16.1-16.4 / 17.1-17.2/19.2

Darwin’s Voyage of Discovery

  Born in England in 1809 and grew up in a time when scientific views were beginning to shift.

Sailed on the HMS Beagle for a 5 year journey.

  Goal was to map South America and collect specimens.

This trip led him to develop his theory of biological evolution which explains how modern

organisms evolved over long periods of time through descent from common ancestors.

 As Darwin traveled he noticed three patterns of biological diversity:  Species vary globally  Species vary locally  Species vary over time

 Noticed similar flightless birds (Rhae, Ostrich, and Emu) each living in similar habitats in three different continents. These three are now categorized under the term Ratite.

 However there were species that were not found in the same habitats across the globe (kangaroos, rabbits, and other species).

  Noticed that tortoises shell shape varied based on which Galapagos Island they lived on.

Noticed that in South America that different species of Rheas lived in drastically different conditions of grasslands.

 Noticed there was a wide variety of small brown bird on the Galapagos Islands as well. He would later recognize them to be finches and the variation in their beaks would be a basis for a major set of evidence of change over time. Populations evolved to better suit their eating/tool needs.

 Darwin was an avid fossil collector and he noticed that some fossils of ancient / extinct animals were similar to living species.

 Example: The Glyptodont (extinct) at 3m in length and the Armadillo at 0.5m in length both are versions of each other and are found in the same area. Made him wonder what is the connection?

 Darwin’s theory of Evolution arose from his careful documentation of species on his travels and how there were species of organisms that were similar to others in the world but that particular species was found NO WHERE ELSE. The evidence suggested that species are not fixed and that they could change by some natural process called evolution.

Ideas that shaped Darwin’s thinking

 In Darwin’s day though evidence was being discovered and ideas were changing many Europeans believed that Earth was only a few thousand years old. Many scientists along with Darwin played important roles in bringing evidence to light.

   He was a geologist so he studied geologic structures (mountains, valleys, layers of rocks, etc.) Discovered connections between geologic processes and geologic features. How is it possible that all the geologic features could have possibly formed in thousands of years? Mountains, valleys, rivers, uplift, tilting, etc….

  Found it would take a long period of time for certain formations to form and created a concept called deep time.

The concept of deep time said that our Earth’s history is so long that our human minds cannot properly imagine it.

 Published his work in 1785: Theory of the

Earth; or an Investigation of the Laws observable in the Composition, Dissolution, and Restoration of Land upon the Globe.

 He broke all the molds by proposing that the center of the earth was hot/ molten which helped to create new rock and form processes on land.

 His ideas were not accepted readily by many groups. (Neptunists, Catastrophists, etc.)

  Discovered that the geological process going on were always going through regular cycles of destruction and rebuilding. Is famous for the idea of uniformitarianism.

 He was insistent that the processes for the Earth are uniform throughout history and what occurred in the past will keep occurring into the future.

 Published his work in 1830:

Principles of Geology

 The combination of Hutton and Lyell’s work created what is now known as the rock cycle.

  Darwin read his book and connected Lyell’s ideas of geological processes to those occurring in things that are living.

Darwin experienced an earthquake which displaced sea life over 3m and showed him how the geology can change and the organisms with it.

 He was suggesting the change of species before Charles Darwin was born.

 Thought all organisms strived to become more perfect.

Two main ideas:  He suggested the organisms could change during their lifetimes by selectively using or not using various parts of their bodies.

Two main ideas:  He also suggested that individuals could then pass these acquired traits on to their offspring, enabling species to change over time.

 Ex: By not using features (ex: wings) they would over time become smaller and useless. Flying birds would then would be land or water bound.

 Ex: If a bird needed longer legs to wade in deep water they could make an effort to stretch them to make them longer.

Evaluating his thinking  Organisms don’t have the drive to be perfect. They just want to survive!

 Evolution does not mean that a species becomes “better” and it doesn’t progress in a predetermined direction.

 Also traits acquired during ones lifetime ( a broken wing which becomes useless) cannot be passed on to offspring.

 Published his work in 1809 the year that Darwin was born.

 While the basis of many of his ideas of evolution were wrong his thought process was true in explaining that there was a link between environment and body structures. This paved the way for future scientists like Darwin.

  He noted that when human populations grew out of control that there was a limitation of space/resources and it required there be a population of people in poverty who would not have access to resources. Only the strongest were surviving because if left unchecked there would not be enough living space for everyone and definitely not enough resources

 He claimed their were two types of checks that hold populations within resource limits:  Positive Checks (raise the death rate) ▪ Ex: famine, war, disease  Preventative Checks (lower the birth rate) ▪ Ex: birth control, postponing marriage, celibacy, using moral constraint to not have children until you could support them.

 Though he was deemed to be insensitive to the poor he merely was looking at methods by which to reduce the immense amount of poverty as seen in large cities (particularly England).

   Darwin applied this to living organisms as well. Organisms like trees and oysters can produce thousands to millions of eggs/seeds per year.

What if all those seeds/eggs survived to produce that organism? They would overrun the world so there needs to be some level of balance of the population.

 In this type of selection nature provides the variations, and humans select (and breed) those they find useful.

 Darwin did this with pigeons and was able to create what he called fancy pigeons.

 Where else do we see artificial selection?  Dogs, horses, farm animals, etc. It is everywhere around us!

 This led Darwin to think about natural variation in the wild and how it provided the raw materials for evolution.

 On p. 459 there is a great timeline of scientists

Darwin Presents His Case

Based on his experiences in travel, and research of other scientists’ data, he created a draft of his thoughts on natural selection but he waited 20 years to publish it! Why so long?  Because he saw the backlash that other scientists received for their ideas so he decided to wait and gather more evidence to support his ideas. What finally forced him to publish his work on evolution (On the Origin of Species)?

 Another scientists, Alfred Russell Wallace, was about to publish a book with the same thoughts as Darwin. He didn’t want to lose his credit so he was forced to publish early.

 Based on reading Malthus he explains that if there are more organisms born then the environment can provide space/food for some will live while others will die. This brings up the important question of who survives and who doesn’t? Darwin states that those overall suited for their environment (the fittest) will survive.

 The more fertile the environment the more organisms it can hold (Harsh desert vs. thriving jungle)

  Due to sexual reproduction all offspring will be genetically different and will provide genetic variations into a population. Those variants that are better suited for their environment will survive.

Those that survive will then pass on those better suited traits onto their offspring.

 Any heritable characteristic that increases an organism’s ability to survive and reproduce in its environment is called an adaptation; coloration, claws, wings, camouflage, mimicry, etc

  Darwin used the term “fitness” to give a level to how well suited an organism was for its environment. Those with high fitness are well suited to their environment and can survive and reproduce at high rates.

 However those with low fitness are not suited to their environment and reproduce at very low levels. (few offspring is bad!)

 Question: If an organism produces many offspring, but none of them reach maturity, do you think the organism has high or low fitness? Explain why.  Answer: Low fitness because it needs to be able to reproduce and have those offspring survive to keep the species lineage going.

 He summed up all of this with his term survival of the fittest where survival means having the ability to pass on your genetics and adaptations to future generations.

  In natural selection the environment influences fitness.

Natural selection occurs when:  More individuals are born than can survive.

 There is natural heritable variation.

 There is variable fitness among individuals.

  Those with the highest fitness will adapt and survive and those with the lowest fitness will die off.

Natural selection only works for heritable traits. Note that this is not the ONLY mechanism driving evolution… more to come!

  He proposed that over time new species form that are modified forms of their descendents.

He used evolutionary trees to show how different species came from one original descendent. According to this principle all organisms are descended from ancient common ancestors.

Evidence of Evolution

 Evolution = fact  The mechanism of how organisms change over time = theory (it is testable/falsifiable)  Also evolution is not about perfection it is about survival

 Biogeography is the study of where organisms live now and where they lived in the past.

 The patterns formed in the distribution of living and extinct species tell us how modern organisms evolved from their ancestors. (movement, environment, etc.)

 Many newly discovered fossils, are filling in the fossil record, and helping to complete the tracing of evolution of living species from extinct ancestors.

  A clue to common descent from an ancient ancestor.

Common structure, but NOT common function.

  This is synonymous (similar in definition to) divergent evolution.

Divergent evolution is the accumulation of differences between groups which can lead to the formation of new species, usually a result of diffusion of the same species to different and isolated environments which blocks the gene flow among the distinct populations allowing differentiated fixation of characteristics through genetic drift and natural selection.

  This is not a form of common descent.

Body parts that share common function, but NOT structure.

 Ex: wing of a bee vs. wing of a bird. Both fly, but they are not built nearly the same. Both acquired the wing to help with flight.

  This is synonymous with convergent evolution.

Convergent evolution describes the acquisition of the same biological trait in unrelated lineages.

 Structures that are passed from generation to generation but have no functional use.

  Why do organisms keep these if they are not of use?

Scientists are not 100% sure but the current theory is that the presence of the structure does not hurt the organisms fitness level for survival and therefore natural selection doesn’t act quickly to eliminate it.

 Study of looking at embryos!

  In this picture the top row is the actual organism where the bottom row is an artistic rendering pointing out significant features. How are the different pictures across the top similar? How are they different?

Do you think they all come from the same lineage of organism? Why or why not?

 From left to right they are the following organisms: Salamander, Human, Rabbit, Chicken, and Fish

  The strongest evidence for descending from a common ancestor is based on genetics.

The Human Genome Project has coded the genetics of a vast number of organisms and guess what? We are all VERY similar.

 To the point where the genetic code is nearly identical in almost all organisms (bacteria, yeasts, plants, fungi, and animals). There must have been a common ancestor at one point in order for this to happen.

 Evolution, in genetic terms, involves a change in the frequency of alleles in a POPULATION over time.

 If the frequency of an allele is increasing or decreasing it means that a population is evolving. Judged by looking at the gene pool of populations genes.

 Natural Selection happens to individuals, but the changes that it causes in the allele frequency shows up in the population as evolution.

 IMPORTANT: The smallest unit that can evolve is a population, NOT individuals.

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Mutations (change in DNA sequence) Genetic Recombination in Sexual Reproduction (passing from parents to offspring) Lateral Gene Transfer (important for single celled organisms where they swap genes through plasmids)

  Single Gene traits are much more simple as they only involve one gene and can lead to allele frequency changes faster.

Polygenic Traits require more than one gene and therefore take a much longer time to affect the allele frequency.

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Stabilizing

selection- natural selection that favors the average individuals in a population. (Average birth mass of baby survives!)  In this the extremes will die out.

 Individuals with either extreme of a trait’s variation are selected for survival.  The average phenotype tends to be eliminated. (small and large beak size survives if small/large seeds are in abundance)

 natural selection that favors one of the extreme variations. (woodpecker with longer beak survives since it can get food easier from tree)

 Geographic Isolation: physical barriers may prevent this reproduction from happening. A volcano eruption or a river may isolate a species. Therefore, a new species may evolve. These new organisms adapt to their new environment and start their own gene pools.

 Reproductive Isolation: Different mating times and the ability to fertilize an organism of the same species could also result in speciation. NOTE:

speciation means to form a new species.

 Nondisjunction: Changes in chromosome number can also cause speciation, which is seen in wheat and apples.

 Speciation can occur quickly or slowly  Gradualism- species originate through a gradual change of adaptations slowly.

  Punctuated equilibrium- speciation occurs quickly in rapid bursts due to changes in geography, climate, predators.

*****Both views are supported by fossil evidence*****

 Background extinction is coined “business as usual” extinction because there is a natural competition of evolution and survival over a longer period of time.

 Whereas Mass extinction is a relatively rapid extinction where entire ecosystems vanish, whole food webs collapse, species go extinct due to food loss, and the process of natural selection just cannot compensate quickly enough.

 What can cause these extinctions?  Asteroids, global climate change, volcanoes, moving continents, and changing sea levels.

 After this many species go extinct which leaves space for other species to take over. This rebuilding can take anywhere from 5 to 10 million years.

 This is the process by which a single species or a small group of species evolve over a relatively short period of time into several different forms that live in different ways.  This is what Darwin discovered in the finches on Galapagos Island.

 After the dinosaurs went extinct an adaptive radiation occurred which brought a large variety of organisms into the population.

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When two different species are so closely linked that they evolve together.

Ex. of a GOOD relationship: Flowers and Pollinators  Flowers need to pollinate and pollinators (ex: bees, moths, etc.) want the nectar inside the flower. Pollinators will adapt to best retrieve the nectar and in turn by more pollinators being able to get the nectar the flower will pollinate more often.

Ex. of a BAD relationship: Plants and Herbivores  Herbivores like to eat plants. Over time plants have evolved bad-tasting or poisonous compounds that keep herbivores from eating them. In response the herbivores will adapt to be able to be resistant to such poisons (or even be able to store it in their tissues to ward off predators). And so the cycle continues.

Ex. of a BAD relationship: Plants and Herbivores  NOTE: this relationship that has caused plants to be so poisonous has created some of the most powerful natural poisons used by humans.