Chapter Two: Evolution: Constructing a Fundamental Scientific Theory

evolutionary synthesis

A unified theory of evolution that combines genetics with natural selection.

Mendel's Peas

A 1876 catalog illustration of Mendel's seed suppliers, showed some of the seven characteristics Mendel studied, each of which had two variants. For example: flower position, could be axial or terminal, while flower color could be white or purple.

mutation

A random change in a gene or chromosomes, creating a new trait that may be advantageous, deleterious, or neutral in effects on the organism.

population genetics

A specialty within the field of genetics; it focuses on the changes in gene frequencies and the effects of those changes on adaption and evolution.

gene flow

Admixture, or the exchange of alleles between two population

recessive

An allele that is expressed in an organism's phenotype if two copies are present, but is masked if the dominant allele is present.

adaptations

Changes in physical structure, function, or behavior that allow an organism or species to survive and reproduce in a given environment.

Darwin's Voyage

Charles Darwin ca. 1885, about 25 years after he set out on HMS Beagle. In this illustration, the ship is passing through the Strait of Magellan, during the South American stretch of its worldwide journey, whose ports of call are here mapped.

Lamarckism

First proposed by Lamarck, the theory of evolution through the inheritance of acquired characteristics in which an organism can pass on features acquired during its lifetime.

five scientific disciplines used by Darwin

Geology, paleontology, taxonomy, and systemics, demography and what is now called evolutionary biology.

HOW DID THE THEORY OF EVOLUTION COME TO BE?

In developing his theory of evolution by means of natural selection, Darwin drew geology, paleontology, taxonomy, and systemics, demography, and what is now called evolutionary biology. Scientists working on these disciplines had shown that: -earth is quite old and has changed considerably over its history, -fossils represent the remains of once-living, often extinct organisms and thus provide a record of the history of life on the planet, -life evolves over time, -groups of related species provide insight into evolutionary history, -the number of adults in the population tends to remain the same over time.

Georges Cuvier

One of Cuvier's most important contributions to science was the concept of extinction. Here, Cuvier is depicted examining a fish fossil. In his 1796 paper on fossil and living elephants, Cuvier suggested that mammoth remains-such as those shown here, from one of his many publications-represented a species different from any living elephant species and therefore, mammoth remains were from a species that had gone extinct. This idea was revolutionary, because the common perception was that God had created all species, none of which had ever gone extinct.

allele

One or more alternative forms of a gene.

fossils

Physical remains of part of all of once-living organisms, mostly bones and teeth, that have become materialized by the replacement of organic with inorganic materials.

dominant

Refers to an allele that is expressed in an organism's phenotype and that simultaneously masks the effects of another allele, if another one is present.

gene

The basic unit of inheritance; a sequence of DNA on a chromosome, coded to produce a specific protein.

adaptive radiation

The diversification of an ancestral group of organisms into new forms that are adapted to specific environmental niches.

catastrophism

The doctrine asserting that cataclysmic events (such as volcanoes, earthquakes, and floods), rather than evolutionary processes, are responsible for geologic changes throughout Earth's history.

genotype

The genetic makeup of an organism; the combination of alleles for a given gene.

phenotype

The physical expression of the genotype; it may be influenced by the environment.

natural selection

The process by which some organisms, with features that enable them to adapt to the environment, preferentially survive and reproduce, thereby increasing the frequency of those features in the population.

genetic drift

The random change in allele frequency from one generation to the next, with greater effect in small populations.

habitat

The specific area of the natural environment in which an organism lives.

chromosomes

The strand of DNA found in the nucleus of eukaryotes that contains hundreds or thousands of genes.

Geologic Strata

The succession of strata from oldest at the bottom to youngest at the top (as here, in Utah's Bryce Canyon) marks the formation of new land surfaces over time.

genus

A group of related species.

Lamarckism giraffes

According to the classic (through incorrect) example of Lamarckism, giraffes stretched to reach food at the tops of trees, their necks grew as a result, and they passed on these long necks to their offspring.

Mendel's seven studied pea characteristics

1. Flower Position (Axial or Terminal) 2. Flower Color (White or Purple) 3. Plant Height (Tall or Short) 4. Pea Shape (Round or Wrinkled) 5. Pea Color (Yellow or Green) 6. Pod Shape (Inflated or Constricted) 7. Pod Color (Yellow or Green)

deoxyribonucleic acid (DNA)

A double-stranded molecule that provides the genetic code for an organism, consisting of phosphate, deoxyribose sugar, and four types of nitrogen bases.

species

A group of related organisms that can interbreed and produce fertile, viable offspring.

Alfred Russel Wallace

Although Darwin often gets sole credit for the development of the theory of evolution through natural selection, Wallace (depicted ca. 1860) contributed substantially to evolutionary theory. Wallace was the leading authority on the geographic distribution of animals, for example, and was the first to recognize the concept of warning coloration in animals. In addition, he raised the issue of human impact on the environment a full century before it became a concern for the general public.

blending inheritance

An outdated, dis-reputed theory that the phenotype of an offspring was a uniform blend of the parents' phenotypes.

gemmules

As proposed by Darwin, the units of inheritance, supposedly accumulated in the gametes so they could be passed on to offspring.

Darwin Finches

Darwin studied the physical variation in finches living on different islands of the Galápagos. Among other attributes, he studied beak shape, which varied from island to island. Eventually, Darwin related each beak shape to diet, especially to the texture of food and how the food was acquired. Finches with larger beaks typically consumed harder foods, such as seeds and nuts, while finches with smaller beaks ate softer foods, such as berries. Darwin concluded that each finch species had adapted to the particular environment and food resources of its island.

Down House

Darwin wrote most of On the Origin of Species at his beloved home, Down House, in Kent, England. He generally worked in his study there.

WHAT WAS DARWIN'S CONTRIBUTION TO THE THEORY OF EVOLUTION?

Darwin's key contribution was the principle of natural selection. Three observations and inferences allowed him to deduce that natural selection is the primary driver of evolution: -the number of adults in a population tends to remain the same over time even though, the most organisms, parents tend to produce multiple and sometimes many offspring, -variation exists among members of the populations, -individuals having variation that is advantageous for survival and reproduction increase in relative frequency over time.

WHAT HAS HAPPENED SINCE DARWIN IN THE DEVELOPMENT OF OUR UNDERSTANDING OF EVOLUTION?

Gregor Mendel discovered the principles of inheritance, the basis for our understanding of how physical attributes are passed from parents to offspring. Mendel's revelation that attributes are passed as discrete units, which we now know as genes, laid the groundwork for our understanding of cell biology, our understanding of chromosomes, and eventually the field of population genetics. We now know that evolution-genetic change in a population or species-is caused by one or a combination of four forces: natural selection, mutation, gene flow, and genetic drift. We now know that each chromosome in an organism's cells consists of DNA molecules. DNA is the blueprint for all biological characteristics and functions.

Robert Hooke

Hooke did pioneering biological research using a very simple microscope. He was the first to identify cells; in fact, he coined the term cell. This illustration of cork wood cells appeared in Hooke's Micrographia (1667), the first major book on microscopy. His examinations of cells like this enabled Hooke to determine that fossils represented past life-forms.

James Hutton

Hutton (here depicted ca. 1790) founded modern geology with his theory of the earth's formation. Hutton realized that the same natural processes he observed in Scotland had occurred in the past.

Thomas Henry Huxley

Huxley (1825-1895), an English biologist, was known as Darwin's Bulldog because he so forcefully promoted Darwin's theory of evolution by natural selection. Among Huxley's contributions to evolutionary theory was the concept that humans evolved from an apelike animal.

Jean-Baptiste Lamarck

Lamarck developed an early theory of evolution involving the inheritance of acquired characteristics. Although his mechanism of evolution was wrong, Lamarck's recognition of the dynamic nature of life in the past made an important contribution to the development of evolutionary theory.

Carolus Linnaeus

Linnaeus, a botanist, zoologist, and physician, is known for his contributions to the system of classification used today by all biological scientists, including physical anthropologists. He is also thought of as one founder of modern ecology.

Charles Lyell

Lyell (here depicted ca. 1845) rediscovered Hutton's work and the idea of uniformitarianism. Lyell's research, based on examinations of geologic strata, confirmed Hutton's estimate of Earth's very old age.

Thomas Malthus

Malthus, the founder of demography, theorized that population size was limited by food supply.

Gregor Mendel

Mendel, the father of modern genetics, was a Christian monk by profession but a scientist by nature. His observations provided the foundation for our understanding of genetics.

Mendelian Inheritance

The basic principles associated with the transmission of genetic material, forming the basis of genetics, including the law of segregation and the law of independent assortment.

Malthus's five observations that inspired Darwin's theory of natural selection

observation 1: For most organisms, every pair of parents produces multiple (sometimes many) offspring. observation 2: For most organisms, the population size remains the same. No increase occurs over time. observation 3: Population is limited by the food supply. observation 4: Members of populations complete for access to food. observation 5: No two members of a species are alike in their physical attributes-variation exists. Theory Evolution by Means of Natural Selection: Individuals having variation that is advantageous for survival to reproductive age produce more offspring (and more offspring that survive) than individuals lacking this variation.