Monday 8 May 2006
Tuesday 9 May 2006
Book Chapter 5 - Evolution
My Notes:
Section 1
Change over Time
• Evolution is the process in which inherited characteristics within a population change over generations, sometimes giving rise to new species. Scientists continue to develop theories to explain how evolution happens.
• Evidence that organisms evolve can be found by comparing living organisms to each other and to the fossil record. Such comparisons provide evidence of common ancestry.
• Scientists think that modern whales evolved from an ancient, land-dwelling mammal ancestor. Fossil organisms that support this hypothesis have been found.
• Evidence of common ancestry among living organisms is provided by comparing DNA and inherited traits. Species that have a common ancestor will have traits and DNA that are more similar to each other than to those of distantly related species.
Evolution of Whales and Other Mammals
• Scientists think that all mammals evolved from a shrew like ancestor. This ancestor survived the mass extinction that wiped out the dinosaurs about 65 million years ago. This hypothesis is supported by fossils formed during and after the time of the dinosaurs.
• The first ocean-dwelling mammals appeared in the fossil record about 50 million years ago. Scientists think that these mammals were the ancestors of whales and shared an ancestor with the artiodactyl group (even-toed, hoofed mammals). However, other types of aquatic mammals, such as dugongs, manatees, and sea lions, probably evolved separately and from later branches of the mammal lineage.
• In many ways, whales are more similar to their hoofed mammal relatives than they are to fish. Similarities include internal structures, behavior, and DNA. Also, whales swim by moving their tails up and down, in a motion similar to a gallop and to the swimming of an otter, whereas fish move their tails sideways.
Homologous Structures
• Homologous structures are anatomical features that have similar evolutionary and embryological origins and exhibit similar anatomical patterns. For example, bird wings, human arms, whale flippers, and deer forelimbs are all homologous. However, bird wings and butterfly wings are analogous structures because they function similarly but are anatomically dissimilar.
• Cellular components and biochemicals may also be homologous. For example, hemoglobin molecules from different vertebrate species have similar amino-acid sequences. But hemocyanin, which transports oxygen in crabs, has a very different sequence and is therefore analogous to hemoglobin; that is, the two molecules
The California halibut belongs to the family Bothidae, also known as the left-eyed flounders. Despite the name, about 40% of California halibut adults have both eyes on the right side of their body.
Convergent Evolution
When scientists study the fossils, skeletons, and DNA of species thought to be related, the scientists sometimes find that the organisms are not related at all. For example, the jerboa and the kangaroo rat look almost identical, but scientists have concluded that they have different ancestors. Such cases illustrate convergent evolution, where different species developed similar adaptations to similar environmental conditions and roles.
Frozen Fossils
In some cases, scientists can obtain DNA from ancient tissues that have not completely decomposed or fossilized. Two Japanese geneticists are hoping to create a mammoth-elephant hybrid by using tissue from a Siberian mammoth that died and was frozen thousands of years ago. However, the chances of finding intact DNA are small, and the genetic structures of mammoths and elephants are not fully compatible.
The human appendix is a vestigial organ, or an organ that performs little or no apparent function but that is thought to have had a function in ancestors. The appendix is a narrow tube attached to the large intestine. In chimpanzees, gorillas, and orangutans, the appendix is an intestinal sac that helps them digest tough plant material.
There are more than 100,000 living mollusk species, and at least 35,000 extinct forms are known from the fossil record. As a group, mollusks are very successful—there have been mollusks on Earth for nearly 600 million years.
The gastric brooding frogs of Australia, now extinct, incubated their tadpoles in their stomachs and gave birth to their young through their mouths!
Populations Versus Species
Understanding evolution requires understanding that changes in populations can lead to changes in species. Thus, it is important that students distinguish between populations and species. Reinforce these meanings with the following examples:
All domestic cats are the same species. Those that live in one city may be a population, but cats that live in different cities are probably not part of the same population. All of the same kind of lizard that live on an island are a population and may be the only population of a single species. All humans are the same species, with many populations. (Note however, that even professional biologists are sometimes unsure about the designation of closely related groups of organisms.)
Historic Paleontologist
Mary Anning (1799–1847) made some of the most important fossil discoveries of her time. She was born in Lyme Regis in southern Great Britain, an area with many fossils. Her father, a cabinetmaker and amateur fossil collector, died when Anning was 11 years old, leaving the family in debt. Anning’s fossil finding skills provided the family with needed income. Even before she reached her teens, Anning had discovered part of the first Ichthyosaurus to be recognized by scientists in London.
In the early 1820s, a professional fossil collector sold his private collection and gave the proceeds to the Anning family. He recognized that they had contributed many specimens for scientific investigation. Soon after, Mary Anning took charge of the family fossil business.
However, many of Anning’s finds ended up unaccredited. Many scientists could not accept that a person of her financial and educational background could have acquired such expertise. Have students research to find out one of Anning’s significant fossil finds (For example, she discovered the first plesiosaur).
How Many Toes?
Hoofed mammals, or ungulates, are classified into two major groups. The even-toed artiodactyls have either two or four toes on each foot. Examples are pigs, deer, and cows. The odd-toed perissodactyls carry their weight on a middle toe. Examples are horses, zebras, tapirs, and rhinoceroses.
Species Countdown
Present the following scenario to students:
Imagine that you are a scientific time traveler assigned to count the species in your home state 1,000 years from now. You know that, at present, your home state contains 2,300 animal species and 4,500 plant species. But many species are becoming endangered or extinct. Only 55% of the state’s species are expected to remain in existence after 1,000 years. How many specie should you expect to count during your visit to the future? (Tip: Round your answer to two significant figures.)
Adaptation on Purpose?
Students commonly confuse evolutionary adaptation with intentional change. For example, a student might say that an organism “learns” to adapt or “grows” an adaptation to a changing environment.
Explain to students that the evolution of adaptations is something that happens to populations over many generations. Evolution never happens within a single individual. Furthermore, new traits arise by chance and become adaptations in a population only if those traits are both advantageous to individuals and inherited by their offspring. Students may also confuse evolutionary adaptation with acclimation, such as adjustment to seasonal changes. Adaptations that enable organisms to adjust to changing conditions can evolve, but only if those abilities are passed on.
In 1938, some fishermen near the coast of South Africa caught an unusual fish called a coelacanth. Until that time, this type of fish was known only from fossils and was thought to have been extinct.
Baby blue whales can weigh about 9 tons (9,000 kg or 20,000 lb) at birth and can grow to 190 tons. Blue whales are baleen whales and are now the largest of all whales. The largest among the toothed whales is the sperm whale. The largest sperm whale on record weighed more than 50 tons. Toothed whales include orcas, dolphins, porpoises, narwhals, belugas, beaked whales, and bottle-nosed whales.
A Vestigial Tail
Scientists think that the tailbone in humans is a vestigial structure. In other words, it is an inherited remnant of the tails of humans’
In the late 1990s, analysis of genetic and hereditary molecular material from a variety of mammals showed that whales share more genetic similarities to hippopotamuses than to any other living mammal group.
Section 2
How Does Evolution Happen?
Darwin explained that evolution occurs through natural selection. His theory has four parts:
1. Each species produces more offspring than will survive to reproduce.
2. Individuals within a population have slightly different traits.
3. Individuals within a population compete with each other for limited resources.
4. Individuals that are better equipped to live in an environment are more likely to survive to reproduce.
Alfred Russel Wallace
Alfred Wallace (1823–1913) was born in England. He came from a poor family and had no formal scientific education. Though originally interested in botany, he began to study insects with the encouragement of British naturalist Henry Walter Bates, whom Wallace met when he was about 20 years old. Bates and Wallace explored the Amazon from 1848 to 1852 and found much evidence to support a theory of evolution by natural selection.
From 1854 to 1862, Wallace traveled in the Malay Archipelago to find more evidence of evolution. In 1855, he published a preliminary essay, “On the Law Which Has Regulated the Introduction of New Species.” Meanwhile, nearly 20 years after Charles Darwin’s voyage on the HMS Beagle, Darwin was still mulling over his data. In 1858, Wallace mailed an essay to Darwin that explained Wallace’s theory that natural selection pressures species to change.
In July 1858, Wallace’s essay was presented along with a paper by Darwin at a meeting of the Linnean Society in London. In the following year, after nearly two decades of delay (because of his doubts and repeated analysis), Darwin published On the Origin of Species by Means of Natural Selection.
Charles Lyell
Charles Lyell (1797–1875), the eldest of 10 children, was born in Scotland and raised in England. His father was a naturalist who traveled with him to collect butterflies and aquatic insects, informal research that Lyell continued throughout college. Lyell’s research in geology led him to the belief that natural processes occurring over millions of years have shaped the Earth’s features. This idea was known as uniformitarianism. Lyell’s work influenced Darwin’s formulation
The giant tortoises of the Galápagos Islands weigh up to 270 kg and can live for more than 150 years.
Form and Function
Present and identify to students the following pieces of clothing: sneaker, dress pump, loafer, necktie, scarf, anklet, knee sock, baseball cap, and ski cap. Discuss the ways that all these items are related and how some are more closely related than others. (Related items are best suited for one particular function.) Explain that this relationship of similarities and differences is what scientists such as Charles Darwin observe in studying organisms.
While displaying a world map or atlas, explain the following: The Galápagos Islands are officially part of the country of Ecuador, though they are 1,000 km west of the mainland. They are a group of 19 volcanically formed islands. Though they have a land area of only 8,000 km2, they are dispersed over almost 60,000 km2 of the Pacific Ocean. Biologists now know that unique new species are likely to arise under these conditions.
Bird Barrier
Locate the Rocky Mountains on a map. Explain to students that bird identification guides for North America usually classify birds into those that are east of the Rocky Mountains and those that are west of the Rocky Mountains. Brainstorm reasons why ornithologists might use this system. (Sample answer: because the Rockies present a large geographical barrier.)
As a result of selective breeding, the smallest horse is the Falabella, which is only about 76 cm tall. The largest is the Shire, originally bred in England. It can grow more than 1.73 m high at the shoulder and weigh as much as 910 kg.
The full title of Thomas Malthus’s famous essay was “An Essay on the Principle of Population, as it Affects the Future Improvement of Society with Remarks on the Speculations of Mr. Godwin, M. Condorcet, and Other Writers.” Malthus’s work was important in influencing ecological scientists and prompting social planners to consider the potential problems of rapid population growth. However, Malthus was wrong in his projections of the growth of food supplies. The use of machinery, fossil fuels, and chemicals since Malthus’s time enabled food production to increase more rapidly than
Two Kinds of Growth
h Have students examine Figure 6. Ask students to describe the behavior of the graph for food supply. (It rises steadily in a straight line.) Explain that the line graphing food supply represents linear growth and increases by adding a certain amount in each time interval. Next, ask students to describe the behavior of the graph for human population. (It rises quickly and in a curved line.) Explain that the line graphing human population represents exponential growth and increases by multiplying by a certain percentage in each time interval.
In 1809, French naturalist Jean Baptiste Lamarck’s theory of evolution by acquired characteristics stated that if an animal changed a body part through muse or non-use, that change would be inherited by its offspring. For example, larger leg muscles as a result of extensive running would be passed on to the next generation. However, genetic studies in the 1930s and 1940s disproved
Section 3
Natural Selection in Action
Natural selection explains how populations adapt to changes in their environment. A variety of examples of such adaptations can be found.
Natural selection also explains how one species may evolve into another. Speciation occurs as populations undergo separation,
Adaptive Coloration
Penguins, puffins, killer whales, and blue sharks are just some of the ocean animals that have white bellies and black or dark blue dorsal surfaces. This type of coloration is called counter-
shading. When seen from below, the white underside helps the animal blend into the lighter sky above the water. When viewed from above, the dark coloration makes the animal difficult to see against the ocean depths.
Sexual Selection
Sexual selection is the term for the selection of traits brought about by a specific pattern of mating. In many sexual organisms, members of one sex must compete with each other for access to mates. Biologists think this behavior results when one sex’s investment in the next generation is greater than that of the other sex. At an extreme, the “choosiness” of one sex may drive the evolution of traits that confer no other apparent advantage to the opposite sex. The long tails and colorful plumage of many male birds are considered examples of such “runaway sexual selection.”
Tuskless Elephants
It is important understand that there were always tuskless elephants in the wild populations. These animals were naturally tuskless—they were born without and never developed tusks. Because tuskless elephants are not hunted, are more likely to pass their traits future generations.
Natural Pest Control
The use of natural predators against insect pests can provide an alternative to chemical insecticides.
Ladybugs, for example, which are actually beetles, are used to combat infestations of aphids, whiteflies, fruitworms, mites, broccoli worms, and tomato hornworms. Ladybugs can be purchased in large numbers and released on crops. Many species of bats are voracious hunters of mosquitoes and other small insects. Bat houses are becoming increasingly popular. Encourage students to research methods for encouraging ladybugs, bats, and other insect predators.
In several species, typical courtship behaviors involve one sex offering food to the other sex. For example, males of the fairy tern fly around the female and offer her a mackerel. In many spider species, males offer an insect carcass to the female. In some spider species, such as the Australian redback spider, the male himself may become a meal!
Some species that have adapted to live in total darkness no longer even have eyes! Just as whales have evolved into legless forms, these species have completely adapted to life without light, and some have evolved forms lacking eyes altogether. There are blind cave fish, eels, salamanders, worms, shrimp,
Some species that have adapted to live in total darkness no longer even have eyes! Just as whales have evolved into legless forms, these species have completely adapted to life without light, and some have evolved forms lacking eyes altogether. There are blind cave fish, eels, salamanders, worms, shrimp, crayfish, spiders, beetles, and crickets.
NSTA SciLinks
NSTA SciLinks is maintained by the National Science Teachers Association to provide you with interesting, up-to-date links that will enrich the chapter.
Topic: Species and Adaptation SciLinks code: HSM1433
Topic: Fossil Record SciLinks code: HSM0615
Topic: Galápagos Islands SciLinks code: HSM0631
Topic: Darwin and Natural Selection SciLinks code: HSM0378
