CK-12 Biology I - Honors
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Australopithecus, perhaps the earliest, upright hominid, appeared during the Pliocene. Global cooling and glaciation led to a drop in sea level, exposing two land bridges which allowed important animal migrations.
Cycles of glaciation stressed Pleistocene animals and plants; some, like the woolly mammoth, adapted to cold and others, like Homo erectus, the dominant hominid, migrated throughout Africa, Europe, and Asia.
As the human population climbs above 6.6 billion, we may be causing a Sixth Extinction of life on Earth.
Review Questions
What major evolutionary steps followed the evolution of the first eukaryotic cell during the late Precambrian to set the stage for the “Cambrian explosion?”
List the global environmental factors which influenced the evolution of multicellular life.
Discuss and give examples of the relationships among the environmental factors you listed above. Include their major effects on the history of life.
Describe the conditions under which the dinosaurs emerged to dominate life on Earth, and identify the diversity of habitats and niches occupied by the dinosaurs during their “golden age.”
What famous example of coevolution began in earnest during the Cretaceous? Give two early examples.
Cite and evaluate the evidence for an “impact event” as the primary cause of the K-T extinction.
Analyze the emergence of mammals and birds as dominant land animals during the early Cenozoic.
How does the Cenozoic climate explain the emergence of grassland and tundra and their megafauna?
Give two examples of how land bridge formation can affect evolution.
Discuss the factors which are contributing to the current major extinction, and analyze your own response to E.O. Wilson’s description of the “Sixth Extinction.”
Further Reading / Supplemental Links
Mark Pagel, ed. The Oxford Encyclopedia of Evolution. New York: Oxford University Press, 2002.
Stephen Jay Gould, ed. The Book of Life: An Illustrated History of the Evolution of Life on Earth. New York: W.W. Norton, 1993.
Colleen Whitney, Kate Barton, David Smith, “The Paleontology Portal.” University of California Museum of Paleontology, Paleontological Society, Society of Vertebrate Paleontology, and US Geological Survey, 2003. Available on the Web at:
http://www.paleoportal.org/index.php
“Continental Drift Animation.” EduMedia-sciences, 2002-2007.Available on the Web at:
http://www.edumedia-sciences.com/a95_l2-continental-drift.html
Dave Smith, “Life Has a History – Level 2.” University of California Museum of Paleontology, 7/18/06. Available on the Web at:
http://www.ucmp.berkeley.edu/education/explorations/tours/intro/Intro5to12/tour1nav.php
David Ulansey, “The Current Mass Extinction.” David Ulansey, last updated 3 July 2007. Available on the Web at:
http://www.well.com/user/davidu/extinction.html
Lexi Krock, “The Missing Link: A Brief History of Life.” Nova Online, last updated February 2002. Available on the Web at:
http://www.pbs.org/wgbh/nova/link/history.html
Richard Cowen, “History of Life, 4th edition Updates, References and weblinks.” UC Davis Geology Department, 3 March 2006. Available on the Web at:
http://www-geology.ucdavis.edu/~cowen/HistoryofLife/
Roger Perkins, “The Virtual Fossil Museum: Fossils across Geologic Time and Evolution.” Available on the Web at:
http://www.fossilmuseum.net/index.htm
Roy Caldwell and David Lindberg, “Understanding Evolution.” University of California Museum of Paleontology, 2007. Available on the Web at:
http://evolution.berkeley.edu/
Vocabulary
Archaeopteryx
One of the most famous transition fossils; has characteristics of both reptiles and birds.
Cambrian explosion
The abrupt emergence of many new species during the Cambrian Period.
liverworts
Among the first true plants; colonized land during the Ordovician.
Jurassic Period
The golden age of the large dinosaurs which lived amidst warm, fern-and cycad-filled forests of pines, cedars, and yews.
Lucy
One of the most complete fossils of Australopithecus afarensis, a human relative also known for fossil footprints which establish an upright posture.
marsupials
One of the three major groups of mammals.
monotremes
One of the three major groups of mammals.
Pangaea
A single supercontinent formed from all the major land masses of Earth; formed during the Permian.
placentals
One of the three major groups of mammals.
trilobites
Common arthropods which were diverse and abundant during the Cambrian Period.
Points to Consider
The study of the history of life attempts to answer the age-old question: where did we humans come from? What are some of the answers our current knowledge gives us? What points are still missing?
To what extent has life itself influenced the history of life on Earth? Consider some specific effects certain kinds of life have had on climate, the atmosphere, and certain species.
At least some mammoth DNA has been preserved in permafrost. What do you think about the idea of re-creating animals such as the mammoth from the past – as fictionalized in Jurassic Park?
Do you think extinction plays an essential role in evolution? Is it a negative or positive role?
Do you judge the Sixth Extinction to be an important problem? Do you think it is significantly different from earlier extinctions?
Chapter 12: Evolutionary Theory
Lesson 12.1: Darwin and The Theory of Evolution
Lesson Objectives
Identify important ideas Darwin developed during the voyage of the Beagle, and give examples of his observations that supported those ideas.
Recognize that scientific theories and discoveries are seldom the work of just one individual.
Describe prevailing beliefs before Darwin about the origin of species and the age of the earth.
Evaluate Lamarck’s hypothesis about how species changed.
Analyze the impact of Lyell’s Principles of Geology on Darwin’s work.
Evaluate the influence of Malthus’ ideas about human population on Darwin’s thinking.
Discuss the relationship between Alfred Russel Wallace and Charles Darwin.
Describe the general ideas of Darwin’s Theory of Evolution.
Use Darwin’s reasoning to explain natural selection as the mechanism of evolution.
Explain how natural selection results in adaptation to environment.
Recognize the importance of variation to species survival.
Relate the idea of differential survival to the concept of natural selection.
Interpret the expression “descent with modification.”
Discuss the concept of “common ancestry.”
Show how Darwin’s theory provides a scientific explanation for the fossil record.
Interpret Darwin’s theory as an example of the general principle that the present arises from the materials and forms of the past.
Introduction
Charles Darwin’s Theory of Evolution represents a giant leap in human understanding. It explains and unifies all of biology – thousands of years of natural history from before Darwin’s time, as well as the 150 years of genetics, molecular biology, and even ecology since Darwin published the theory. It directs our responses to disease and our practice of agriculture. It enlightens conservation biology. It has the potential to guide our future decisions about biotechnology. Apart from science, the Theory of Evolution has dramatically changed how we think about ourselves and how we relate to the world. Because the theory has influenced so many aspects of human life, it is crucial that you understand it thoroughly.
The
“Theory of Evolution” contains two major ideas:
The first is evolution itself.
Present life has arisen gradually from past life forms. The millions of species of plants, animals, and microorganisms that live on Earth today are related by descent from common ancestors.
The second describes how evolution happens.
Natural selection explains how the diversity of life has arisen through time.
The main goal of this lesson will be to clarify these ideas. The lesson will begin by exploring Darwin’s experiences. The ideas of others who influenced Darwin’s thinking will also be presented. Finally, the content and significance of the theory itself will be analyzed.
The Voyage of the Beagle
Captained by a 26-year-old Royal Navyman and carrying a 22-year-old “gentleman’s companion” who collected beetles competitively, His Majesty’s Ship Beagle set sail on one of the shortest days of the year 1831 to chart South American coastal waters. Alarmed by the suicides of his own uncle and the previous Beagle commander, Captain Robert FitzRoy had sought a social and educational equal to accompany him at dinner and in scientific endeavors throughout the anticipated two-year voyage. Charles Darwin, financed by his wealthy father, assumed the unpaid positions of the ship’s naturalist and captain’s friend.
Figure 12.1
The HMS carried 22-year-old Charles Darwin as an unpaid naturalist and gentleman companion for the ships captain.
Darwin resisted his family’s hopes that he become a doctor or clergyman. During the two years before he dropped out of medical studies, he was repulsed by the brutality of surgery but fascinated by natural history – field observations of plants, animals, rocks, and fossils. He observed marine mammals on the English coast, and learned taxidermy from a freed slave whose talk of rain forests ignited curiosity in Darwin. After his disappointed father switched him to a school of theology, Darwin again gravitated toward natural history, becoming a protégée of botanist John Steven Henslow in order to learn the popular pastime of competitive beetle collecting. He managed to pass his theology exams, but his interests continued to reflect his passion for natural history, including William Paley’s “argument for divine design in nature.” He had just postponed entry into the clergy in order to study geology – mapping rock layers in Wales – when he received the invitation to join FitzRoy on the Beagle.
Planned to last two years, the voyage shown in Figures above and below, stretched to five years. Darwin spent over 3 years of this time on land, carefully observing rock formations and collecting animals, plants, and fossils (Figure below). Throughout the journey, he used his observations to develop a series of ideas which later became the foundation for his theory of evolution by natural selection (Figure below). A few of his ideas, observations, and experiences follow.
Figure 12.2
The s voyage continued for nearly five years, although original plans called for only two. Darwin spent over three years of that time on land, collecting plants, animals, and fossils, and developing his ideas about evolution and natural selection.
Rock and Fossil Formations
During the voyage of the Beagle, Darwin made a number of geological observations that helped form his theory. Rock and fossil formations that he observed suggested that continents and oceans had changed dramatically over time.
Darwin found rocks at a continental divide, 13,000 feet above sea level, which contained fossil seashells.
A river in Argentina rose gradually through a series of plateaus, which Darwin and FitzRoy interpreted as ancient beaches.
After experiencing a volcanic eruption and an earthquake in Chile, Darwin found a bed of newly dead mussels, which the quake had lifted nine feet above the sea.
A petrified forest embedded in sandstone at 7,000 feet had been a sunken coastal woodland, buried in sand and then uplifted into mountains.
Near Lima, Darwin recognized coral atolls as the result of sinking volcanoes, with coral adding layer after layer to keep the living reef close to the sunlit surface, as shown in Figure below.
Figure 12.3
Darwin explained coral atolls in terms of slowly sinking volcanoes. Evidence for slow geologic change contributed a great deal to his thinking about slow changes in life.
Tropical Rain Forests and Many New Plant, Animal, and Fossil Species
During the voyage of the Beagle, Darwin made a number of observations of plants, animals, and fossils that helped him form his theory. Observations of tropical rain forests and many new plant, animal, and fossil species encouraged Darwin to reconsider the source of the vast diversity of life.
In Brazil, Darwin collected great numbers of insects – especially beetles!
Inland from Montevideo, Darwin dug up the hippopotamus-like skull of an extinct giant capybara.
After collecting his first marsupial in Australia, Darwin exclaimed that some people might think “'Surely two distinct Creators must have been [at] work."
Figure 12.4
Marine Iguanas (left) and Blue-footed Boobies (right) were among the tremendous variety of new and very different plants and animals Darwin identified during the voyage of the . He developed his ideas about evolution and natural selection to explain the remarkable similarities and differences he had observed.
Native Cultures Raised Questions
During the voyage of the Beagle, observations of native cultures led Darwin to question the relationship between humans and animals and the development of civilizations.
Disgusted by the enslavement of blacks in Brazil, Darwin argued with FitzRoy so fiercely that the captain temporarily banished him from dining.
At the tip of South America, Darwin wrote “I could not have believed how wide was the difference between savage and civilized man: it is greater than between a wild and domesticated animal.”
Darwin described New Zealand Maoris as savage, in contrast to missionary-influenced Tahitians.
Jemmy Buttons, a South American native who had “been civilized” in England, chose to stay in South America rather than continue with the Beagle - to the great dismay of the Englishmen convinced of their civilization’s superiority.
Figure 12.5
Darwins encounters with native cultures influenced his thinking as much as his discoveries of fossils and new species. This painting was taken from original pictorial records of the voyage.
Sedimentary Rocks Implied Gradual Changes
Darwin also made a number of observations that implied gradual changes in both the Earth and in living organisms, as opposed to catastrophic changes, including:
Many inland sediments had clearly been deposited by quiet tides rather than catastrophic floods.
Gauchos, cowboys of Argentina, helped Darwin find and excavate fossils of gigantic extinct mammals, including armadillos and one of the largest mammals of all time, the ground sloth Megatherium (Figure below). Darwin recorded that these sediments bore no trace of a Biblical flood.
Figure 12.6
Darwin found two separate fossils of one of the largest mammals of all time, a giant ground sloth, . He noted that they were found in sediments which had been deposited slowly over long periods of time, rather than suddenly as by a catastrophic flood.
Life on Island Chains
The distribution of life on island chains challenged the dogma of the unchangability of species. The Galapagos Islands are arguably where Darwin made his most influential observations. The Galapagos Islands are a group of 16 volcanic islands near the equator about 600 miles from the west coast of South America. Darwin was able to spend months on foot exploring the islands.
Darwin noted that locals could distinguish each island’s variation of Galapagos tortoise, shown in Figure below. Surprisingly, he did not collect their shells, despite dining on the giant reptiles during the voyage.
A series of birds now known as the Galapagos (or Darwin’s) finches were also specific to certain islands. Darwin failed to label the locations in which he had collected these rather drab
-looking birds, but fortunately, FitzRoy and the ship’s surgeon were more careful with their collections.
Darwin interpreted the different Galapagos mockingbirds as varieties, but wrote that if varieties were a step on the way to new species, “such facts (would) undermine the stability of Species.”
Figure 12.7
Like many seamen, Darwin and the crew of the dined on Galapagos tortoise, a convenient animal to carry live on long voyages. However, locals living on the islands claimed the tortoises varied according to the islands from which they came, and this idea later played an important role in Darwins thinking about the origins of species.
Throughout the trip, Darwin shown in Figure below, sent his mentor, Henslow, collections of plants, animals, insects, and fossils – many of which were previously unknown. While Darwin traveled, Henslow promoted his work by sharing his geological writings and fossils with renowned naturalists. By the time the Beagle returned to England in October of 1836, Darwin himself had been accepted as an established naturalist. His father set up investment accounts to fund his son’s career as a “gentleman scientist.” At that time, governments and universities did not fund scientific research, so only independently wealthy individuals could afford to practice pure science. This position gave Darwin the contacts, resources, and freedom he needed to develop his ideas into the theory of evolution by natural selection.