Chapter 20

Question 1

Vestigial Structure

Answer 1

An anatomical feature of living organisms that no longer retains its function.

Question 2

Catastrophism

Answer 2

The theory that Earth has been affected by sudden, violent events that were sometimes world-wide in scope and that each layer of fossils represented the remains of organisms that had died in a local catastrophe such as a flood. Somewhat different species then recolonized the area, and when another catastrophe struck, they formed a different set of fossils in the next higher layer.

Question 3

Inheritance of Acquired Characteristics

Answer 3

Changes that an animal aquires during its lifetime are inherited by its offspring.

Question 4

Describe J. B. de Lamarck’s role as the first person in recent times to suggest biological evolution.

Answer 4

According to his principle of use and disuse, body parts grow in proportion to how much they are used, unused structures get weaker and shrink.

According to his second principle, the inheritance of acquired characteristics, changes that an animal acquires during its lifetime, are inherited by its offspring.

Despite the shortcomings of his theory, Lamarck made four important contributions to the development of an evolutionary world-view:

1. He proposed that all species change through time.
2. He recognized that changes are passed from one generation to the next.
3. He suggested that organisms change in response to their environments.
4. He hypothesized the existence of specific mechanisms that caused evolutionary change.

Question 5

Gradualism

Answer 5

The view that Earth and its living systems changed slowly over its history.

Question 6

Uniformitarianism

Answer 6

The concept that the geologic processes that sculpted Earth’s surface over long periods of time—such as volcanic eruptions, earthquakes, erosion, and the formation and movement of glaciers—are exactly the same as the processes observed today.

Question 7

Explain why Lamarck’s proposed mechanism of evolution is no longer accepted.

Answer 7

Although muscles do grow larger through continued use, most structures do not respond in the way Lamarck predicted. Structural changes acquired during an organism’s lifetime are not inherited by the next generation.

Question 8

Artificial Selection

Answer 8

Selective breeding of animals or plants to ensure that certain desirable traits appear at higher frequency in successive generations.

Question 9

Natural Selection

Answer 9

The evolutionary process by which alleles that increase the likelihood of survival and the reproductive output of the individuals that carry them become more common in subsequent generations.

Question 10

Describe Darwin’s theory of evolution by natural selection and A. R. Wallace’s contribution.

Answer 10

Wallace had the same ideas at the same time but Darwin got published.

Question 11

Descent with Modification

Answer 11

Biological evolution.

Question 12

Biological Evolution

Answer 12

The process by which some individuals in a population experience changes in their DNA and pass those modified instructions to their offspring.

Question 13

Radiometric Dating

Answer 13

A dating method that uses measurements of certain radioactive isotopes to calculate the absolute ages in years of rocks and minerals.

Question 14

Describe carbon dating.

Answer 14

Fossils that still contain organic matter, such as the remains of bones or wood, can be dated directly by measuring the amount of the isotope 14C.

Living organisms absorb traces of 14C and large quantities of the stable 12C from the environment and incorporate them into biological molecules. As long as an organism is still alive, its 14C content remains constant because any 14C that decays is replaced by the uptake of other 14C atoms. But as soon as the organism dies, no further replacement occurs, and 14C begins its steady radioactive decay.

Scientists use the ratio of 14C to 12C present in a fossil to determine its age.

Question 15

Plate Tectonics

Answer 15

The geologic theory describing how Earth’s crust is broken into irregularly shaped plates of rock that float on its semisolid mantle.

Question 16

Continental Drift

Answer 16

The long-term movement of continents as a result of plate tectonics.

Question 17

Pangea

Answer 17

A single supercontinent present 250 million years ago that resulted from all of the tectonic plates coalescing together.

Question 18

Laurasia

Answer 18

The northern continent that resulted from the splitting of Pangea.

Question 19

Gondwana

Answer 19

The southern continent that resulted from the splitting of Pangea.

Question 20

Continuous Distribution

Answer 20

A geographic distribution in which a species lives in suitable habitats throughout a geographic area.

Question 21

Disjunct Distribution

Answer 21

A geographic distribution in which populations of the same species or closely related species live in widely separated locations.

Question 22

Dispersal

Answer 22

The movement of organisms away from their place of origin.

Question 23

Vicariance

Answer 23

The fragmentation of a continuous geographic distribution by nonbiological factors.

Question 24

Biota

Answer 24

The total collection of organisms in a geographic region.

Question 25

Biogeograpgic Region

Answer 25

A major region of Earth that is occupied by distinct evolutionary lineages of plants and animals.

The 8 regions are: Nearctic, Neotropical, Palearctic, Oriental, Ethiopian, and Australian.

Question 26

Endemic Species

Answer 26

A species that occurs in only one place on Earth.

Question 27

Convergent Evolution

Answer 27

The evolution of similar adaptations in distantly related organisms that occupy similar environments.

Question 28

Cladogenesis

Answer 28

The evolution of two or more descendant species from a common ancestor.

Question 29

Anagenesis

Answer 29

The slow accumulation of evolutionary changes in a lineage over time as it adapts to changing environments. If morphological changes are large, the organisms may have different names at different times in their history.

Question 30

Gradualist Hypothesis

Answer 30

The hypothesis that large changes in either geologic features or biological lineages result from the slow, continuous accumulation of small changes over time.

Question 31

Punctuated Equilibrium Hypothesis

Answer 31

The evolutionary hypothesis that most morphological variation arises during speciation events in isolated populations at the edge of a species’ geographic distribution.

Question 32

Macroevolution

Answer 32

Large-scale evolutionary patterns in the history of life, producing major changes in species and higher taxonomic groups.

Question 33

Cope’s Rule

Answer 33

Organisms tend to increase in body size over evolutionary time.

Question 34

Preadaptation

Answer 34

A characteristic evolved by an ancestral species that serves an adaptive but different function in a descendant species or population.

Preadaptations are said to occur when a trait that is adaptive in one context is also advantageous in another. In this situation, the trait may be enhanced by natural selection, modifying and enhancing the feature to enhance its new function. Such preadaptations are lucky accidents; they never evolve in anticipation of future evolutionary needs.

Question 35

Allometric Growth

Answer 35

Allometric growth occurs when there are differential growth rates of different parts of the body during development. In closely related species, allometric growth can lead to significant morphological changes. The same body part may be much larger in one species than in another.

Question 36

Heterochrony

Answer 36

Changes in the relative rate of development of morphological characters.

Question 37

Pedomorphosis

Answer 37

A common form of heterochrony in which juvenile characteristics are retained in a reproductive adult.

Question 38

Neoteny

Answer 38

A form of heterochrony that occurs when larvae acquire the ability to reproduce.

Question 39

Evolutionary Developmental Biology

Answer 39

A field of biology that compares the genes controlling the developmental processes of different animals to determine the evolutionary origin of morphological novelties and developmental processes.

Question 40

Homeotic Genes

Answer 40

Regulatory genes that code for transcription factors that bind regulatory sites on DNA, either activating or repressing the expression of other genes that contribute to an organism’s form.

Question 41

Hox Genes

Answer 41

Genes in the Hox family control the overall body plan of animals. Hox genes always include a 180-nucleotide sequence (a homeobox) that codes for a homeodomain, part of a protein that functions as a transcription factor. When bound to a regulatory site on a strand of DNA, the homeodomain either activates or represses a downstream gene involved in development.

Question 42

Homeobox

Answer 42

A region of a homeotic gene that corresponds to an amino acid section of the homeodomain.

Question 43

Homeodomain

Answer 43

An encoded transcription factor of each protein that binds to a region in the promoters of the genes whose transcription it regulates.

Question 44

What is the Pax-6 gene?

Answer 44

The Pax-6 gene is a highly conserved and widely distributed gene that triggers activity in genes that carry the specific instructions for making an eye typical of the species. So even if you take the gene from on animal to the other, it will code for eyes typical to the organism it is in.

Question 45

Explain the crucial influence of continental drift on evolution and biogeography.

Answer 45

Pangea’s breakup was a powerful vicariant experience for species that were widespread in the Mesozoic. The subsequent geographic isolation of continents fostered the evolution of distinctive regional biotas (all organisms living in a region).

Drifting continents induced global changes in Earth’s climate. The movement of continents toward the poles encouraged the formation of glaciers, which caused temperature and rainfall to decrease world-wide. Earth’s average temperature has fluctuated widely because of complex continental movements. These changes greatly changed life on the planet.

Question 46

Explain why a similar morphology of two groups of organisms is not necessarily indicative of a close biological relationship between the two.

Answer 46

Under similar environmental pressures and lifestyles, similar structures are favoured by natural selection. Therefore, structures may be morphologically similar even among unrelated species. Their overall resemblance is the product of convergent evolution, the evolution of similar adaptations in distantly related organisms that occupy similar environments.

Question 47

Recall the conditions necessary for fossilization, and explain why fossilization is a rare event.

Answer 47

Conditions of low oxygen or high acidity are ideal for fossilization. Hard structures such as skeletons and teeth do not readily decompose and are more often fossilized than softer structures. Some fossils are casts or moulds; in others, the original materials are replaced by dissolved minerals. The availability of fossils is highly skewed toward certain areas, certain organisms, or parts of organisms.

Question 48

What are the general functions of tool-kit genes? How can species with the same tool-kit genes have different morphologies?

Answer 48

Hox and Pax genes are examples of tool-kit genes. Tool-kit genes control the development of the body plan through regulation of the timing and amount of expression of many other genes important in the development of particular structures. Tool-kit genes may have different levels of activity at different times, leading to a different sequence of development and different morphology.