Evolution
Jean-Baptiste Lemark 1744-1829 Lemark believed that change in organisms was due to use or disuse. He felt that if an organism needed to change in order to survive, it would change if it kept trying. The organism could then pass that new trait on to its offspring.
The giraffe needed to reach the leaves on the top of the trees, so he kept trying and trying until finally his neck stretched that far. He survived and passed the trait on. Lemark s Theory
1859 Darwin published On The Origin of Species Darwin believed in the theory of Natural Selection (Survival of the Fittest). His theory was that if an organism wasn t suited for its environment, then it would die and those traits would eventually die out of the population. Also, if you were better suited to survive, you would live and pass those traits on. Eventually, those favorable traits would become the norm.
1809-1882 Charles Darwin The Father of Evolution Born in England Naturalist (the study of nature) Studied medicine Degree in Theology theo = God, ology = the study of Buried in Westminster Abbey
After study at Cambridge, Charles was recommended for a surveying trip on the HMS Beagle The mission of the voyage was to chart stretches of the South American coast Darwin sailed aboard the Beagle for 5 years, working as a naturalist
This voyage lasted from 1831 to 1836
Boyage of the H.M.S. Beagle 5 year unpaid voyage Darwin studied plants, animals, collected fossils Found fossils of extinct animals that were similar to modern species On the Galapagos Islands in the Pacific Ocean Darwin noticed many variations among plants and animals of the same general type as those in South America
Many of Darwin s conclusions were based on observations of wildlife in the Galapagos Islands The Galapagos Islands are 500 miles west of South America in the Pacific Ocean, directly on the equator. Galapagos means turtle.
Darwin was influenced by: Sir Charles Lyell 1797-1875 Charles Lyell Geologist Contribution: Earth is very old (much older than thought) Earth has changed over time (constantly changing)
Darwin was influenced by: Thomas Malthus Thomas Malthus 1766-1834 Economist Contribution: Populations have the potential to increase faster than the available food supply
Darwin was influenced by: Wallace Botanist Contribution: Essay described evolution by natural selection Alfred Russel Wallace 1823-1913
Galapagos Finches Darwin noticed there were 13 types of finches in the Galapagos Islands; some species were confined to only one island Darwin observed these finches also all looked similar to a bird he had seen on the South American continent
The most distinct difference among finch species is their beaks, which are adapted for the specific diets available on the islands
Darwin wondered why these birds didn t look like the birds of the African continent since the environments of both the Galapagos and Africa were similar
Darwin guessed that some of the birds from South America migrated to the Galapagos Once on the islands, the birds must have changed over the years
large ground finch woodpecker finch cactus finch This would explain the numerous species of birds present
After returning from the Galapagos and studying all the different types of plants and animals. Darwin unified and explained his observations through the development of a new theory.
The Theory of Evolution Evolution means a change in species over time Darwin extended this principle to biology which helped form his theory of natural selection (survival of the fittest)
Natural Selection 1. All species have genetic variation 2. The environment presents challenges to survival 3. Individuals that are adapted to their environment survive and produce more offspring 4. Characteristics of fit individuals increase in a population over time
1. All species have genetic variation Individual characteristics vary within the same species Example: some beetles (of the same species) are green and some are brown http://evolution.berkeley.edu/evolibrary/
2. The environment presents challenges to survival There is constant struggle for survival Examples include: droughts/floods, fires/freezes, hurricanes, climate change, food, shelter, predation, disease, mating Example: green beetles tend to get eaten by birds and survive to reproduce less often than brown beetles do. http://evolution.berkeley.edu/ev olibrary/
3. Individuals that are adapted to their environment survive and leave more offspring than those who are not Fit individuals are organisms that are better adapted to their environment have a better chance of survival Organisms that possess favorable traits have a better chance of producing more offspring Example: The surviving brown beetles have brown baby beetles because this trait has a genetic basis. http://evolution.berkeley.edu/evolib rary/
4. Characteristics of fit individuals increase in populations over time These favorable traits of fit individuals are passed through generations Over time, the less favorable traits of less fit individuals are eliminated from the gene pool Example: The more advantageous trait (brown coloration) allows the beetle to have more offspring and becomes more common in the population. If this process continues, eventually almost all individuals in the population will be brown. (What would happen if a parasite prefers brown beetles, or if the environment was covered in green leaves?) http://evolution.berkeley.edu/evolibrary/
Darwin s contributions: Provided evidence that species evolve In 1859, he proposed the Theory of Natural Selection (Survival of the fittest) to explain the evolution of species Over time, change within species leads to the replacement of old species by new species as less successful species become extinct. Some evidence from fossils may prove that species on Earth have evolved from ancestral forms that are extinct. (species that have disappeared permanently.)
G. fuliginosa G. fortis Camarhynchus pauper G. magnirostris Cactospiza pallida C. psittacula G. scandens Cacts Finch (nectar,eeds, blood) C. heliobates Woodpecker-like Finch C. pauper G. conirostris Geospiza difficilis (seeds & insects) Insect-eating Finch Certhidea olivacea & C. Fusca This tree has how many major branches? Warbler Finch Seed-eating Finch Ground Finch Tree Finch Vegetarian Finch Platyspiza crassitrostris PHYLOGENIC TREE: A diagram showing the evolutionary history of a species of an animal
Scientific Evidence for Evolution: Fossil Record Comparative Anatomy Embryology DNA & Proteins (Biochemical Evidence) Embryology
Fossil Record A fossil is the mineralized remains of dead organisms How fossils form: Fossils usually form in swamps, ocean floors, tar pits, etc. The organism must be buried in sediment Calcium (bones, shells) ischemically altered
Fossil Record Lower layers indicate older fossils Upper layers indicate newer fossils Interpreting layers of fossils helps us infer the sequence of events in history
Equus, the modern horse, evolved from the dogsized Hyracotherium. Notice it evolved from a four-toed front foot to the one-toed front foot of the modern horse. Gradualism says that this happened gradually over millions of years. The evolution of the horse is an example of gradualism.
Punctuated Equilibrium says that these species existed in long periods of stasis interrupted by relatively brief periods of genetic instability that produced changes. This overall change still happened over millions of years. Evidence for both theories is observed in the fossil record.
Two Types of Evolution Convergent Evolution: process by which unrelated species become similar as they adapt to similar environments Divergent Evolution: formation of new species from an existing species adapting to new environments
Comparative Anatomy Homologous structures are characteristics that are shared by related species because they have been inherited in some way from a common ancestor A result of divergent evolution Structure is similar, but function is different
HOMOLOGOUS STRUCTURES: the fins of a porpoise, the wings of a bat, the leg of a horse, the bones in a human arm all have homologous bone structure, but perform different functions
Comparative Anatomy Analogous structures are similar in function but not in origin Organisms that occupy similar environments evolve similar features independently (parallel evolution) A result of convergent evolution (not common ancestry)
Convergent evolution example Sharks, dolphins, tuna, penguins have streamlined bodies, and fins. These similarities are NOT because they have a common ancestor. Sharks are cartilaginous fish, dolphins are mammals, tuna are bony fish, and penguins are birds. They share similarities because they both adapted to the same marine environment and predatory lifestyle.
Analogous structures
Comparative anatomy Vestigial structures found in modern species have no apparent purpose Examples: Tailbone (human) Tonsils (human) Appendix Canine teeth (human) Muscles to move ears (human) Whale pelvis
DNA sequencing The greater the similarity between the amino acid sequence of two organisms, the closer their evolutionary relationship A sequence of 3 DNA nucleotides (codon) correlates to 1 amino acid There is redundancy (more than one codon) for each amino acid
Which primates are most closely related?
Embryology Embryology is the study of organisms in their earliest stage of development. It traces similarities in development. For example, all chordate embryos have pharyngeal gill slits and post-anal tails. That s part of the definition of being a chordate.
What is a species? One or more populations of individuals that can interbreed, producing fertile offspring. Speciation is the process by which new species are formed over time.
Sometimes population ranges of different species overlap, but they still won t interbreed. Here are some reasons why: Mating incompatibility Physical Cyclical Behavior Geographical isolation
How does speciation occur? mating incompatibility Physical: for obvious reasons, crickets can t mate with giraffes, for example. They just don t have a common enough ancestor. Cyclical: For example, certain flowers and insects may prefer to mate at different times of day, may bloom at different times of the year, or may prefer different mating locations. So even if they are not geographically separated, they still won t mate with someone with a different schedule.
How does speciation occur? behavior Animals, especially, are picky. Some have elaborate mating rituals or specific traits they look for in a mate. For example, in some spiders and mantises, if the rituals aren t pleasing to the female, she will eat the male.
How does speciation occur? geographic isolation This is when populations of individuals are geographically separated and prevented from mating with one another. This can be due to the formation of new mountains, canyons, rivers, or other landforms, for example.
How does speciation occur? Over time, natural selection, acting on random mutations in the population, makes the DNA so different that the populations are no longer able to reproduce with each other Once there is no gene flow between the populations, mutations start to accumulate differently in each population and the populations diverge into different species. This is called macroevolution change on a grand scale including extinction and speciation.
Natural selection acts on individuals; Evolution (the change) is measured in populations. Microevolution is defined as the change in allele frequencies* in a population over generations. *Frequency how often something occurs expressed as a decimal; for example, if something occurs 50 out of 100 times, it has a frequency of 0.5
Hardy-Weinberg principle In 1908, two scientists independently came up with a mathematical way to measure if a population is evolving by measuring changes in allele frequencies. The equation assumes the following conditions: 1. Very large population 2. No migration 3. No net mutations 4. Random mating 5. No natural selection (if the above are occurring the population is most likely NOT going to evolve)
What causes genetic change in a population? Those conditions are never fully met. Therefore, the 4 main factors that cause change of allele frequencies in a population are: Natural selection Genetic drift Gene flow Mutation Of these, only natural selection adapts a population to its environment, and we ve already talked about it. The other three may be good or bad for a population or it may be neither good nor bad for it.
Genetic drift is change in allele frequency due to sampling error (chance) This factor is more pronounced when the population is small. Bottleneck effect occurs when a population is drastically reduced in size due to a natural disaster such as hurricane or disease, and many alleles are lost completely while others are over or under represented from what they were in the large population; ex) cheetahs; population is at risk due to a lack of genetic variability Founder effect occurs when a few individuals from a large population found (start) a new, isolated population ; ex) insects blown from the mainland to an island; humans moving from one continent to another and marrying within their own isolated community, such as the Amish in the U.S.
Gene flow is when the allele frequency of a population is altered by individuals moving into (or out of) a population. Another word for gene flow is migration.
Mutation As we have studied in past units, a mutation is a change in your DNA. This is the other factor that can change allele frequencies. A flower population with only blue alleles can sometimes produce a red flower due to mutation. That changes the allele frequency. In general, only things you were born with can be inherited. Things that change your appearance but are not genetic, such as tattoos or ear gauges, cannot be inherited. Even most mutations in your DNA cannot be inherited by your offspring. Think about why. What s the big exception?
Selective Breeding (Artificial Selection) Selective breeding is when humans select or breed in or out the traits that they want to be present in a species. This causes an artificial selection. The original traits may or may not become nonexistent. Could there be negative consequences of selective breeding?
Charles Darwin defined evolution as change in species over time The theory of evolution is based on Darwin s idea of natural selection Science has not yet explained the origin of life