Limitations of this evaluation and lessons for future evaluations

Improvements in microscopes during the 1800s permitted cytol-ogists to study the production of gametes by direct observa-tion of reproductive tissues. Interpreting the observaobserva-tions was

Figure 1.18

An early nineteenth-century micrographic drawing of sperm from (1) guinea pig, (2) white mouse, (3) hedgehog, (4) horse, (5) cat, (6) ram, and (7) dog. Some biologists initially interpreted these as parasitic worms in the semen, but in 1824, Jean Prévost and Jean Dumas correctly identifi ed their role in egg fertilization.

1 5 4 3

6

7 2

initially diffi cult, however. Some prominent biologists hypoth-esized, for example, that sperm were parasitic worms in semen ( Figure 1.18 ). This hypothesis was soon falsifi ed, and the true nature of gametes was clarifi ed. As the precursors of gametes prepare to divide early in gamete production, the nuclear mate-rial condenses to reveal discrete, elongate structures called chro-mosomes. Chromosomes occur in pairs that are usually similar but not identical in appearance and informational content. The number of chromosomal pairs varies among species. One mem-ber of each pair is derived from the female parent and the other from the male parent. Paired chromosomes are physically associ-ated and then segregassoci-ated into different daughter cells during cell division prior to gamete formation ( Figure 1.19 ). Each resulting gamete receives one chromosome from each pair. Different pairs of chromosomes are sorted into gametes independently of each other. Because the behavior of chromosomal material during gamete formation parallels that postulated for Mendel’s genes, Sutton and Boveri in 1903 through 1904 hypothesized that chro-mosomes were the physical bearers of genetic material. This hypothesis met with extreme skepticism when fi rst proposed. A long series of tests designed to falsify it nonetheless showed that its predictions were upheld. The chromosomal theory of inheri-tance is now well established.

Figure 1.19

Paired chromosomes being separated before nuclear division in the process of forming gametes.

S U M M A R Y

Zoology is the scientifi c study of animals, and it is part of biol-ogy, the scientifi c study of life. Animals and life in general can be identifi ed by attributes that they have acquired over their long evo-lutionary histories. The most outstanding attributes of life include

chemical uniqueness, complexity and hierarchical organization, reproduction, possession of a genetic program, metabolism, devel-opment, interaction with the environment, and movement. Biologi-cal systems comprise a hierarchy of integrative levels (molecular,

hic70049_ch01_001-020.indd 19

hic70049_ch01_001-020.indd 19 7/12/07 2:13:53 PM7/12/07 2:13:53 PM

cellular, organismal, populational, and species levels), each of which demonstrates a number of specifi c emergent properties.

Science is characterized by the acquisition of knowledge by constructing and then testing hypotheses through observations of the natural world. Science is guided by natural law, and its hypoth-eses are testable, tentative, and falsifi able. Zoological sciences can be subdivided into two categories, experimental sciences and evolu-tionary sciences. Experimental sciences use the experimental method to ask how animals perform their basic metabolic, developmental, behavioral, and reproductive functions, including investigations of their molecular, cellular, and populational systems. Evolutionary sciences use the comparative method to reconstruct the history of life, and then use that history to understand how diverse species and their molecular, cellular, organismal, and populational prop-erties arose through evolutionary time. Hypotheses that withstand

repeated testing and therefore explain many diverse phenomena gain the status of a theory. Powerful theories that guide extensive research are called “paradigms.” The major paradigms that guide the study of zoology are Darwin’s theory of evolution and the chromo-somal theory of inheritance.

The principles given in this chapter illustrate the unity of bio-logical science. All components of biobio-logical systems are guided by natural laws and are constrained by those laws. Living organisms arise only from other living organisms, just as new cells can be pro-duced only from preexisting cells. Reproductive processes occur at all levels of the biological hierarchy and demonstrate both heredity and variation. Interaction of heredity and variation at all levels of the biological hierarchy produces evolutionary change and has gener-ated the great diversity of animal life documented throughout this book.

R E V I E W Q U E S T I O N S

Why is life diffi cult to defi ne?

What are the basic chemical differences that distinguish living from nonliving systems?

Describe the hierarchical organization of life. How does this organization lead to the emergence of new properties at different levels of biological complexity?

What is the relationship between heredity and variation in reproducing biological systems?

Describe how evolution of complex organisms is compatible with the second law of thermodynamics.

What are the essential characteristics of science? Describe how evolutionary studies fi t these characteristics whereas “scientifi c creationism” or “intelligent-design theory” does not.

Use studies of natural selection in British moth populations to illustrate the hypothetico-deductive method of science.

1.

2.

3.

4.

5.

6.

7.

How do we distinguish the terms hypothesis, theory, paradigm, and scientifi c fact?

How do biologists distinguish experimental and evolutionary sciences?

What are Darwin’s fi ve theories of evolution (as identifi ed by Ernst Mayr)? Which are accepted as fact and which continue to stir controversy among biologists?

What major obstacle confronted Darwin’s theory of natural selection when it was fi rst proposed? How was this obstacle overcome?

How does neo-Darwinism differ from Darwinism?

Describe the respective contributions of the genetic approach and cell biology to formulating the chromosomal theory of inheritance.

8.

9.

10.

11.

12.

13.

S E L E C T E D R E F E R E N C E S

Futuyma, D. J. 1995. Science on trial: the case for evolution. Sunderland, Massachusetts, Sinauer Associates, Inc. A defense of evolutionary biology as the exclusive scientifi c approach to the study of life’s diversity.

Kitcher, P. 1982. Abusing science: the case against creationism. Cambridge, Massachusetts, MIT Press. A treatise on how knowledge is gained in science and why creationism does not qualify as science. Note that the position refuted as “scientifi c creationism” in this book is equivalent in content to the position more recently termed “intelligent-design theory.”

Kuhn, T. S. 1970. The structure of scientifi c revolutions, ed. 2, enlarged.

Chicago, University of Chicago Press. An infl uential and controversial commentary on the process of science.

Mayr, E. 1982. The growth of biological thought: diversity, evolution and inheritance. Cambridge, Massachusetts, The Belknap Press of Harvard University Press. An interpretive history of biology with special reference to genetics and evolution.

Medawar, P. B. 1989. Induction and intuition in scientifi c thought. London, Methuen & Company. A commentary on the basic philosophy and methodology of science.

Moore, J. A. 1993. Science as a way of knowing: the foundations of modern biology. Cambridge, Massachusetts, Harvard University Press. A lively, wide-ranging account of the history of biological thought and the workings of life.

Perutz, M. F. 1989. Is science necessary? Essays on science and scientists.

New York, E. P. Dutton. A general discussion of the utility of science.

Pigliucci, M. 2002. Denying evolution: creationism, scientism, and the nature of science. Sunderland, Massachusetts, Sinauer Associates, Inc.

A critique of science education and the public perception of science.

Rennie, J. 2002. 15 answers to creationist nonsense. Sci. Am. 287:78–85 (July). A guide to the most common arguments used by creationists against evolutionary biology, with concise explanations of the scientifi c fl aws of creationists’ claims.

O N L I N E L E A R N I N G C E N T E R

Visit www.mhhe.com/hickmanipz14e for chapter quizzing, key term fl ash cards, web links, and more!

hic70049_ch01_001-020.indd 20

hic70049_ch01_001-020.indd 20 7/12/07 2:13:54 PM7/12/07 2:13:54 PM

C H A P T E R

2

The Origin and Chemistry of Life

Spontaneous Generation of Life?

From ancient times, people commonly thought that life arose repeat-edly by spontaneous generation from nonliving material in addition to parental reproduction. For example, frogs appeared to arise from damp earth, mice from putrefi ed matter, insects from dew, and mag-gots from decaying meat. Warmth, moisture, sunlight, and even star-light often were mentioned as factors that encouraged spontaneous generation of living organisms.

Among the efforts to synthesize organisms in the laboratory is a recipe for making mice, given by the Belgian plant nutritionist Jean Baptiste van Helmont (1648). “If you press a piece of under-wear soiled with sweat together with some wheat in an open jar, after about 21 days the odor changes and the ferment . . . changes the wheat into mice. But what is more remarkable is that the mice which came out of the wheat and underwear were not small mice, not even miniature adults or aborted mice, but adult mice emerge!”

In 1861, the great French scientist Louis Pasteur convinced scientists that living organisms cannot arise spontaneously from nonliving matter. In his famous experiments, Pasteur introduced fermentable material into a fl ask with a long S-shaped neck that

was open to air. The fl ask and its contents were then boiled for a long time to kill any microorganisms that might be present. After-ward the fl ask was cooled and left undisturbed. No fermentation occurred because all organisms that entered the open end were deposited in the neck and did not reach the fermentable material.

When the neck of the fl ask was removed, microorganisms in the air promptly entered the fermentable material and proliferated. Pasteur concluded that life could not originate in the absence of previously existing organisms and their reproductive elements, such as eggs and spores. Announcing his results to the French Academy, Pasteur proclaimed, “Never will the doctrine of spontaneous generation arise from this mortal blow.”

All living organisms share a common ancestor, most likely a population of colonial microorganisms that lived almost 4 billion years ago. This common ancestor was itself the product of a long period of prebiotic assembly of nonliving matter, including organic molecules and water, to form self-replicating units. All living organ-isms retain a fundamental chemical composition inherited from their ancient common ancestor.

Earth’s abundant supply of water was critical for the origin of life.

hic70049_ch02_021-036.indd 21

hic70049_ch02_021-036.indd 21 7/9/07 3:55:20 PM7/9/07 3:55:20 PM

A

ccording to the big-bang model, the universe originated from a primeval fi reball and has been expanding and cooling since its inception 10 to 20 billion years ago.

The sun and planets formed approximately 4.6 billion years ago from a spherical cloud of cosmic dust and gases. The cloud col-lapsed under the infl uence of its own gravity into a rotating disc.

As material in the central part of the disc condensed to form the sun, gravitational energy was released as radiation. The pressure of this outwardly directed radiation prevented a collapse of the nebula into the sun. The material left behind cooled and eventu-ally produced the planets, including earth ( Figure 2.1 ).

In the 1920s, Russian biochemist Alexander I. Oparin and British biologist J. B. S. Haldane independently proposed that life originated on earth after an inconceivably long period of

“abiogenic molecular evolution.” Rather than arguing that the first living organisms miraculously originated all at once, a notion that formerly discouraged scientifi c inquiry, Oparin and Haldane argued that the simplest form of life arose gradually by the progressive assembly of small molecules into more complex organic molecules. Molecules capable of self-replication eventu-ally would be produced, ultimately leading to assembly of living microorganisms.

In document Evaluation of signs of safety in 10 pilots, July 2017 (Page 99-102)