Biology Chapter 15 Evolution Notes Section 1: Darwin's Theory of Evolution by Natural Selection Charles Darwin- English naturalist that studied animals over a number of years before developing the theory of evolution by Darwin's Journey: HMS Beagle- ship -primary mission, in 1831, was to leave England and survey the coast of South America. -over a year trip collected many fossils and animal/plant specimens Galapagos Islands: -Beagle arrived in 1835, Darwin was initially disappointed with the bareness -eventually saw two main things in wildlife: Finches: -He noticed that finch were different from island to island -He also noticed that finch beaks had slight changes even on the same island. What does this show us? Tortoises: -He noticed that shell shape and neck length changes from island to island based on what type of was available. When he returned home: -continued work with animals, especially breeding pidgins -saw he could breed them so make small changes for traits -called artificial selection What are some examples?
The Development of Natural Selection: -used some ideas of artificial selection to form the idea of natural selection Natural selection- survival of the "fittest", the rest will die and not pass on genes -in science "fitness" is the ability to and -given enough time, the population would change into a species Big idea: variation- change of traits throughout a population, leads to adaptations in certain adaptations- traits that give a species an in an environment -can change based on many factors. What are some? Darwin s book: -The Origin of Species by Natural Selection -the book that "shook the world" -led to term evolution -evolution- the cumulative changes in groups of organisms over time Section 2: Evidence of Evolution -Darwin's Theory of evolution by natural selection is part of the larger theory of evolution that is continuously being studied -The main idea of evolution is that all organisms descended from one Supporting evidence: Fossil record: -the record of all known to live on Earth -the structure of organisms from the past can give us an idea of how closely related to other organisms they are What can't we tell from fossils?
When studying fossils, scientists look at 2 types of traits Derived traits- newly evolved features that appear in the fossils of common ancestors Ancestral traits- more primitive traits that appear in ancestral forms -Transitional fossils are important to show the pattern of change ancestors to modern animals. Tracts the formation of derived traits. Comparative Anatomy: Why do structures in some animals look to be constructed the same but perform different functions? -evolution suggests that it is because there is a common ancestor Homologous Structures- anatomically similar structures inherited from a common ancestor - structure, function -forelimbs of vertebrate animals Analogous Structures: -similar structures in look that are not from a common ancestor - function, structure -birds wings and bugs wings Comparative Embryology: Embryo- an early, pre-birth stage of an organism s development -All vertebrates have a tail and pharyngeal pouches as embryos -in fish, the pouches become the gills, in reptiles, birds, and mammals, they become part of the ears, jaws, and Comparative Biochemistry -the presents of certain complex metabolic molecules that many different organisms share could show how closely related they are. -chromosome C enzyme -a molecule that is essential for respiration -has not changed much over time from species to species -DNA and RNA are also looked at to see patterns -give more that the fossil record
Geographic Distribution: -a change in species based on the they live in -Darwin's finches -similar species also derive from where they were originally from before the continents drifted. -Biogeography- the study of the distribution of plants and animals around the world Section 3: Shaping Evolutionary Theory -the central theme of evolution is that natural selection and variation can lead to new species over time, but this is not the only theme in evolution. It can also be used and built on through population genetics Genetic Drift: -any change in the frequencies in a population that results from chance -"can't pick who your parents are" -2 types that we will learn about -Founder Effect- occurs when a small group of a population settles and is separated from the rest of the population -the genes and traits they bring are -can cause uncommon traits to become common in that population -Old Amish Order- high amounts of 6 finger dwarfism -Bottleneck effect- happens when a population declines to a very low number then -can lead to inbreeding -causes populations to be very -African cheetahs Other Factors of Genetic Drift: -Gene flow: -the coming and going of individuals in a population -immigration and emigration -Nonrandom mating: -certain factors effect what species mate -examples?
-Mutation: -sometimes provide for survival -Natural selection: -4 main types -stabilizing selection: -most common form -eliminates extreme because the average one has the most fitness -baby weights -Directional selection: -when an version of a trait makes the organism more fit -English Moths -Darwin's Finches -Disruptive selection: -splits population into 2 groups with phenotypes -depends on environment they live in -snakes on rocky island shores and grassland snakes color -Sexual Selection: -changes frequency of trait based on what the opposite finds attractive -sometimes are opposite of what causes survival -birds are extreme with this Reproductive Isolation: -the process whereby some members of a sexually reproducing population change so much that they cannot produce offspring with members of the original population -2 types Prezygotic isolation- prevent reproduction by making fertilization unlikely -prevent genotypes from entering gene pool through geographic ecological, behavioral, or other differences -Western meadowlark and Eastern meadowlark -live in same places and look -use different mating songs -different species of trout live in same steam but breed at different times of the year
Postzygotic isolation: -fertilization occurs but the offspring cannot reproduce -male donkey and female horse make a -male lion and female tiger make a liger Speciation: -they are separate species that cannot reproduce -the process in which populations create 2 different species that are not able to mate -2 types -allopatric speciation- a physical barrier divides one population into two or more populations -when enough time passes, they will no longer be able to mate -some say it is for speciation -Abert and Kaibab squirrels, separated by Grand Canyon -sympatric speciation- a species evolves without a physical barrier -evidence seen in some species -thought to happen fairly frequently in plants Patterns of Evolution: -Adaptive radiation- when several species diverge from a single ancestor within a short period of time in response to the creation of a or another ecological opportunity -300 species of cichlid fish that once lives in Africa's Lake Victoria -mammals at the beginning of the Cenozoic era following the extinction of the dinosaurs -Coevolution- when species evolve in close relationship with other species -could be mutualism or defense mechanisms -orchids and moths developed traits that help pollination -plants evolve new defense mechanisms to prevent insects from eating them, insects evolve new ways to eat them -Convergent Evolution- unrelated species evolve traits even though they live in different parts of the world -happens when places they live have similar ecology -Australian Marsupials and Placental Mammals
-Rate of speciation: -2 theories -gradualism- traits develop through gradual steps over a very long time -punctuated equilibrium- rapid spurts of genetic change cause species to quickly -evidence supports both, scientist still don't know which one is more common