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Question 1

What is the geologic timescale

Answer 1

The geological timescale is the record of Earth’s history based on geological formations and major biological events. It is divided into eras and stretches as far back as Earth has existed.

Question 2

What types of information provide the clues that scientists use in investigating evolutionary relationships?

Answer 2

Fossils, molecular techniques such as sequencing of proteins and DNA, and biogeographical studies provide the evidence that scientists use in investigating evolutionary relationships.

Question 3

What are some of the ways that fossils form?

Answer 3

Fossils form by compression, impression, the formation of casts, petrifaction, and when organisms or parts of organisms are trapped in sediments, oozing sap, or tar.

Question 4

Why will the fossil record always be incomplete

Answer 4

The fossil record will always be incomplete because most organisms never fossilize; soft-bodied organisms, for example, seldom leave fossils, and organisms that decompose or are eaten by scavengers will not leave fossils. Erosion destroys many fossils, and some fossils are buried in places that are unlikely to be sampled by fossil hunters, such as extremely deep sediments beneath ocean bottoms.

Question 5

. Distinguish between relative and absolute dating of fossils.

Answer 5

Relative dating of fossils is based upon the position of the rock stratum in which a fossil is found. It allows a paleontologist to decide whether one fossil is older or younger than another. Absolute dating assigns a range of dates that tell when a fossil formed with a direct testing method, such as carbon dating.

Question 6

How does radiometric dating work?

Answer 6

Radiometric dating analyzes the amounts of isotopes in a sample. For instance, carbon dating measures the amount of an isotope of carbon (14C) in a sample. 14C has a half-life of 5730 years. When an organism is alive, 14C is taken into its tissues at a constant proportion. When the organism dies, 14C is no longer taken in, but the 14C in the dead tissues continues to decay. The proportion of 14C to 12C therefore gradually declines. So, by measuring the amount of 14C in a sample, the age of the sample can be estimated.

Question 7

1. How have the positions of Earth’s continents changed over the past 200 million years?

Answer 7

Over the past 200 million years, Earth’s continents have drifted apart from a central, global landmass to their present positions as separate entities. They are continuing to move in different directions, riding on tectonic plates.

Question 8

How do biogeographical observations help biologists interpret evolutionary history?

Answer 8

By comparing species on isolated islands with related species from nearby mainlands, biogeographical observations help biologists to interpret the evolutionary history of species on isolated islands.

Question 9

What can homologies reveal about evolution

Answer 9

Homologous genes, chromosomes, and anatomical structures in related organisms reveal common ancestry and evolutionary relationships between species.

Question 10

What is a vestigial structure? What are some examples of vestigial structures in humans and other animals?

Answer 10

A vestigial structure is nonfunctional but homologous to functional structures in related organisms. The human appendix, human muscles that erect hairs, the tails of human embryos, and the muscles that allow us to wiggle our ears are vestigial structures. The leg bones of snakes and of whales also are also vestigial structures.

Question 11

What is convergent evolution

Answer 11

Convergent evolution is the result of similar selective pressures on unrelated organisms in similar (but not the same) environments, such that they show similar adaptations.

Question 12

. How does the study of embryonic development reveal clues to a shared evolutionary history?

Answer 12

Similar physical traits are the result of similar developmental processes, which indicate shared developmental genes inherited from a shared common ancestor.

Question 13

Why are evolutionary biologists interested in how genes influence development

Answer 13

Evolutionary biologists are interested in how homeotic genes influence development because they shed light on the genetic changes that are involved in evolution of new species from an ancestral type.

Question 14

How does analysis of DNA and proteins support other evidence for evolution?

Answer 14

Molecular analysis supports evidence for evolution because it is highly unlikely that two related species would evolve identical DNA or protein sequences. Biochemical similarities derive from a common ancestor; differences arise from mutations that occurred after two species diverged from a common ancestor. Thus, the more similar the DNA or protein sequences, the closer the evolutionary relationship.

Question 15

What is the basis of using a molecular clock to determine when two species diverged from a common ancestor?

Answer 15

The known mutation rate for a gene is the basis of using DNA as a molecular clock to determine how long ago two species diverged from a common ancestor.

Question 16

What is an advantage of using mtDNA instead of nuclear DNA in tracing evolution?

Answer 16

Using mitochondrial DNA instead of nuclear DNA in tracing evolution allows investigators to trace mothers and children. The molecular clock of mitochondrial DNA is faster than the nuclear DNA clock, so it is useful in tracing recent evolutionary events

Question 17

What hypothesis are the Grants testing, and what observations are they using to test it?

Answer 17

The Grants are testing the hypothesis that short-term, extreme, environmental changes can lead to observable changes in heritable physical traits. They observed the two main finch species (ground and cactus) on the island of Daphne Major and compared beak size and seed size after the 1977 drought and the 1983 El Niño rainy season.

Question 18

Would careful examination of finch fossils or DNA be a better way to address the questions of short-term evolution that the Grants are studying?

Answer 18

DNA would be better. Fossils are rare and might not reveal enough pattern detail over such a short period; however DNA, especially mtDNA with its faster clock, could reveal a lot.

Question 19

What types of information are used to hypothesize how species are related to one another by descent from shared ancestors? Give an example of how multiple types of evidence can support one another.

Answer 19

Paleontology, the study of fossil remains or other clues of past life, is used to make hypotheses about extinct organisms. Molecular techniques, including protein and DNA sequencing, have further enabled scientists to understand relationships among species that have descended from a common ancestor. Anatomical and developmental studies reveal the presence of homologous structures, and the study of biogeography allows scientists to determine how and when species diverged in the context of continental drift and other large-scale events.

Question 20

Compression fossil:

Answer 20

decomposed remains of plants and other organisms are preserved. For example, a leaf sinks, fine sediment covers leaf, and sedimentary rock forms.

Question 21

Impression fossil:

Answer 21

an organism presses against soft sediment, which then hardens after the organism decays, leaving an outline of the organism.

Question 22

Cast:

Answer 22

if an imprint is later filled with mud that hardens into rock, the resulting cast is a rocky replica of the ancient organism.

Question 23

Petrifaction

Answer 23

an organism dies, decays, and is buried. Water containing dissolved minerals seeps through, and the organic matter that is replaced by minerals “turns to stone.”

Question 24

Intact preservation:

Answer 24

sticky tree resin entraps plants and animals, hardening them in amber tombs.

Question 25

Trace fossils: feces or animal tracks may be preserved as evidence of an organism’s movements or behavior.

Answer 25

feces or animal tracks may be preserved as evidence of an organism’s movements or behavior.

Question 26

Why don’t all organisms Leave Fossils

Answer 26

Organisms do not always leave fossils when they die. Their bodies may be too soft to be preserved, or they may be decomposed or eaten after death. In addition, even fossils that do form may be destroyed by erosion, or they may form in areas where no one is likely to discover them.

Question 27

Why is the fossil record useful, even if it doesn’t represent every type of organism that ever lived?

Answer 27

Although not every species is represented in the fossil record, it does reveal a sample of species that lived in the past and are now extinct. In addition, the fossil record allows scientists to better understand evolutionary relationships among species and why some species were adapted to a given environment. The fossil also record gives clues as to what the environmental conditions were like at a particular time, which are important in determining what other organisms could have existed during the time period being studied.

Question 28

Index fossils represent organisms that were widespread but lived during relatively short periods of time. How are index fossils useful in relative dating?

Answer 28

Since the index fossil lived for a short period, if one is found in association with a fossil of unknown date, the index fossil can provide a narrow range of relative dates for the unknown fossil.

Question 29

Why can’t scientists use potassium–argon dating on a preserved woolly mammoth that died 20,000 years ago?

Answer 29

The half-life of 40K is 1.3 billion years, far too long to date fossils from an animal that died only 20,000 years ago. Potassium-argon dating is appropriate for fossils 300,000 years or older.

Question 30

How do molecular sequences provide different information than relative and absolute dating?

Answer 30

Relative dating and absolute dating provide the ages of fossils; however, molecular sequences provide information about dates for the appearance of mutations in a population and dates for speciation events.

Question 31

How have geological events such as continental movements and the emergence of new volcanic islands influenced the history of life on Earth?

Answer 31

Continental movements and the emergence of new volcanic islands provide opportunities for allopatric speciation. Long ago, all the continents were joined as one super-continent known as Pangaea. However, species were split up when the continents separated. Once-uniform populations soon diverged as selective pressures changed. Similarly, as organisms colonized isolated volcanic islands, the new selective pressures selected for new adaptations, which eventually led to the formation of new species.

Question 32

Why is it important for evolutionary biologists to be able to distinguish between homologous and analogous anatomical structures?

Answer 32

If two structures are termed homologous then there are similarities between them that reflect a common ancestry. Analogous structures appear superficially similar, but the structures have evolved independently.

Question 33

Provide examples of homologous and analogous structures other than those mentioned in this chapter.

Answer 33

The wings of a bird and of a fly are analogous; both function in flight, but the embryonic origin is different. The wing of a bird and the foreleg of a frog are homologous structures; their embryonic origin is similar.

Question 34

The giant anteater lives in South America, the scaly anteater lives in tropical parts of Asia and Africa, and the spiny anteater lives in Australia. The three animals are not at all closely related, but they resemble each other closely. They have long, sticky tongues that they use to eat ants, no teeth, large salivary glands, and long, bald snouts. Which phenomenon do these animals illustrate?

Answer 34

These animals illustrate convergent evolution since their physical traits closely resemble each other without a common ancestor connection. They have evolved similar adaptations in response to similar environmental selective pressures.

Question 35

How did the discovery of homeotic genes help launch the new field of “evo-devo

Answer 35

Homeotic genes help explain how a few small mutations in key developmental genes can have profound phenotypic effects, and how evolutionary events can occur in short periods of time.

Question 36

Suggest a type of genetic change that could have a drastic effect on the evolution of a species.

Answer 36

A mutation in a homeotic gene could bring about new body plans, which could have a drastic effect on evolution.

Question 37

How do biologists use sequences of proteins and genes to infer evolutionary relationships?

Answer 37

All species use the same four DNA nucleotides and the same 20 amino acids, and many genes and proteins only have minor differences from one species to another. It’s unlikely that two unrelated species would evolve precisely the same DNA and protein sequences. Therefore, it is logical to surmise that the greater the molecular similarities, the more closely related the species.

Question 38

Scientists have extracted flu viruses from people who died in the 1918 influenza epidemic. How could genetic sequences from these viruses be useful today?

Answer 38

Genetic sequences from each of these flu viruses would provide a mutation history that could help scientists understand the evolutionary history of the flu virus and how to better combat it.

Question 39

Why is the DNA sequence of one gene a less accurate indicator of the evolutionary relationship between two species than a comparison of large portions of the two genomes?

Answer 39

One gene may or may not mutate rapidly. Comparing large portions of two genomes gives a more general view of the overall rate of evolutionary divergence between the species.

Question 40

Some genes are more alike between human and chimp than other genes are from person to person. Does this mean that chimps are humans or that humans with different alleles are different species? What other explanation fits the facts?

Answer 40

No. Although chimps and humans share a common ancestor (and therefore share many genes), they are reproductively isolated from one another so they are different species. Genes that are very similar between humans and chimps may be the most important genes (that is, mutations in those genes may be fatal, slowing their rate of change). Genes that vary within a population may not be essential to survival or may have mutated after the two species diverged from the common ancestor.

Question 41

If scientists could extract DNA from dinosaur fossils, how could they use the sequence to learn more about the origin of birds?

Answer 41

Besides using the DNA to confirm relationships within the clade, it could also be useful in learning more about specific events in reptile evolution. For example, the dinosaur fossil DNA could reveal a particular gene that mutated and gave a selective advantage to birds.

Question 42

Birds normally lack teeth, but scientists have discovered a mutant chicken embryo with a mouth full of teeth resembling those of alligators. They subsequently found that a mutation in one gene was responsible for the toothy bird. How does this finding provide evidence for evolution?

Answer 42

The finding shows that chickens and alligators share a similar gene and common ancestry, but that one key mutation to the tooth gene occurred after birds split off from the other reptiles.

Question 43

Why are molecular clocks useful, and what are their limitations?

Answer 43

If biologists know the mutation rate for any gene, plus the number of differences in the DNA sequences for that gene in two species, they can use the DNA as a molecular clock to estimate the time when the organism diverged from a common ancestor. One limitation is that not all DNA sequences mutate at the same rate.

Question 44

Evolutionary biologists often try to assign an approximate date when two organisms last shared a common ancestor. Why do you think that molecular evidence often yields an earlier date than fossil evidence?

Answer 44

Molecular evidence would be apparent from approximately the point of mutation. Physical evidence in the form of a fossil would have to rely on expression of the mutation in an organism that died under just the right circumstances to be fossilized. Since this is a rare event, the likelihood of its happening right after the mutation’s appearance is slim.

Question 45

Genetic anthropology combines the study of DNA with physical evidence such as fossils to reveal the history of the human species. Use the Internet to research the goals and methods of the Genographic Project, HapMap, or the Human Genome Diversity Project. What are the benefits of these projects? Can you see any ethical issues arising from this type of research?

Answer 45

The Genographic Project is trying to map the migration patterns of humans from our last common ancestral population to today. It uses DNA samples from hundreds of thousands of volunteers around the world and analyzes it with sophisticated software programs. The HapMap project is looking at genetic similarities and differences among people around the world to look for DNA sequences of genetic diseases. The DNA samples are donated anonymously from four populations. The Human Genome Diversity Project collects cell lines from individuals around the world, documenting the genetic diversity in the human population and making the DNA available to researchers. Benefits could include better understanding of many diseases, how different populations got to where they are today geographically, and relationships between different population groups. Ethical issues could include misuse of individual’s DNA information, stigmatizing groups based on genetic information discovered, or interference with established religious or cultural explanations of origins.

Question 46

Search the Internet for a copy of the Declaration of Independence. Look for words that were spelled differently in 1776 compared to today’s spelling. How are changes in language similar to evolutionary changes? How are they different?

Answer 46

Like changes to DNA, changes to spelling and language are random and come from a change to an original template. Spelling changes accumulate in the language as mistakes are made in copying information. While many alternative spellings may appear, not all are selected for and remain in the language. One could also argue that American English evolved from British English in a manner similar to a founder effect. It is also possible to trace the history of a population through the changes to its language. However, unlike evolutionary changes, changes to spelling and language have more latitude. Spellings can drastically change (e.g. “logique” to “logic”) yet still leave the word recognizable and serving the same function.

Question 47

What are some examples of each line of evidence for evolution?

Answer 47

Fossils of bivalve shells that do not exist today show us that there were once species with different morphology than there are today. Radiometric dating could indicate that the fossil is 200 million years old..
The similarity of species in geographical regions that were once connected, like in Chile and New Zealand, suggests that those species were once part of a united population and have now changed enough to be categorically distinct.
The anatomical similarity of butterflies and moths suggest they share a common ancestor. Their wing structures are homologous. So, moths and butterflies may have evolved from a common ancestral species.
The early stages of embryonic development by mammals are very similar; an early embryonic mouse looks very similar to the early stage of a human. This supports the notion that mammals are all derived from a common ancestor.. This is further supported by the genetics involved in coordinating those early embryonic events. The genes involved in these processes are strongly conserved in mammals, meaning they share very similar sequences.