The Ecology Book
Page 2
The future
Modern ecology has come a long way since the science was first recognized. It now draws on many disciplines. In addition to zoology, botany, and their microdisciplines, it relies on geology, geomorphology, climatology, chemistry, physics, genetics, sociology, and more. Ecology influences local and national government decisions about urbanization, transportation, industry, and economic growth. The challenges posed by climate change, rising sea levels, habitat destruction, the extinction of species, plastic and other forms of pollution, and a looming water crisis pose serious threats to human civilization. They demand radical policy responses based on sound science. Ecology will provide the answers. It is up to governments to apply them.
“Even in the vast and mysterious reaches of the sea we are brought back to the fundamental truth that nothing lives to itself.”
Rachel Carson
INTRODUCTION
Ancient myths, religions, and philosophies all reflect an enduring fascination with how the world began and man’s place in the story of life on Earth. In the West, Christianity held that all animals and plants were the result of a perfect creation. On the chain or ladder of being, no species could ever move from one position to another. Species were immutable, an idea called essentialism.
The 18th-century Age of Enlightenment began to challenge orthodox Christian beliefs. French zoologist Jean-Baptiste Lamarck rejected the prevailing Bible-based notion of Earth being only a few thousand years old. He argued that organisms must have changed from simple life forms to more complex ones over millions of years, and that the “transmutation” of species was the driving force behind this change. He speculated that characteristics acquired by animals during their lifetime were inherited by the next generation: giraffes, for example, became slightly longer-necked by stretching up to reach higher leaves, and passed this trait to their offspring; over many generations, giraffes grew longer and longer necks.
Fossil evidence of extinct life forms with features that resembled modern descendants, found by pioneering geologists such as Georges Cuvier, also suggested Earth had more ancient origins. Meanwhile James Hutton and Charles Lyell argued that geological features could be accounted for by the constant, ongoing processes of erosion, and deposition—a view called uniformitarianism. Because these processes take place slowly, Earth’s history had to be much longer than was previously thought.
Natural selection
In 1858, Charles Darwin and Alfred Russel Wallace delivered a paper that would change biology forever. Darwin’s observations on the epic voyage of the Beagle (1831–36), his correspondence with other naturalists, and the influence of Thomas Malthus’s writings inspired Darwin’s insight that evolution came about by what he called natural selection. He spent 20 years gathering supporting data, but when Wallace wrote to him with the same idea, Darwin realized it was time to go public. His subsequent book, On the Origin of Species by Means of Natural Selection, provoked outrage.
Although the idea of evolution became widely accepted, the mechanism that made natural selection possible was not yet known. In 1866, an Austrian monk called Gregor Mendel made a huge contribution to genetics when he published his findings on heredity in pea plants. Mendel described how dominant and recessive traits pass from one generation to the next, by means of invisible “factors” that we now call genes.
The rediscovery of Mendel’s work in 1900 initially sparked sharp debate between his supporters and many Darwinians. At the time, evolution was believed to be based on the selection of small, blending variations, but Mendel’s variations clearly did not blend. Three decades later, geneticist Ronald Fisher and others argued that the two schools of thought were complementary, rather than contradictory. In 1942, Julian Huxley articulated the synthesis between Mendel’s genetics and Darwin’s theory of natural selection in his book Evolution: The Modern Synthesis.
The double helix
Advances in technology such as X-ray crystallography led to more discoveries in the 1940s and ’50s, and the foundation of the new discipline of molecular biology. In 1944, chemist Oswald Avery identified deoxyribonucleic acid (DNA) as the agent for heredity. Rosalind Franklin and Raymond Gosling photographed strands of the DNA molecule in 1952, and James Watson and Francis Crick confirmed its double helix structure the following year. Crick then showed that genetic information is “written” on DNA molecules. The errors that occur when DNA copies itself create mutations—the raw materials for evolution. By the 1980s it was possible to map and manipulate the genes of individuals and species. In the 1990s, the mapping the human genome paved the way for medical research into gene therapy.
Ecologists also want to establish whether genes influence behavior. Back in 1964, William D. Hamilton popularized the concept of genetic relatedness (“kin selection”) to explain altruistic behavior in animals. In The Selfish Gene (1976), Richard Dawkins further advanced the gene-centered approach. It is clear that aspects of evolutionary biology will still spark debate as long as ecologists continue to develop Darwin’s theory.
IN CONTEXT
KEY FIGURES
The Comte de Buffon (1707–88), Jean-Baptiste Lamarck (1744–1829)
BEFORE
1735 Swedish botanist Carl Linnaeus publishes Systema Naturae, a system of biological classification that later helped to determine species’ ancestry.
1751 In “Système de la nature” French philosopher Pierre Louis Moreau de Maupertuis introduces the idea that features can be inherited.
AFTER
1831 Etienne Geoffroy Saint-Hilaire writes that sudden environmental change can cause a new species to develop from an existing organism.
1844 In Vestiges of the Natural History of Creation, Scottish geologist Robert Chambers argues—anonymously—that simple creatures have evolved into more complex species.
Before the 18th century, most people believed that plant and animal species stayed unchanged throughout time—a view now known as essentialism. This idea came under challenge as a result of two developments: the intellectual movement known as the Enlightenment (c. 1715–1800), and the Industrial Revolution (1760–1840).
The Enlightenment was marked by scientific progress and increased questioning of religious orthodoxy, such as the claim that God created Earth and all living things in seven days. Then, as the Industrial Revolution gathered pace, canals, railroads, mines, and quarries cut through rock strata and revealed thousands of fossils, mostly of animal and plant species that no longer existed and had never been seen before. These suggested that life began long before the widely accepted creation date of 4400 BCE, deduced from biblical sources.
Animal adaptation
In the late 1700s, French scientist Georges-Louis Leclerc, Comte de Buffon, upset church authorities by asserting that Earth was much older than the Bible suggested. He believed it was formed from molten material, struck off the Sun by a comet, that had taken 70,000 years to cool (a huge underestimate, in fact). As Earth cooled, species had appeared, died off, and were finally replaced by ancestors of those known today. Noting similarities among animals such as lions, tigers, and cats, Buffon deduced that 200 species of quadrupeds had evolved from just 38 ancestors. He also believed that changes in body shape and size in related species had occurred in response to living in different environments.
In 1800, French naturalist Jean-Baptiste Lamarck went further. In a lecture at the Museum of Natural History in Paris, he argued that traits acquired by a creature during its lifetime could be inherited by its offspring—and that a buildup of such changes over many generations could radically alter an animal’s anatomy.
Lamarck wrote several books in which he developed this idea of transmutation. He argued, for instance, that the use or nonuse of body parts eventually resulted in such features becoming stronger, weaker, bigger, or smaller in a species. For example, the ancestors of moles probably had good eyesight, but over generations this deteriorated because moles did not require vision as they burrowed underground. Similarly, giraffes g
radually developed longer necks to enable them to reach leaves growing high up in trees.
“Nature is the system of laws established by the Creator for the existence of things and for the succession of creatures.”
The Comte de Buffon
Drivers of evolution
Larmarck’s ideas about inherited acquired traits were part of a wider early theory of evolution. He also believed that the earliest, simplest forms of life had emerged directly from nonliving matter. Lamarck identified two main “life forces” driving evolutionary change. One, he believed, made organisms develop from simple to more complex forms in a “ladder” of progress. The other, via the inheritance of acquired traits, helped them adapt better to their environment. When Charles Darwin developed his theory of evolution by means of natural selection, he would reject many of Lamarck’s ideas, but both men shared the belief that complex life evolved over an immense period of time.
Fossil finds changed ideas about how life began. The first example of an articulated plesiosaur—Plesiosaurus dolichodeirus—was discovered in 1823 by Mary Anning in Dorset, England.
“… continuous use of any organ gradually strengthens, develops and enlarges that organ.”
Jean-Baptiste Lamarck
JEAN-BAPTISTE LAMARCK
Born in 1744, Jean-Baptiste Lamarck attended a Jesuit college before joining the French army. Forced by an injury to resign, he studied medicine and then pursued his passion for plants, working at the Jardin du Roi (Royal Garden) in Paris. Supported by the Comte de Buffon, Lamarck was elected to the Academy of Sciences in 1779. When the Jardin’s main building became the new National Museum of Natural History during the French Revolution (1789–99), Lamarck was placed in charge of the study of insects, worms, and microscopic organisms. He coined the biological term “invertebrate” and often used the relatively simpler forms of such species to illustrate his “ladder” of evolutionary progress. However, Lamarck’s work was controversial and he died in poverty in 1829.
Key works
1802 Research on the Organization of Living Bodies
1809 Zoological Philosophy
1815–22 Natural History of Invertebrate Animals
See also: Extinction and change • Uniformitarianism • Evolution by natural selection • The rules of heredity
IN CONTEXT
KEY FIGURE
Georges Cuvier (1769–1832)
BEFORE
Late 1400s Leonardo da Vinci argues that fossils are the remains of living creatures, not just shapes spontaneously formed in the earth.
1660s English scientist Robert Hooke suggests that fossils are extinct creatures, since no similar forms can be found on Earth today.
AFTER
1841 English anatomist Richard Owen calls huge reptile fossils “dinosaurs.”
1859 Charles Darwin’s On the Origin of Species explains how evolution can occur through “natural selection.”
1980 US scientists Luis and Walter Alvarez present evidence that an asteroid hit Earth at the time of the extinction of the dinosaurs.
In the early days of studying fossils, many people denied they could be extinct species. They failed to see why God would create and destroy creatures before humans ever appeared, arguing that unfamiliar fossil species might still be living somewhere on Earth. In the late 18th century, French zoologist Georges Cuvier looked into this by exploring the anatomy of living and fossil elephants. He proved that fossil forms such as mammoths and mastodons were anatomically distinct from living elephants, so they must represent extinct species. (It was highly unlikely that they still lived on Earth without being noticed.)
Cuvier believed that Earth had experienced a series of distinct ages, each of which ended with a “revolution” that destroyed existing flora and fauna. He did not, though, believe that the evidence of fossil remains supported a theory of evolution. Nevertheless, Cuvier’s central views have continued to win support, and modern evidence points to at least five catastrophic mass extinction events in Earth’s past, including the one that wiped out the dinosaurs. Unlike Cuvier, however, today’s scientists know that life is not recreated out of nothing after a catastrophe. Rather, when a mass extinction event kills off many species, those left will evolve and multiply—sometimes relatively quickly—to fill vacant ecological niches, as the mammals did after the age of the dinosaurs.
Cuvier coined the name “mastodon” for its Greek meaning of “breast tooth,” referring to the nipplelike patterns on the creature’s teeth, which were unlike those of any living elephants.
See also: Evolution by natural selection • Ecological niches • An ancient ice age • Mass extinctions
IN CONTEXT
KEY FIGURE
James Hutton (1726–97)
BEFORE
1778 The Comte de Buffon, a French naturalist, suggests that Earth is at least 75,000 years old—far older than most people believed at the time.
1787 German geologist Abraham Werner proposes that Earth’s layers of rock formed from a great ocean that once covered the entire planet. His followers became known as Neptunists.
AFTER
1802 James Hutton’s theory of uniformitarianism reaches a wider audience when Scottish geologist John Playfair publishes Illustrations of the Huttonian Theory of the Earth.
1830–33 Principles of Geology, by Scottish geologist Charles Lyell, supports and builds on the uniformitarian ideas of James Hutton.
Uniformitarianism is the theory that geological processes, such as the laying down of sediment, erosion, and volcanic activity, occur at the same rate now as they did in the past. The idea emerged in the late 18th century, as mining, quarrying, and increased travel brought ever more geological features to light, including unusual rock strata and previously unknown fossils, whose origins were then widely debated.
The generally accepted view that Earth was only a few thousand years old had been challenged by the Comte de Buffon, and in 1785 Scottish geologist James Hutton also argued for Earth’s far greater antiquity. Hutton’s ideas were formed during expeditions around Scotland to examine layers of rock. He believed that Earth’s crust was constantly changing, albeit mostly slowly, and could see no reason to suggest that the complex geological actions of layering, erosion, and uplifting took place faster in the distant past than they did in the present. Hutton also understood that most geological processes happen so gradually that the features he was discovering must be astronomically old.
Uniformitarianism was not generally accepted at once, not least because it challenged a literal interpretation of the creation stories of the Old Testament. However, a new generation of geologists, such as John Playfair and Charles Lyell, threw their intellectual weight behind Hutton’s ideas, which also inspired a young Charles Darwin.
“… from what has actually been, we have data for concluding [what] is to happen thereafter.”
James Hutton
See also: Early theories of evolution • Evolution by natural selection • Moving continents and evolution • Mass extinctions
IN CONTEXT
KEY FIGURE
Charles Darwin (1809–82)
BEFORE
1788 In France, Georges-Louis Leclerc, Comte de Buffon, completes his 36-volume Histoire Naturelle, outlining early ideas about evolution.
1809 Jean-Baptiste Lamarck proposes that creatures evolve by inheriting acquired traits.
AFTER
1869 Friedrich Miescher, a Swiss doctor, discovers DNA, although its genetic role is not yet understood.
1900 The laws of inheritance based on the pea plant experiments of Austrian scientist Gregor Mendel in the mid-1800s are rediscovered.
1942 British biologist Julian Huxley coins the term “modern synthesis” for the mechanisms thought to produce evolution.
Natural selection, a concept developed by British naturalist Charles Darwin and set out in his book On the Origin of Species by Means of Natural Selection (1859), is the key mechanism of evolution in organisms, resulting in d
ifferent survival rates and reproductive abilities. Those organisms that have higher breeding success pass on their genes to more of the next generation, so individuals with these characteristics become more common.
“Natural selection is daily and hourly scrutinizing, throughout the world, the slightest variations.”
Charles Darwin
To the Galapagos
The young Charles Darwin first began to consider evolution during his pioneering scientific expedition around the world aboard HMS Beagle from 1831 to 1836. As a young man, Darwin accepted the orthodox interpretation of the Bible, that Earth was only a few thousand years old. However, while he was on board the Beagle, Darwin read Scottish geologist Charles Lyell’s recently published Principles of Geology, in which Lyell demonstrated that rocks bore traces of tiny, gradual, and cumulative change over vast time periods—millions, rather than thousands of years. As Darwin looked at landscapes around the world that had been affected by processes of erosion, deposition, and volcanism, he began to speculate about animal species changing over very long time periods, and the reasons for such changes. By examining fossils and observing living animals, Darwin identified patterns; he noticed, for example, that extinct species had often been replaced by similar, but distinct, modern ones.