Evolution 3/2/14
So what is Evolution anyway? Definition: A change over time More specifically: change in relative frequency of alleles in a population Note the word POPULATION INDIVIDUALS DO NOT EVOLVE
Sources of Change 1. Sexual Reproduction ( Random Shuffling of alleles) 2. Mutations 3. Geographic isolation
So, What does Darwin have to do with it?
Charles Darwin Born in England February 12, 1809 to a wealthy family attended Oxford University became a naturalist joined the crew of the H.M.S. Beagle for a 5 year voyage (1831)
What Darwin learned from the voyage made numerous observations and collected data that led him to propose a revolutionary hypothesis about the way life changes (evolution).
Darwin s Observations:1. Patterns of Diversity plants and animals are well suited to whatever environment they inhabit
2. Living Organisms and Fossils collected remains of preserved organisms called fossils. Some of the fossils resembled organisms that were still alive and others looked completely unlike any creature he had ever seen.
3. The Galapagos Islands characteristics of many animals and plants varied noticeably among the different Galapagos Islands. Ex. The tortoises shape of the shell corresponded to different habitats. Hood Island tortoise long neck and curved shell that is open and allows it reach sparse vegetation
Hood Island Isabela Island(below) Pinta Island
Other Organisms noticed that the finches on the Islands all had different beaks likely that a few finches founded the population but mutations over time allowed them to eat different foods. New beaks continued to be passed to the next generation which eventually led to different species
Variety of Finches
Plants also undergo the same pressures of the environment Variety of vegetation found based on the type of climate that exists
Evolution by Natural Selection Definition: process by which individuals that are better suited to their environment survive and reproduce most successfully.
Artificial Selection using genetic variation to improve crops or livestock ; artificial selection Artificial selection: nature provided the variation and humans select those variations that they found useful. EX: dogs, horses, corn, tomatoes, pig, cow, etc.
Not a random process! The mutation is random, but selection acts on that variation in a very non-random way: genetic variants that aid survival and reproduction are much more likely to become common than variants that don't. (University of Berkeley)
5 major points to natural selection 1. Genetic variations exist in populations. Some variations are more favorable than others. These variations are inherited. 2. Organisms produce more offspring than can survive. Those that do not survive, do not reproduce.
3. Overproduction of offspring forces competition for resources. Darwin called this the struggle for existence. Not all offspring can possibly survive. 4. Individuals with favorable variations have more fitness ;more likely to survive and pass those variations on to their offspring.
5. Species alive today are descended with modification from ancestral species that lived in the distant past. Darwin called this descent with modification.
Survival of the Fittest Link to Natural Selection example cartoon Adaptations: any inherited trait that increases the chances of survival and reproduction of an organism. Examples are: Camouflage and Mimicry allow animals with successful variations survive and reproduce EXAMPLES IN NATURE: Mimicry:Monarch and Viceroy, Moth and Bumblebee Camouflage: Squirrels, Leopards, walking sticks, Praying Mantis
There are many more adaptations besides camouflage and mimicry. (Behaviors, sounds, etc.)
Evidence of evolution 1 Fossils and the fossil record 2 Geographic distribution 3 Homology 4. Vestigial Structures 5 Embryology 6 Biochemistry (the chemistry of living organisms)
Sue, the largest, most complete T. rex fossil ever found. It resides at the Field Museum in Chicago. A 12,000 year old mammoth
1. Fossils Remnants of organisms left behind Ex: Scientists can compare the bones of horses from 4 million years ago to ones from the present day. Fossils found in every layer of rock do not look the same as those from modern life. The oldest fossils are more different from the modern day organisms than the shallowest fossils
2) Geographic distribution similar animals in very far away places.( Rheas, Emus, and Ostriches) Animals use different adaptations to survive in similar environments even though the environments are separated. Analogous Structures: Different in Structure but the same in function These do not show evidence of evolutionary relationships but, they do show natural selection.
3. Homology Many organisms have similar bones and are closely related. These are called Homologous structures. Suggest a common ancestor and shows strong evolutionary relationships Example: Birds, turtles, alligators, rats, humans, and whales all have same arm bones
Put picture of human, horse, cat, bat, bird, whale here
4. Vestigial structures any structure that is so reduced in function or size that they are just vestiges or traces of the original structure. The structure may have been used in an ancestor. The structure may be used in another animal alive today. Examples: Appendix, small leg bones in pythons, pelvic bones in whales Tonsils actually DO HAVE A FUNCTION even though they can be removed.
Whale ancestors with legs Whales are mammals that have no hind legs. They are thought to have evolved from 4-legged land animals that lived over 50 million years ago. Paleontologists expected to find whale ancestors that showed reduced and vestigial legs by looking in sediments that were between 50 and 30 million years old. Some examples of this transition are shown below. Ambulocetus 49 million years ago Pakicetus 42 million years ago Basilosaurus 40 million years ago
Picture of vestigial structures The fish Astyanax comes in two varieties the surfacedwelling varitey is on the left, the eyeless cave fish is on the right.
5. Embryology Of animals with backbones, the embryonic stages look strikingly similar ; similar genes at work
What does this suggest? Suggests a common ancestor and evolutionary relationships Groups of embryonic cells develop in the same order and in similar patterns; same genes (* Hox genes) turn on and off during periods of development. (From fruit flies to humans)
6. Biochemistry The more closely related organisms are, the more they will share in common biochemistry (the chemistry of what makes up their bodies) similar DNA sequences and proteins Relatively new means of identifying evolutionary relationships has led to the re-organization of the history of several species * can tell when species diverged from one another
Chapter 17 notes: Evolution and Populations
Ch. 17 Is all evolution the same? No, it does not happen in the same way across all populations. Genetic variation in organisms is studied at the level of a population not the individual. A population is a group of individuals of the same species that live in the same area.
populations Members of a population of species interbreed, therefore they share a common group of genes called a gene pool. Gene Pool: all of the genes that are present in a population. This includes all the different alleles.
The relative (allelic) frequency of an allele is the number of times that the allele occurs in a gene pool compared to the number of times other alleles for the same gene occur. Q: How do new alleles arise? Through random mutations. Gene shuffling during meiosis Crossing over Sexual Reproduction
Recall from Ch.16 evolution : any change in the relative frequency of alleles in a population. if the frequency of the allele changes, then the population is evolving.
RECALL from genetics Inheritable variation can be expressed by either single-gene traits or by polygenic traits. The number of phenotypes produced for a given trait depends on how many genes control the trait.
Evolution can occur in three ways Directional selection Stabilizing Selection Disruptive Selection
Populations Most phenotypes in generations form a bell shaped curve The most common variety is represented in the middle of the curve and more extreme variations are on either end of the curve. * (hair color) Evolution shifts the curve by changing the percentage of each variation.
Directional selection Individuals on one end of the curve are better adapted to their environment. EXAMPLE: Beak size (finches) The birds with the medium beak are the majority. Small and large beaks are on the ends of the curve. If a drought occurs and only the very large seeds survive, only largebeaked birds will be able to eat.
Directional selection The average beak size increases since more of the larger beaked finches could survive and reproduce.
Stabilizing selection When the average individual is best, the population stabilizes-reduces the percentage of organisms on the extremes Example: Birth weight in humans stays stable because too small a weight is harmful for the baby and too big a weight results in complications at birth.
Stabilizing selection
Disruptive selection This occurs when either extreme is better adapted for survival than the average. EXAMPLE: most of a species of a butterfly are brown. But, on either end of the population curve, you see RED and BLUE Brightly colored butterflies resemble very poisonous butterflies and thus, do not get eaten.
Disruptive selection
Small populations The percentages of alleles change more quickly- GENETIC DRIFT random change in allelic frequency Two Types of Genetic Drift: 1) If populations get separated and each new population only has two of the four variations, you have what is called a FOUNDER EFFECT Def: Change in allele frequencies as a result of migration of a small subgroup
FOUNDER EFFECT
Bottleneck Effect *add into notes 2) Change in allelic frequency after a dramatic reduction in the size of a population. Example: a natural disaster such as a tornado or hurricane wipes out a population but a few individuals remain. Those individuals may have very different alleles from the original population. Therefore, the population that grows will be different from the original population.
ARE POPULATIONS ALWAYS EVOLVING? No, but there are 5 conditions which must be met for a population not to be evolving. Requirements to maintain genetic equilbrium: 1) Random mating In nature, random mating rarely occurs. Example: Lions select their mates based on size or strength.
2) Large population 3) No movement into (immigration) or out of population (emmigration) 4) No mutations 5) No natural Selection THIS IS KNOWN AS THE HARDY- WEINBURG PRINCIPLE
It is difficult for all of the conditions to be met.
So, how do we get a new species? 17.3 All of these changes over time can eventually lead to a new species This process is called SPECIATION
3 types of speciation Caused by 3 isolating mechanisms: Behavioral Geographic Temporal
Behavioral isolation Occurs when two populations are capable of interbreeding but do not. (due to difference in rituals/ behaviors) EX: Eastern and Western meadowlarks both live in central US They do not mate because they use different songs to attract their mates
Geographic isolation occurs when 2 populations cannot reach each other to mate due to a physical barrier. EX: earthquake in CA creates a huge crevasse in the ground, isolating a population of lizards Since the two populations cannot mate, they begin to have subtle changes over time that make them different species
Temporal isolation Occurs when the species reproduce at different times of the year. EX: 3 species of orchid all live in the same area but, they never interbreed because they release their pollen at different times of the year.
orchids
CH. 19 History of Life on earth 4/13/15 And, should I become a paleontologist rather than a dentist?
Ch. 19 Geologic evidence shows that Earth is about 4.6 billion years old.
By the fossil record, scientists have learned that not all types of animals appeared all at once. Fact: more than 99 percent of all species that have ever lived on Earth have become extinct. Earliest life forms appeared in rocks more than 3.5 billion years old. Paleontologists scientists who study fossils
Fossils what do you look at? 1.Anatomical similarities and differences between the fossil organism and organisms living today. 2. The fossil s age. 3. What the environment may have been like when the organism was alive. This may tell you what the organism ate and how it lived.
Dating Methods 1) Relative: The age of the fossil is determined by comparing its placement in the sedimentary rock with that of fossils in other layers Index fossils are used
What are index fossils? Fossils of a species that are easily recognized. Existed for only a short period of time so it will only be found in a few layers of rock. Had a wide geographic distribution. * meaning that it can be found in many locations around the world.
Rocks and sediments are deposited on the earth in layers. By looking at the layers, we can tell what order they were deposited in. What does this show? change in species through time
Radioactive dating link *2:58 To 50 seconds then fast forward to 2:58 to 3:28 2) Radioactive: calculate absolute ages of the fossil based on the amount of remaining radioactive isotope it contains. Different radioactive isotopes have different half-lives (rates of decay). Half Life: time it takes for half of the radioactive atoms in a sample to decay EX: Carbon-14: decays into nitrogen-14 every 5739 years which is called the half-life. EX: Potassium-40: decays into argon- 40 every 1.26 billion years.
How does Radioactive dating work exactly? (carbon dating) All plants and animals incorporate carbon into their tissues during their lives for growth and energy. (eating) When an organism dies, it stops incorporating carbon (all forms of carbon, including C14) into its structure. The amount of radioactive carbon (C14) that had been in the organism when it was alive begins to decrease at death as it loses nuclear particles through radioactive decay. C14 is only good for dating fossils younger than 60, 000 years old the "clock" starts ticking when death occurs.
Sequence of events (per the geologic record) Early bacteria-like cells/ prokaryotes First Eukaryotes Fish and simple plants Amphibians Reptiles and bush-like plants Birds and trees Simple mammals (rodents) Primates
What was the Earth like before PreCambrian time? Link *after 4:07 Earth s atmosphere did not contain oxygen, so microorganisms were the first to appear (prokaryotic).in the water Once oxygen appears, eukaryotic organisms appear. Theory of Endosymbiosis Eukaryotic cells arose from living communities formed by prokaryotic cells.
Theory of endosymbiosis Mitochondria and chloroplasts contain their own DNA Mitochondria and chloroplasts have ribosomes that make their own proteins. Like bacteria, mitochondria and chloroplasts have many of the features of free-living bacteria such as being able to grow and reproduce independently of the cell.
A Brief History of Time Since all organisms have appeared sequentially, it would seem logical to assume that each gave rise to the other.. This is not the case. Evolution states that organisms share ancestors not that one evolved into another.
Rates of Evolution Evidence shows that evolution has proceeded at different rates for different organisms at different times. 1.) Gradualism- Gradual change/ slow and steady change 2.) Punctuated Equilibrium- equilibrium interrupted by brief periods of rapid change. Rapid can mean a few thousand years in terms of geologic time.
The Peppered Moth link
Rapid evolution occurs most frequently in small populations. EX: - founder effect, bottleneck effect
Patterns of evolution in populations Adaptive radiation Convergent evolution Coevolution extinction
Adaptive radiation/ divergent evolution A single species evolves into more populations by creating adaptations to different environments or niches EX: Galapagos finches Hawaiian Fruit flies -
Convergent evolution Unrelated organisms resemble each other since they have adapted to the same environment. Ex: fish and dolphins both have fins Ostriches, Rheas, and Emus, Flying Squirrels and Sugar Gliders Birds and dragonflies both have wings RECALL: These are called analogous structures ( same function but different structure)
Coevolution When two species evolve in response to one another EX: Flowers and their pollinators must evolve together. If the flower has a mutation that no longer attracts the hummingbird, it will not reproduce.and then, the hummingbird will have to find a new food source.
Extinction When a species cannot adapt to its changing environment Competition Climate change
So much to learn, so little time! Evolution is a whole course in college all by itself!