(Chapters 16-17)
Darwin presented evidence that evolution happens and offered an explanation of how it happens. Evolution the process by which species change over time Theory a broad explanation that has been scientifically tested and supported Keeps developing and expanding as more evidence is uncovered Most of Darwin s theory remains scientifically supported to this day. Charles Darwin was born Feb. 12, 1809 the same day as Abraham Lincoln.
Darwin wanted to understand the biodiversity on Earth. Biodiversity the variety of living things
Darwin was intrigued that so many plants and animals seemed so well adapted to their environments. Darwin was also impressed by the many ways that organisms survived and reproduced. Organisms that lived in similar habitats in different parts of the world were very different.
Species vary globally Darwin noticed that different, yet ecologically similar, animal species inhabited separated, but ecologically similar, habitats around the globe. Darwin visited a wide range of habitats on the continents of South America, Australia, and Africa and he found different types of flightless ground-dwelling birds on each continent. South America rheas; Africa ostriches; Australia emus
Species vary globally Rabbits and other animals found in the European grasslands were missing from the grasslands of South America and Australia. Australia was home to kangaroos and other animals that aren t found anywhere else.
After finishing college, Darwin sailed with the crew of the HMS Beagle from 1831-1836. As the naturalist on the ship, Darwin collected fossils and living specimen and made thousands of observations about the organisms and their environments.
The Galápagos Islands volcanic islands in the Pacific Ocean near Ecuador Many of the plants and animals were similar but not identical to those found in South America.
Some of the fossils that Darwin collected looked similar to species living today.
Giant Ground Sloth Megatherium
Some of the fossils that Darwin found looked nothing like any thing he had ever seen. Darwin s questions Why had so many species disappeared? How were they related to living species?
Although the Galapagos Islands are very close together, they have very different climates. The plants and animals of each island were adapted to that specific environment.
Tortoises The shape of tortoise shells changed depending on the type of food available on the island.
Finches After collecting many species of this bird, Darwin noticed the size and shape of the beak were different depending on the type of food available for the finch to eat.
Marine Iguanas Reptiles that forage underwater for food but live on land. Planet Earth 2 Clip
Darwin realized that variation exists in every population of organisms. Some plants produce large fruit than others. Some cows produce more/better milk than others. Some horses run faster than others.
Breeders were taking advantage of the variation in traits within a species. Select parents with desired traits to produce offspring with those traits. Darwin called this process artificial selection because humans were selecting traits. (AKA selective breeding) Humans choosing mates for organisms to produce desired traits in offspring.
Darwin realized that humans were driving the evolution of many plant and animal species.
In Darwin s time (late 1800 s), most people believed that each species was created once and stayed the same forever. So, why do we have fossils of organisms that are no longer here? Most people believed that the Earth and living things did not change. What about volcanoes, earthquakes, floods, etc.?
Jean Baptiste Lamarck s Hypotheses (1809) Organisms change over time. All species are the descendants of the species that came before them. All organisms are trying to be more complex and more perfect. Traits pass to offspring based on use and disuse (use it or lose it). Offspring can inherit acquired traits (like larger, stronger muscles)
Thomas Malthus (1789) Observed that the human population was increasing faster than the food supply. Noted that it could not continue this way humans would eventually die from disease, war, or famine. Darwin applied this idea to all populations. Populations produce more offspring than its environment can support, therefore, many will die.
Georges Curvier Argued that fossils in rock layers showed differences in species throughout time and many species from the past differed from those in the present (which implies change). James Hutton (1795) and Charles Lyell (1830) Geological processes (like erosion) work gradually and constantly. Darwin concluded that the Earth is old enough for species to evolve gradually.
Darwin waited to publish his ideas on evolution because he knew that these ideas were revolutionary and would challenge the fundamental scientific beliefs of the day. In 1858, Darwin received a letter from Alfred Wallace, a fellow scientist that was doing similar studies in Malaysia. Alfred Wallace s essay outlined Darwin s idea of evolution by natural selection.
Darwin published his book, On the Origin of Species by means of Natural Selection in 1859. Darwin s book explained the process of evolution and provided evidence that evolution has been taking place for millions of years and continues to happen today.
If you are a pine tree, a fly, or a squirrel, what is your goal in life? As a human, what is your ultimate goal in life? The ultimate goal of every organism is to SURVIVE and REPRODUCE
Struggle for Existence Members of a species compete regularly to obtain food, living space, mates, etc. A key factor in the struggle is how well suited an organism is to its environment.
Fitness - the ability of an organism to survive AND reproduce Fitness is the result of adaptations. Adaptation any trait that increase an organism s chance of survival or reproduction.
Camouflage an adaptation that allows organisms to blend with the environment to become less visible to predators or prey.
Mimicry an adaptation where one species resembles another species Example A harmless snake looks that looks like a harmful snake will be avoided.
Better adapted individuals survive and reproduce more offspring (higher fitness) Less adapted individuals have less chance of survival and reproduction (lower fitness)
Natural selection Only certain individuals in a population will produce offspring The selected traits increase in the population causing the entire population to evolve not the individual. An individual cannot make itself adapt to the environment: its all in the genes. Evolution is a gradual process of adaptation.
Descent with Modification Each living species has descended, with changes, from other species over time. Descend to come from
Kings of Camouflage: Cuttlefish (21:20-29:46) Octopus Camouflage
The Fossil Record all the traces of organisms that lived in the past Comparing fossils and living organisms reveals a pattern of gradual change from the past to present. The fossil record will never be complete because the conditions necessary to create fossils are rare.
Biogeography the study of the locations of organisms around the world Scientists have found the movement of landforms in Earth s past help explain patterns in the type and location of both living and fossil organisms. http://www.youtube.com/watch?v=wauk94adxpa&feature=related
Anatomy comparing the body structures of different species Closely related species will have similar structures. Homologous Analogous Vestigal
Homologous structures structures that have developed from the same tissues in the embryo (may not have the same function) Homologous structures result from common genes
Analogous structures similarities that evolve in unrelated groups because of similar lifestyles or habitats due to convergent evolution. Example Birds, bats, and bugs all have wings that are used to fly but each evolved separately. The structure of the wings and the genes that produce them are different.
Vestigial Structures body parts that do not seem to play a role in an organism s life functions (evolutionary leftover) Example the human appendix has no apparent function while rats and other rodents have an appendix that aids in digestion Example whales and snakes have a pelvis and femur
Embryology comparing the embryonic development of organisms to look for similar patterns and features Not identical but similar The closer the development pattern the closer the evolutionary relationship
Biochemistry comparing the genes of different species Can compare DNA sequences or amino acid sequences Similar sequences may imply relatedness Compare the sequences. Which organisms are more closely related? Human ACT GAG TCG CCT ACG Monkey ACT GCG TCG CGT ACG Cow ACT GGG TCA CGT AGC
Strengths Supported by a lot of evidence. Logical and testable Still stands today Weaknesses Darwin knew very little about genetics. Mendel was just starting to count peas (Mendel s work was not published until 1900).