C. Darwin’s voyage of the Beagle
1. Darwin made numerous observations and collected evidence that led him to propose a revolutionary hypothesis about the way life changes over time.
2. That hypothesis has become the theory of evolution.
II. Darwin’s Observations
A. Patterns of Diversity
1. Darwin observed that plants and animals seemed to be well suited to their environment.
2. He observed the different way organisms survive and reproduce.
3. He also observed how similar ecosystems on different continents had different species rather than similar species.
B. Living Organisms and Fossils
1. fossils – preserved remains of ancient organisms.
2. Darwin collected living organism and fossils.
3. Darwin observed how some fossils look similar to organisms still alive and others looked like nothing he had ever seen.
C. The Galapagos Islands
1. The Galapagos Islands influenced Darwin’s studies the most.
2. The climate of each Island differed even though they are close together.
3. Darwin noted that the land tortoises and marine iguanas varied in predictable ways from island to island.
Ex. The shape of the tortoise’s shell.
Pinta IslandIntermediate shell
III. The Journey Home
A. On the journey home, Darwin studied the animals he collected and his findings.
B. He noticed that mockingbirds collected from different islands looked different from each other.
C. Darwin’s observed that the characteristics of many animals and plants varied noticeably among the different islands of the Galapagos.
1. He wondered if animals on different islands had once been members of the same species.
2. He concluded that these separate species would have evolved from the original South American species after becoming isolated from one another.
I. Lamark’s Evolution Hypotheses
A. Lamark was one of the first scientists to recognize that living things change over time, all species were descended from other species, and organisms are adapted to their environment.
B. Lamark’s hypothesis – that by selective use or disuse of organs, organisms acquired or lost certain traits during their lifetime. These traits could then be passed on to their offspring. Over time, this process led to changes in a species.
1. Tendency toward Perfection
Organisms are continually changing and acquiring features that help them live more successfully in their environment.
2. Use and Disuse
Organisms can alter the size and shape of organs by using their bodies in new ways or by not using particular organs.
3. Inheritance of Acquired Traits
If an organism alters a body structure, those altered traits can be inherited.
C. Evaluating Lamark’s hypothesis
1. Lamark did not know how traits were inherited.
2. He did not know an organism’s behavior had no effect on its heritable traits.
3. Lamark was one of the first to develop a hypothesis of evolution and realized organisms adapt to their environments.
II. Population Growth (1798)
A. Malthus reasoned that if human population continued to grow unchecked, sooner or later there would be insufficient livingspace and food.
B. Forces that work against growth were war, famine, and diseases.
I. Inherited Variation and Artificial Selection
A. Inherited Variation
1. Darwin observed variation in species existed in nature and on farms.
2. Some of these variations were heritable, meaning the can be passed from parents to offspring.
3. Breeders used heritable variation to improve crops and livestock.
B. Artificial Selection – selection by humans for breeding of useful traits from natural variation among different organisms.
II. Evolution by Natural Selection
A. The Struggle for Existence
1. Darwin was convinced that artificial selection worked in nature.
2. Struggle for existence – members of each species compete regularly to obtain food, living space, and other necessities of life.
3. The biggest, strongest, faster, better camouflaged, or better protected were able to survive.
B. Survival of the Fittest
1. A key factor in the struggle for existence was how well suited an organism is to its environment.
2. Fitness – the ability of an individual to survive and reproduce in its specific environment.
3. Adaptation – any inherited characteristic that increases an organism’s chance of survival.
4. Adaptations can be anatomical or structural, physiological processes or functions, and behavior.
5. Survival of the fittest – Individuals of a species that are better suited to their environment survive and reproduce most successfully.
6. Natural Selection – Darwin referred to survival of the fittest as natural selection.
7. Over time, natural selection results in changes in the inherited characteristics of a population. These changes increase a species’ fitness in its environment.
III. Evidence of Evolution
A. Darwin argued that living things have been evolving on Earth for millions of years. Evidence for this process could be found in the fossil record, the geological distribution of living species, homologous structures of living organisms, and similarities in early development, or embryology.
B. Fossil Record
1. Fossils – remains of ancient life.
2. Scientist compare fossils in older rock layers with fossils in younger rock layers and could document how species changed over time.
C. Geographic Distribution of Living Species
1. Darwin observed entirely different species on different continents.
2. Yet, these continents had similar environments and the different species had similar anatomical structures and behaviors.
3. Because of the similar ecological conditions, these species are exposed to similar pressures of natural selection. Because of these similar pressures, different animals ended up evolving similar features.
D. Homologous Body Structures
1. Homologous structures – structures that have different mature forms but develop from the same embryonic structures. Ex. The forelimbs of vertebrates.
2. Homologous structures provide strong evidence that all four-limbed vertebrates have descended, with modifications, from common ancestors.
3. Similarities and differences help biologists group animals according to how recently they last shared a common ancestor.
Ancient lobe-finned fish
4. vestigial organs – organs that are reduced in size that they are just vestiges or traces, of homologous organs.
E. Similarities in Embryology
1. Many species look similar during the early stages of development.
2. Some groups of embryonic cells develop in the same order and in similar patterns to produce tissues and organs of all vertebrates.
3. These common cells and tissues produce the homologous structures discussed earlier.
The fossil record
Geographic distribution of living species
Homologous body structures
Similaritiesin early development
Physical remains of organisms
Common ancestral species
Evidence of Evolution
which is composed of
IV. Summary of Darwin’s Theory
A. Individual organisms differ, and some of this variation is heritable.
B. Organisms produce more offspring than can survive, and many that do survive do not reproduce.
C. Because more organisms are produced than can survive, they compete for limited resources.
D. Individuals best suited to their environment survive and pass their heritable traits to their offspring.
E. The process where diverse species evolved from common ancestors, unites all organisms on Earth into a single tree of life.
V. Strengths and Weaknesses of Evolutionary Theory
A. Evolutionary theory offers vital insights to all biological and biomedical sciences, from infectious-disease research to ecology. Evolution is called the “grand unifying theory of the life sciences.”
B. Evolution theory is continually changing as new data are gathered and new ways of thinking arise.
A. Speciation - the formation of new species.
B. Species - is a group of organisms that breed with one another and producefertileoffspring.
1. This means that individuals in the same species share a common gene pool.
2. A genetic change that occurs in one individual can spread through the population.
3. If the genetic change increases fitness, that allele will eventually be found in many individuals of that population.
II. ISOLATING MECHANISMS
A. The gene pools of two populations must become separated for them to become new species.
1. As new species evolve, populations become reproductively isolated from each other.
a. reproductive isolation - when the members of two populations cannot interbreed and produce fertile offspring.
b. Populations respond to natural selection or geneticdrift as separate units.
B. Reproductive isolation can develop in a variety of ways, including behavioral isolation, geographic isolation, and temporal isolation.
1. BEHAVIORAL ISOLATION – occurs when two populations are capable of interbreeding but have differences in courtship rituals or other reproductive strategies that involve behavior. Example: eastern and western meadowlarks use different songs to attract mates.
2. GEOGRAPHIC ISOLATION – two populations are separated by geographic barriers such as rivers, mountains, or bodies of water. Example: the Abert squirrel and the Kaibab squirrel.
3. TEMPORAL ISOLATION – two or more species reproduce at different times. Example: three species of orchids release pollen on different days.
Different mating times
which result in
which result in
Formation ofnew species
III. TESTING NATURAL SELECTION IN NATURE
A. Darwin’s Finch
1. Darwin hypothesis was that natural selection shaped the beaks of different finches as they adapted to eat different foods.
2. Peter and RosemaryGrant studied the finches of the Galapagos Islands to prove Darwin’s theory.
3. They realized that Darwin’s hypothesis relied on two testable assumptions:
a. in order for beak size and shape to evolve, there must be enough heritable variations in those traits to provide raw material for natural selection.
b. differences in beak size and shape must produce differences in fitness that causes natural selection to occur.
1. First, the Grants identified and measured as many individual on the island.
2. Characteristics they measured were differences in wing length, leg length, beak length, beak depth, beak color, feather colors, and total mass.
3. These data indicated that there is great variation of heritable traits among the Galapagos finches.
C. NATURAL SELECTION
1. During the rainy season when food is abundant, finches used the food source most available.
2. During drought, finches eat the food that their beak can handle best.
3. Individual birds with different-sized beaks had different chances of survival during drought. Ex. The birds with the largest beaks were more likely to survive.
4. The Grant’s observed that the average beak size in the finch population increased over time.
D. RAPID EVOLUTION
1. The Grant’s provided evidence of the process of evolution: the next generation of finches had larger beaks than the generation before selection had occurred.
2. Natural selection can take place frequently and rapidly.
IV. SPECIATION IN DARWIN’S FINCHES
A. Natural selection can lead to speciation
1. Speciation in the Galapagos finches occurred by founders forming a new population, geographic isolation, changes in the new population’s gene pool, reproductiveisolation, and ecological competition.
B. FOUNDERS ARRIVE
1. Many years ago, a few finches (species A) flew or were blown from South America to the Galapagos islands.
2. Once they arrived, they managed to survive and reproduce.
C. SEPARATION OF POPULATIONS
1. Later a few finches flew to another island.
2. They became isolated from each other because finch do not fly over open water.
3. They no longer share the same gene pool.
D. CHANGES IN THE GENE POOL –
1. Over time, populations on each island became adapted to their local environments.
2. Food supplies may have been different and one group developed larger beaks forming a separate population.
E. REPRODUCTIVE ISOLATION
1. Finches mate with other finches that have bills the same size as their own.
2. Even if the finches wind up on the same island, the gene pools of the two bird populations remain reproductively isolated.
3. The two population then become separate species.
F. ECOLOGICAL COMPETITION
1. If the two types of finches wind up on the same island there will be competition for food.
2. The more specialized birds have less competition for food.
3. Over time, species evolve in a way that increases the differences between them.
G. CONTINUED EVOLUTION
1. The process of isolation on different islands, genetic change, and reproductiveisolation probably repeated itself time and time again across the entire Galapagos island chain.
2. Over many generations it produced 13 different finch species.
I. Fossils and Ancient Life
A. paleontologist - scientists who study fossils
1. fossil record - provides information about the history of life on Earth and shows how different groups of organisms, including species, have changed over time.
2. Fossils occur in a particular order.
Ex: certain fossils only appear in older rocks, and other fossils only appear in more recent rocks
3. More than 99percent of all species that have ever lived on Earth have become extinct, which means the species died out.
4. Over billions of years, ancient unicellular organisms have given rise to the modern bacteria, protists, fungi, plants, and animals.
II. Interpreting Fossil Evidence
A. Exposing Fossils
1. The natural forces (earthquakes, wind, rain, running water) that form sedimentary rock can also reveal fossils that have been hidden in layers of rock for millions of years.
Formation of a Fossil
Water carries small rock particles to lakes and seas.
Dead organisms are buried by layers of sediment, which forms new rock.
The preserved remains may later be discovered and studied.
B. Relative Dating
1. In relative dating, the age of a fossil is determined by comparing its placement with that of fossils in other layers of rock.
2. Scientists use index fossils to compare the relative ages of fossils.
3. To be used as an index fossil, a species must be easily recognized and must have existed for a short period but have had a wide geographical range.
4. Relative dating allows paleontologists to estimate a fossil’s age compared with that of other fossils.
C. Radioactive Dating
1. Radioactive elements found in rock decay, or break down, into nonradioactive elements at a steady rate.
2. half-life - the length of time required for half of the radioactive atoms in a sample to decay.
3. Radioactive dating is the use of half-lives to determine the age of a sample.
4. Scientists calculate the age of a sample based on the amount of remaining radioactive isotopes it contains.
Ex.: Carbon-14 has a half-life of about 5730 years.
Age of fossil with respect to another rock or fossil (that is, older or younger)
Age of a fossil in years
Comparing depth of a fossil’s source stratum to the position of a reference fossil or rock
Determining the relative amounts of a radioactive isotope and nonradioactive isotope in a specimen
Imprecision and limitations of age data
Difficulty of radioassay laboratory methods
Comparing Relative and Absolute Dating of Fossils
Is performed by
I. Macroevolution- large-scale evolutionary patterns and processed that occur over long periods of time
A. Extinctions happen for reasons Darwin proposed
1. Species compete for resources and environments change
2. Some species adapt and survive, and others gradually become extinct in ways that are often caused by natural selection
3. Many paleontologists think mass extinctions were caused by several geological factors
4. Each disappearance of so many species left habitats open and provided ecological opportunities for those organisms that survived.
Ex: the extinction of dinosaurs cleared the way for the evolution of modern mammals and birds
III. Adaptive Radiation
A. Adaptive radiation - a single species or a small group of species has evolved into diverse forms that live in different ways
1. Ex: Darwin’s finches -more that a dozen species evolved from one single species
IV. Convergent Evolution
A. Convergent evolution - the process by which unrelated organisms come to resemble one another
1. caused by similar environmental demands, such as moving through air, moving through water, or eating similar foods
2. Ex.: the streamlined body and various appendages of a shark (fish), a penguin (bird), and a dolphin (mammal)
A. coevolution - the process by which two species evolve in response to changes in each other over time
1. caused by the ecological interactions between organisms
2. Ex.: shape of flower and moth’s feeding tube (p. 438)
VI. Punctuated Equilibrium
A. Evidence suggests that evolution has often occurred at different rates for different organisms at different times during the history of Earth
B. punctuated equilibrium - pattern of long, stable periods interrupted by brief periods of more rapid change
Intense environmental pressure