Unit 9 Chapter 13: The Theory of Evolution. SECTION 1. Charles Darwin and the Theory of Natural Selection. Darwin’s Voyage on the H.M.S. Beagle.
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SECTION 1 Charles Darwin and the Theory of Natural Selection
Darwin’s Voyage on the H.M.S. Beagle In 1831, Charles Darwinset sail from England aboard the H.M.S. Beagle on a voyage that primarily visited areas located in the southern hemisphere. Darwin collected numerous plant and animal specimens from each location he visited. He studied the specimens, read the latest scientific publications, and drew pictures and recorded his observations and thoughts in notebooks.
Darwin’s Voyage in the Southern Hemisphere
Darwin’s Book: On the Origin of Species by Means of Natural Selection • Before Darwin proposed his theory on evolution, scientists thought that each species was a divine creation that existed, unchanging, as it was originally created. • Darwin’s evidence led him to propose a revolutionary hypothesis pertaining to the way life changes over time. • This hypothesis has now become known as the theory of evolution. Darwin presented his theory in his book, On the Origin of Species By Means of Natural Selection, that was published in 1859.
Darwin and the Galapagos Islands Darwin observed that the Galápagos Islands were in close proximity to the mainland of South America, but had very different climates and differences in vegetation. He also observed that the characteristics of many animals and plants varied noticeably among the different islands.
Darwin’s Case:Variation Within Species • Members within a species vary from one another in important ways. • At the time, variations were thought to be unimportant, minor defects. • Darwin argued that this variation was significant and very important.
Darwin’s Case: The Struggle For Existence Darwin realized that high birth rates and a shortage of life's basic resources (food, water, and shelter) inevitably force organisms to compete for resources. Competition, both within and among species, exists in almost all natural environments.
Darwin’s Case: The Struggle For Existence
Darwin’s Case: Natural Selection and Evolution • Darwin made a key association: Individuals that have physical or behavioral traits that better suit their environment are more likely to survive and will reproduce more successfully that those that do not have such traits. • Over time, the number of individuals that carry favorable characteristics that are also inherited will increase in a population. • As the favorable characteristics increase in a population, the nature of the population will change – a process called evolution. • Darwin called this differential rate of reproduction natural selection.
Darwin’s Case: Natural Selection and Evolution • According to Darwin, natural selection is a process resulting in the survival of those individuals from a population of animals or plants that are best adapted to the prevailing environmental conditions. • The survivors tend to produce more offspring than those less well adapted, so that the characteristics of the population change over time, thus accounting for the process of evolution.
Putting it all Together…Survival of the Fittest Fitness is the ability of an organism to survive and reproduce in its specific environment. Darwin proposed that fitness is the result of adaptations. An adaptation is any inherited characteristic that increases an organism's chance of survival.
Natural Selection:Descent with Modification Natural selection yields organisms that display different structures, establish different niches, and may occupy different habitats. Every living species has descended, with changes, from other species over time. Darwin referred to this principle as descent with modification.
Natural Selection in Action Darwin wondered if animals living on different islands had once been members of the same species. These separate species would have evolved from an original South American ancestor species. His observations of finches, tortoises, iguanas, and other animals supported his hypothesis.
Darwin later suggested that the simplest explanation for the similarities between the species on the islands with the species on the mainland was that the ancestors of the Galapagos species migrated to the islands from South American long ago and changed after they arrived. • Alfred Wallace, an English naturalist, wrote an essay and sent it to Darwin in 1858 describing his theory of evolution, which was very much like Darwin’s theory.
“On The Origin of Species by Means of Natural Selection” • Darwin’s book, ”On The Origin of Species by Means of Natural Selection” appeared in November of 1859 after almost thirty years of work and research. • Darwin’s theory of evolution by natural selection is supported by four major points: • 1.) Inherited variations exist within the genes of every population or species as a result of random mutation and translation errors. • 2.) In a particular environment, some individuals of a population or species are better suited to survive as a result of variations, and thus have more offspring (natural selection).
“On The Origin of Species by Means of Natural Selection” • 3.) Over time, the traits that make certain individuals of a population able to survive and reproduce tend to spread in that population. • 4.) There is overwhelming evidence from fossils and many other sources that living species evolved from organisms that are now extinct. • Many people were upset by Darwin’s theories, especially the Roman Catholic Church, because his theories differed from the Church’s teachings of creationism. • Today, new discoveries in the area of genetics has given scientists new insight about how natural selection brings about the evolution of species.
Eastern and Western Meadowlarks can normally only be distinguished by their calls.
An Example of Natural Selection:Industry and the Peppered Moth • Coal burning during the Industrial Revolution in the late 1890s and early 1900s caused the trees in nearby forests to turn dark with soot. • Within a short period of time, the peppered moth began to change in appearance. • http://www.techapps.net/interactives/pepperMoths.swf
Change Within Populations • According to natural selection, the traits of individuals who are more suited to their environment will be passed on and become more common in each new generation. • Scientists now know that genes are responsible for inherited traits. • Natural selection causes the frequencyof certain alleles in a population to increase or decrease over time. • Mutations and the recombination of alleles that occurs during sexual reproduction provide endless sources of new variations for natural selection to act upon.
Reproductive Isolation • The environment differs from place to place, so populations of the same species living in different locations tend to evolve in different directions. • Reproductive isolation is the condition in which two populations of the same species do not breed with one another because of geographic separation, a difference in mating periods, or other barriers to reproduction. • Over time, the two isolated populations of the same species become so different they can no longer breed with one another, and become two separate species.
The Kalibab squirrel (top) lives on the North Rim of the Grand Canyon. • The Abert squirrel (bottom) lives on the South Rim of the Grand Canyon. • Because the two species have been so isolated from one another, they have become different enough that some biologists consider them to be separate species.
The Tempo of Evolution • Gradualism is the term used to describe the model of evolution in which gradual change over a long period of time leads to a species formation. • American biologists Jay Gould and Niles Eldredge suggested that species may stay unchanged for long periods of time, and then major environmental changes in the past caused evolution to occur in spurts. They called their theory punctuated evolution. • Punctuated evolution is the model of evolution that suggests that periods of rapid change in species are separated by periods of little or no change. The evolution of the species is “punctuated” or broken up.
SECTION 2 Evidence of Evolution
Evidence of Evolution:The Fossil Record • Fossils provide an actual record of Earth’s past life-forms. Change over time can be seen in the fossil record. Fossilized species found in older rocks are different from those found in newer rocks. • Darwin predicted that intermediate forms between the great groups of organisms would eventually be found in fossils. • Based on a large body of supporting evidence, most scientists today agree that the Earth is about 4.5 billion years old and that organisms living today share common ancestry with earlier life-forms.
Fossils of archaeopteryx, a reptilian-like bird that lived over 150 million years ago, were found in Germany in the 1860s. The fossils seemed to support Darwin’s theory of intermediate species.
In the 1930s, Alfred Wegener proposed the theory of continental drift. He theorized that the continents were once connected over 200 million years ago in one large land mass he called Pangaea. Wegner believed that slowly, over time, the continents drifted to their current locations. This was later found to be caused by convection currents in the magma found in the Earth’s mantle. Wegener based his theory on evidence from fossils that had similarities in structure, but were found on separate continents that were separated by great distances. Wegner theorized that the organisms must have developed in areas where the continents were once joined together, and then were separated from each other over time.
Anatomy and Development • Some structures in organisms, such as bones, become reduced in size and either have no use or have a less important function that they do in other related organisms. • Think about the dew claw on a dog or a cat – what purpose do these claws serve now? • These structures are known as vestigial structures and are considered to be evidence of an organism’s evolutionary past.
Vestigial Structures, Homologous Structures, and Analogous Structures • A vestigial structureis a structure in an organism that is reduced in size and function and that may have been complete and functional in the organism’s ancestors. • An example of a vestigial structure would be the dew claw of a cat or dog. • Homologous structures are structures that share a common ancestry – a similar structure in two organisms that can be found in the common ancestor of the organism.
Vestigial Structures, Homologous Structures, and Analogous Structures • The forelimbs of humans and bats are examples of homologous structures. • Although they are used differently, the basic skeletal structure is the same and they are derived from the same embryonic origin. • Their similarity in this regard could indicate a likely evolution from a common ancestor.
Vestigial Structures, Homologous Structures, and Analogous Structures • Analogous structures pertain to the various structures in different species having the same appearance, structure or function, but have evolved separately, and thus do notshare a common ancestor. Examples of analogous structures include: • wings of insects and birds used for flying • jointed legs of insects and vertebrates that are used for locomotion • fins of fish and flippers of whales (mammals)
Anatomy and Development • Most scientists believe that the evolutionary history of organisms can also be seen in the development of embryos. • At some time in their development, all vertebrate embryos have a tail, buds that become limbs, and pharyngeal pouches which become gills in fish and amphibians. • In humans, the tail disappears during fetal development, and pharyngeal pouches develop into structures in the throat.
early reptile pterosaur chicken bat porpoise penguin human 1 2 3 4 5 1 2 3 4 1 2 3 1 2 1 3 4 5 2 4 3 5 2 3 1 2 3 4 5
inside lobed fin; bony or cartilaginous structures (orange) undergoingmodification limb bones of an earlyamphibian