Evolution

What is evolution? Evolution is defined as “descent with modification” a.k.a. “Change over time” Over a large number of years, evolution produces tremendous diversity in forms of life. Leaves on trees change color and fall over several weeks. Mountain ranges erode over millions of years.

Isn’t Evolution ‘just’ a theory? Scientific theories are explanation that are based on lines of evidence, enable valid predictions, and have been tested in many ways. In contrast, there is also a popular definition of theory – a “guess” or “hunch” These conflicting definitions cause some confusion when it comes to evolution…

Descent with modification??? We’ve defined evolution as descent with modification from a common ancestor, but exactly what has been modified? Compare these two examples of change in beetle populations. Which one is an example of evolution? Beetles on a diet Imagine a year or two of drought in which there are few plants that these beetles can eat. All the beetles have the same chances of survival and reproduction, but because of food restrictions, the beetles in the population are a little smaller than the preceding generation of beetles. Beetles of a different color Most of the beetles in the population (say 90%) have the genes for bright green coloration and a few of them (10%) have a gene that makes them more brown. Some number of generations later, things have changed: brown beetles are more common than they used to be and make up 70% of the population. Which example illustrates descent with modification—a change in gene frequency over time?

Who is Charles Darwin? An English scientist Considered the “father of modern evolutionary theory” Studies animal and plant life as a ship’s naturalist. From these findings he was able to develop his theory of evolution

The Galapagos Islands Aboard the H.M.S Beagle, Darwin traveled to the Galapagos Islands The Galapagos supports a great deal of diversity in both plant and animal life Darwin studied & compared the anatomy of many species of: Reptiles Insects Birds** Flowering plants All of which were unique to the island, but similar to species found around the world

Darwin notices struggles Competition for space & food Need to escape from predators Need to find enough prey Ability to find AND secure shelter SURVIVAL OF THE FITTEST…

What is Natural Selection? Natural selection is one of the basic mechanisms of evolution, along with mutation, migration, and genetic drift. Darwin’s grand idea of evolution by natural selection is relatively simple but often misunderstood.

To find out how Natural Selection works, imagine a population of beetles: There is variation in traits. For example, some beetles are green and some are brown There is differential reproduction. Since the environment can’t support unlimited population growth, not all individuals get to reproduce to their full potential. In this example, green beetles tend to get eaten by birds and survive to reproduce less often than brown beetles do.

To find out how Natural Selection works, imagine a population of beetles (continued…) There is heredity. The surviving brown beetles have brown baby beetles because this trait has a genetic basis. End result: The more advantageous trait, brown coloration, which allows the beetle to have more offspring, becomes more common in the population. If this process continues, eventually, all individuals in the population will be brown.

Natural Selection Overview In nature, there is a tendency towards the overproduction of offspring In any population of organisms, individuals will exhibit slight variations Individuals with variations that are favorable for a particular environment are more likely to survive and pass those variations on to the next generation than are individuals with less-favorable variations Gradually, offspring of survivors will make up a larger proportion of the population and eventually a population may look entirely different

What is fitness? Biologists use the word fitness to describe how good a particular genotype is at leaving offspring in the next generation relative to how good other genotypes are at it. Fitness is a relative thing. A genotype’s fitness depends on the environment in which the organism lives. The brown beetles have a greater fitness relative to the green beetles.

Fitness in Nature A B C Caring for your offspring (A), and producing thousands of young — many of whom won't survive (above right), and sporting fancy feathers that attract females (left) are a burden to the health and survival of the parent. These strategies do, however, increase fitness because they help the parents get more of their offspring into the next generation.

Mechanisms of Evolution Mutation A mutation could cause parents with genes for bright green coloration to have offspring with a gene for brown coloration. That would make the genes for brown beetles more frequent in the population. Migration Some individuals from a population of brown beetles might have joined a population of green beetles. That would make the genes for brown beetles more frequent in the green beetle population.

Mechanisms of Evolution Genetic Drift Imagine that in one generation, two brown beetles happened to have four offspring survive to reproduce. Several green beetles were killed when someone stepped on them and had no offspring. The next generation would have a few more brown beetles than the previous generation—but just by chance. These chance changes from generation to generation are known as genetic drift. Natural Selection Imagine that green beetles are easier for birds to spot (and hence, eat). Brown beetles are a little more likely to survive to produce offspring. They pass their genes for brown coloration on to their offspring. So in the next generation, brown beetles are more common than in the previous generation.

Evolution Mechanisms Understood Mutation… Migration… Genetic Drift… Natural Selection… All of these mechanisms can cause changes in the frequencies of genes in populations, and so all of them are mechanisms of evolutionary change. However, natural selection and genetic drift cannot operate unless there is genetic variation—that is, unless some individuals are genetically different from others. If the population of beetles were 100% green, selection and drift would not have any effect because their genetic make-up could not change.

Natural Selection & Adaptation Any trait that aids the chances of survival and reproduction of an organism Can be explained by applying Darwin’s theory of natural selection We will focus on two types of adaptations: Structural Changes in the structure of body parts Physiological Changes in an organism’s metabolic processes

Structural Adaptations Can be used as defense mechanisms Mimicry A structural adaptation that provides protection for an organism by copying the appearance of another, more threatening, species Camouflage A structural adaptation that enables an organism to blend in with its surroundings Non-poisonous king snakes mimic poisonous coral snakes. Katydids have camouflage to look like leaves.

Physiological Adaptations Anti-biotic implications Individual bacteria in a population show variation Some bacteria possess a gene that makes them resistant to some antibiotic When the population is exposed to the antibiotic, some individuals die, but resistant bacteria survive Resistant bacteria survive and reproduce In time, the entire population is resistant to a certain antibiotic “Why does Evolution matter NOW?” http://www.pbs.org/wgbh/evolution/educators/lessons/lesson6/act1notes.html “The Evolution of Antibiotic Resistance” http://www.pbs.org/wgbh/evolution/educators/lessons/lesson6/act1.html

“Why does Evolution matter NOW. ” Video Questions http://www. pbs Why is the Russian prison system considered to be "ground zero" in the fight against TB? What is responsible for the evolution of TB strains that are resistant to multiple drugs? How does the misuse of antibiotics affect the evolution of disease-causing bacteria? Use the theory of natural selection to explain the growing resistance to antibiotics. Why should we care about a resistant strain of TB in Russia?

Evidence for Evolution Fossils can show evolutionary changes over time Anatomical structure indicate evolutionary relationship Analogous structures show similarity in structure based on adaptation for the same function, not common descent. Functionless structures indicate evolutionary pathways Seemingly functionless parts are called vestigial organs or structures. With all of the pain, time, and money that are put into dealing with wisdom teeth, humans have become just a little more than tired of these remnants from their large jawed ancestors. But regardless of how much they are despised, the wisdom teeth remain, and force their way into mouths regardless of the pain inflicted. There are two possible reasons why the wisdom teeth have become vestigial. The first is that the human jaw has become smaller than its ancestors’ and the wisdom teeth are trying to grow into a jaw that is much too small. The second reason may have to do with dental hygiene. A few thousand years ago, it might be common for an 18 year old man to have lost several, probably most, of his teeth, and the incoming wisdom teeth would prove useful. Now that humans brush their teeth twice a day, it’s possible to keep one’s teeth for a lifetime. The drawback is that the wisdom teeth still want to come in, and when they do, they usually need to be extracted to prevent any serious pain.

Evidence for Evolution Embryological development shows evolution from a common ancestor Structures that are embryologically similar, but have different functions, are called homologous structures. Genetic comparisons may reveal hidden relationships. Amino acid sequences are similar in related organisms!

Jean Baptiste Lamarck French Biologist Believed in SPONTANEOUS GENERATION Believed that living things evolved in a continually upward direction, from dead matter, through simple to more complex forms, toward perfection Believed that organisms altered their behavior in response to an environmental change; these changes caused modification to their organs & internal structure. He further believed that these modifications were inherited by the organism’s offspring Didn’t believe that species died out in extinctions, but instead they changed into other species