The Evolutionary Framework of Biology

Question 1

What are “model systems,” are how are they used?

Answer 1

Because of evolutionary conservation, many characteristics are the same among species. Therefore, many simple organisms can be studied as “model systems” to understand how humans work. Such model systems might be bacteria, mice, or insects.

Question 2

What are the two important tenets of the theory of natural selection?

Answer 2

1. Reproductive rates of organisms are sufficiently high that populations would become enormous if mortality rates did not balance reproductive rates.
2. All organisms are variable and offspring are similar to their parents because they inherit their parents’ features.

Question 3

How are cetaceans an example of a gap in the fossil record?

Answer 3

Cetaceans were a gap in the fossil record until several stages in their transition from land to sea was discovered. DNA evidence shows that the existing non-cetaceans to which cetaceans are mostly closely related are hippopotami.

Question 4

Describe the current model for the progression of evolution over time.

Answer 4

The current model is called punctuated equilibrium. It differs from the previous model of gradualism (where the rate of evolution had been constant) and instead accounts for adaptive radiations, in which new adaptations can exploit new niches, which lead to adaptive radiations.

Question 5

Give an example of adaptive radiation.

Answer 5

Bats underwent adaptive radiation, leading to their abilities of flight and echolocation (the only mammals that can do so. Now, 1 out of 5 mammals are bats).

Question 6

What are the two main methods of dating fossils, and which is more common?

Answer 6

Radiometric dating (in which radioactive decay is not influenced by temperature, pressure, or other environmental variables) and K40 and Ar40 dating (more common).

Question 7

How does K40 and Ar40 dating work?

Answer 7

K40 decays to Ar40 with a half-life of about 1.26 x 10^9 years. This makes it useful for dating older fossils sandwiches between layers of volcanic rocks.

Question 8

What is artificial selection?

Answer 8

An evolutionary process whereby humans are the ones selecting for certain traits.

Question 9

Give examples of artificial selection.

Answer 9

Dog breeds that came from wolves, variations of chickens, variations of pigeons, and the variations of vegetables that came from wild cabbage through selecting for certain traits.

Question 10

Give examples of the evolutionary process of the development of resistance.

Answer 10

Bacteria to antibiotics (usually mediated by plasmids and mutations)
Viruses to immune responses (usually mediated by mutations)
Cancer cells to chemotherapeutic drugs (mediated by mutations)
Insects to pesticides (mediated by mutations)
Weeds to herbicides

Question 11

What does the term phylogenetic similarities mean?

Answer 11

It refers to commonalities between organisms that are evidence of a common ancestor and evolution. These commonalities might include morphology/anatomy like homologous limbs and vestigial organs (like the appendix and tailbone).

Question 12

What does the phrase “diversity of life” mean?

Answer 12

This phrase refers to the significant variation amongst living organisms. Fewer than 2 million species have been described, and about 9 million species of eukaryotes are estimated to exist.

Question 13

What does the phrase “unity of life” mean?

Answer 13

The fundamental unit of life in all organisms is the cell, and all cells are chemically similar. Similarly, the genes of diverse organisms are chemically identical, and biochemical processes are similar.

Question 14

How do cilia illustrate the diversity and unity of life?

Answer 14

The cilia of Paramecium and the cilia of human windpipe cells are almost identical. This demonstrates the conservation of structure and function among diverse organisms.

Question 15

What are the two unifying theories of biology?

Answer 15

Cell theory and the theory of evolution.

Question 16

What are the two basic tenets of cell theory?

Answer 16

1. All living organisms are composed of cells.
2. All cells arise from other cells.

Question 17

What are the two basic tenets of the theory of evolution?

Answer 17

1. The genetic composition of a population changes over time.
2. The process of evolution is primarily driven by natural selection, also known as descent with modification.

Question 18

Does evolution occur in the population or the individual?

Answer 18

Although natural selection occurs through interactions between individuals and their environment, individuals do not evolve; it is the population that evolves over time.

Question 19

How do soapberry bugs and balloon vine fruit illustrate natural selection?

Answer 19

Soapberry bugs that lived in a region with round fruit had on average much longer beaks for feeding on the fruit. In regions with flat fruit, the bugs had on average much shorter beaks.

Question 20

Give two examples of comparative embryology homology.

Answer 20

The pharyngeal arches and the post-anal tail.

Question 21

Study of the globin genes of multiple organisms reveals what?

Answer 21

Alignment of the genetic sequence of the globin gene reveals the differences in genetics between various organisms.

Question 22

What is convergent evolution?

Answer 22

The independent evolution of similar features in different lineages.

Question 23

Why is convergent evolution not considered to be homology?

Answer 23

Distantly-related organisms can resemble each other because of convergent evolution. Such features are not homologous; they are analogous. An example is the wings of the sugar glider and flying squirrel.

Question 24

Define biogeography.

Answer 24

The scientific study of the geographic distribution of species which accounts for geographic distances and continental drift (Pangea).

Question 25

What did studies on fruit flies reveal about humans?

Answer 25

They informed on the molecular basis of immunity.

Question 26

What did studies in giant squid reveal about humans?

Answer 26

They illuminated how nerve cells generate action potentials.

Question 27

What did studies on the marine slug, Aplysia, reveal about humans?

Answer 27

They informed on how memories are formed and stored.

Question 28

How many species have been described?

Answer 28

2 million.

Question 29

How many eukaryotic species are estimated to exist?

Answer 29

About 9 million.

Question 30

How are the genes of diverse organisms related?

Answer 30

They are all chemically identical. They use the same nucleotide bases–A, G, C, and T.

Question 31

What does the interior of the cilia of Paramecium and windpipe cells look like?

Answer 31

The interior is composed of 9 sets of doublet microtubules and a pair of singlets on the inside.

Question 32

What is a theory?

Answer 32

A theory is something that we know to be true. It is an explanation that is broader in scope than a hypothesis and supported by a large body of evidence.

Question 33

What explains the diversity of life?

Answer 33

Descendants of an ancestral organism lived in various habitats, and those populations gradually acquired modifications, or adaptations, that fit them to their specific ways of life, thus explaining the diversity of life.

Question 34

What two things do you need for evolution by natural selection?

Answer 34

1. Individuals in a population must vary in their heritable characteristics.
2. Organisms must produce more offspring than the environment can support.

Question 35

Why can’t evolution occur in a population that is genetically identical?

Answer 35

There is no variation, and therefore nothing to select for.

Question 36

What gives rise to genetic diversity?

Answer 36

Mutations and recombination.

Question 37

What four things are the basis of the scientific evidence for evolution?

Answer 37

1. Direct observations
2. Homology
3. The fossil record
4. Biogeography.

Question 38

The finches Darwin described were an example of what type of evidence for evolution?

Answer 38

The finches were an example of direct observation. Each type of finch came from a common ancestor, but on the Galapagos Islands, natural selection selected for different traits, especially in the beaks of the finches.

Question 39

What causes the similarities and differences among Earth’s many different species?

Answer 39

There is an ancient common ancestor. Species accumulate differences from their ancestors as they adapt to different environments over many generations. This can be seen with the diversity of mantids. The exterior of mantids evolved to match their surroundings, whether that be leaves, flowers, or the ground. However, their interior remained virtually the same.

Question 40

How is the wild mustard plant and its offspring an example of direct observation?

Answer 40

This example is important because it is evolution we have seen in our time. The wild mustard plant gave rise to kale, brussels sprouts, cabbage, broccoli, and kohlrabi by selecting for different traits.

Question 41

What is homology?

Answer 41

Homology describes the structures that are equivalent from an evolutionary perspective from one species to another.

Question 42

Give an example of homology in mammals.

Answer 42

Mammalian forelimbs are ancestral structures that have evolved different functions. The forelimbs of all mammals share the same arrangement of bones.

Question 43

How are genetics and genomics examples of homology?

Answer 43

Organisms share a genetic code. Many genes and biochemical pathways are conserved between species. Generally, the more closely related the species are, the more closely related their genetic sequences are.

Question 44

Why are humans more closely related to chimps than gorillas?

Answer 44

There is a 1.1% difference in the genome between humans and chimps but a 1.5% difference between humans and gorillas. Additionally, between chimps and gorillas there is a 1.6% difference.

Question 45

What is the hierarchy of the classification system biologists use to organize species?

Answer 45

Domain
Kingdom
Phylum
Class
Order
Family
Genus
Species

Question 46

Why isn’t convergent evolution considered homology?

Answer 46

Distantly-related organisms can resemble each other because of convergent evolution, which is the independent evolution of similar features in different lineages. Such features are not homologous; they are analogous. An example is the sugar glider and the flying squirrel.

Question 47

How is the fossil record a type of evidence for evolution?

Answer 47

The fossil record documents the pattern of evolution, showing how past organisms differed from present-day organisms. The fossil record also shows that many species have gone extinct. It fills gaps in the “living” record.

Question 48

How did the fossil record fill the gap for whales and cetaceans?

Answer 48

Before, there was no known mammal that resembled a whale whatsoever. However, after examining the fossil record, it was discovered that whales are related to deer and hippopotamuses because of intermediates (now extinct) found in the record. These intermediates revealed the evolution of limbs and transition of the skeleton.

Question 48

How did the fossil record fill the gap for whales and cetaceans?

Answer 48

Before, there was no known mammal that resembled a whale whatsoever. However, after examining the fossil record, it was discovered that whales are related to deer and hippopotamuses because of intermediates (now extinct) found in the record. These intermediates revealed the evolution of limbs and transition of the skeleton.

Question 49

Define biogeography.

Answer 49

Biogeography is the scientific study of the geographic distribution of species. It accounts for geographic distance and continental drift (Pangea).

Question 50

How do evolutionary trees work?

Answer 50

Each branch point represents the common ancestor of the two lineages diverging from that point. A hatch mark represents a homologous characteristic shared by all the groups to the right of the mark.