"nothing in biology makes sense except in the light of evolution” ~Theodosius Dobzhansky ( ) Photo by “davemee” flickr creative commons Chapter 16

In science, theories are statements or models that have been tested and confirmed many times.

In science, the term "Theory" does not express doubt. They explain a wide variety of data and observations They can be used to make predictions They are not absolute, can be changed as new evidence is found

Why do so many different animals have the same structures, the arm bones in a human are the same bones as a flipper in a whale? Why is the sequence of DNA very similar in some groups of organisms but not in others? Why do the embryos of animals look very similar at an early stage?

Photo courtesy of Swamibu, Flickr Creative Commons

Charles Darwin developed the THEORY OF EVOLUTION BY NATURAL SELECTION which explained how organisms changed over time (ADAPTED)

Darwin was a naturalist (what we today call biologists) He traveled the world and made observations and sketches of many species His most famous travels were aboard the H.M.S. Beagle where he traveled to the Galapagos Islands

Marine Iguana, photo courtesy of mtchm, flickr creative commons Blue-footed booby, photo courtesy of stirwise, flickr creative commons

Giant tortoise, photo courtesy of Planetgordon, flickr creative commons Finch, photo courtesy of stirwise, flickr, creative commons

Darwin noted that there existed many finches on the islands, but while they had similarities, each was adapted to eating a particular type of island food He concluded that the finches all came from one ancestral species and evolved into many new species Cactus finch, photo courtesy of zrim, flickr creative commons

Darwin published this work to explain the variety of species that exist on the planet He proposed the “Theory of Evolution by Natural Selection ”

1. Variation exists among individuals in a species. 2. Individuals will compete for resources (food, mates, and space) 3. Competition would lead to the death of some individuals while others would survive 4. Individuals that had advantageous variations are more likely to survive and reproduce.

This process came to be known as Natural Selection The favorable variations are called Adaptations

Say in a species of blob….there exists blobs of all shapes and sizes (variation) Blobs eat the little purple organisms that live underground and on the surface.

During a particularly hot year, food became less abundant (competition), blobs that had the ability to dig into the soil to get food had a better chance of survival. Many blobs died that year…….

The ones that survived mated and passed their genes to the next generation. (reproduction)

The next generation had move blobs with the pointed noses. That is NATURAL SELECTION. 1. Variation 2. Competition 3. Survival 4. Reproduction

Lamarke's Theory of Acquired Characteristics Some thought that you would gain or lose features if you overused or didn't use them, PROVEN TO BE WRONG! Photo courtesy of ucumari, creative commons, flickr

The who’s who of Evolution Many scientists believed that the Earth was only a few thousand years old in Darwin's time Geology was a relatively new science and was just starting to show evidence of the real age of the earth James Hutton and Charles Lyell formed important hypothesis based on this information They concluded that the Earth is extremely old and that processes that changed the Earth in the past are the same processes we see presently.

Hutton was one of the first to see the connection between geological time and geological processes like mountains and valleys Lyell connected the idea that since the Earth was so much older then people thought the geological formations like canyons where actually due to the flow of the river though it eroding the area for thousands of years

Direct observation of species change 1. Bacteria become resistant to antibiotics 2. Wolves were bred over many generations to become dogs (artificial selection) and then bred further to create a variety of breeds

Population Growth Thomas Malthus was an English economist who first recorded the population growth issue He noted that more people where being born then where dying and this lead to over crowding Malthus recognized that these conditions would slow down population growth in the end through war, disease, and starvation 

16.3 Darwin Makes His Case Darwin waits 20 years before he publishes his findings from his trip on the HMS Beagle Alfred Russell Wallace writes and essay that Darwin sees that is VERY similar to his work but done based on his work in Malaysia. Darwin finally publishes his theory in 1858 He call’s it “On the Origin of Species” and he presents it to the scientific board This is his Theory of Evolution based on Natural Selection It focuses on an organisms fitness, meaning which organism is best adapted for survival and reproduction in a given environment

Example

The Age of Earth and Fossils Darwin realized that that natural selection would not be easy to prove because it takes a very long time to prove that his theory is true. Today geologists use radioactivity to find the age of rock and fossils. Darwin would be pleased to know that their work supports his theory. When Darwin was alive he discovered many fossils that changed over time however, there were not enough fossils to show clearly how modern species had descended from their ancestors. Today there have been hundreds of new fossil discoveries that show and support how many modern species have evolved from older species.

Fossil Evidence Shows numbers extinct animals Shows similarities between extinct animals and animals that are alive today The earth’s layers show a time scale of species and when they appeared on earth (and when they died out)

Dinosaurs have always fascinated us, movies such as Jurassic Park capitalize on that fascination. How do we know what dinosaurs looked like? We create a picture based on the bones we find (fossils) and use modern reptiles to guess at their texture and skin color.

Evidence of Evolution Darwin used Biogeography to support his theory. Biogeography is the study of where organisms live and where their ancestors lived in the past. 2 important patterns: 1 closely related organisms that live in different environments often show great differences. 2. Distantly related organisms that live in similar environments are often similar

Homologous structures – these are parts of the body that are similar, but have different functions ex. The flippers of whales, and the wings of birds All forelimbs of vertebrates have the same pattern of bones Common ancestry

Analogous Structures There are times that body parts share a common function however, they are not structurally related. These structures are ANALOGOUS STRUCTURES. The wings of bees, birds, and bats are called analogous. Analogous structures do not show common descent.

Vestigial Organs – these are organs or parts that seem to have no function Examples Whales have pelvic bones that do not attach to legs You have an appendix that seemingly does nothing for us at this point

Biochemistry and DNA When comparing the DNA of one species to another, more similarities are found in species that are more closely related. Lion photo credit: ucumari Tiger photo credit: digitalART2

Genetics and Molecular Biology Darwin did not truly understand how heredity worked. Since his time, biologists have learned a great deal about heredity. COMMON GENETIC CODE – All living things use DNA and RNA to make proteins and to pass on genetic information. HOMOLOGUS MOLECULES – Biologists have found many homologous molecules.

Embryological Development Embryos of different species develop in almost identical ways. Human fetus at 8 weeks

Creationism, sometimes referred to as “creation science” or “intelligent design” is the belief that organisms were placed on this earth by a divine being (God). It is NOT a theory because it does not follow scientific principles (theories require evidence, and must be based on NATURAL PHENOMENON)

Finding gaps in our knowledge about evolution is a normal part of the scientific process, the existence of these “gaps” and questions does not qualify as evidence that an alternative theory must be correct Beliefs are yours to hold on to based on your own family’s teachings my job is to teach you the science