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Chapter 15: Evolution…What is it?
Name: ____________________________
1. Simple definition = _____________________________________
Fossils shape ideas about evolution:
2. When evidence indicated that Earth was much older than many people had thought, biologists
began to suspect that species change over time, or _______________.
3. _________________ are an important source of evolutionary evidence because they provide a
record of early life and evolutionary history.
1831: Enter Charles Darwin
Son of wealthy parents; Lead a privileged life; Dropped out of medical school; Enjoyed walking in
nature & collecting beetles
The Voyage that Changed the World
4. ____________________ sailed around the world on a ____ year voyage. At the age of _____,
Darwin soon became the ship’s naturalist.
What Darwin Observed on the Voyage
5. ______________ animals were similar to animals today.
6. Fossil seashells found high in mountains.
7. ____________________ can lift the land several feet at a time.
8. Life is _______________ to specific habitats.
9. There is much _________________ in populations within each generation.
Darwin’s “Theory” of Evolution has many components
10. _____________________, _______________________, __________________________
Malthus’ Contentions
11. English economist Thomas _______________ had proposed an idea that Darwin modified and
used in his explanation.
12. Malthus’s idea was that the __________________________________________________ and
nature would intervene through starvation, disease and war.
Darwin’s Insight…Natural Selection
13. Animal populations grow faster than food supplies…
14. Members of each generation must ________________ for limited resources…
15. ______________________ members have traits that gave them an advantage in competition…
16. ___________________________ those traits that are successful under the present conditions.
Darwin continues his studies
Darwin observed that the traits of individuals vary in populations. Variations are then inherited.
17. Breeding organisms with specific traits in order to produce offspring with identical traits is
called _____________________________________.
Darwin hypothesized that there was a force in nature that worked like artificial selection.
18. __________________________________ is a mechanism for change in populations.
19. Species are not fixed but rather change _________________over time.
20. Natural selection works on the _________________________________ in each population.
21. As differences build up over time _________________________ arise. Therefore, different
species have common ancestors in time.
Adaptations: Evidence for Evolution
22. ____________ = Any variation that aids an organism’s chances of survival in its environment.
Adaptation: Mimicry
23. ________________ is a structural adaptation that enables one species to resemble another
species. A harmless species has adaptations that result in a physical resemblance to a harmful
species. Predators that avoid the harmful looking species also avoid the similar-looking
harmless species. Also, two or more harmful species can resemble each other.
Adaptation: Camouflage
24. __________________ = An adaptation that enables species to blend with their surroundings.
Because well-camouflaged organisms are not easily found by predators, they survive to reproduce.
Physiological Adaptations
25. ___________________________________ are changes in an organism’s metabolic processes.
In addition to species of bacteria, scientists have observed these adaptations in species of insects
and weeds that are pests.
Anatomy: Evidence for Evolution
26. Structural features with a common evolutionary origin are called
27. Homologous structures can be ___________________________________________________.
28. The body parts of organisms that do not have a common evolutionary origin but are similar in
________________ are called _______________________________________________.
For example, insect and bird wings probably evolved separately when their different ancestors
adapted independently to similar ways of life.
29. A _____________________________________ is a body structure in a present-day organism
that no longer serves its original purpose, but was probably useful to an ancestor.
Embryology: Evidence for Evolution
30. An embryo is the earliest stage of growth and development of both plants and animals.
The embryos of a fish, a reptile, a bird, and a mammal have a tail and pharyngeal pouches.
Biochemistry: Evidence for Evolution
31. Nearly all organisms share ________________________________________________ among
their biochemical molecules.
Organisms that are biochemically similar have fewer differences in their amino acid sequences.
Today, scientists combine data from fossils, comparative anatomy, embryology, and biochemistry
in order to interpret the evolutionary relationships among species.
Populations, not individuals, evolve
Evolution occurs as a population’s genes and their frequencies change over time.
32. Picture all of the alleles of the population’s genes as being together in a large pool called a
33. The percentage of any specific allele in the gene pool is called the
34. They refer to a population in which the frequency of alleles remains the same over generations
as being in ____________________________________________.
Changes in Genetic Equilibrium
35. A population that is in genetic equilibrium is _________________________.
36. Any factor that affects the genes in the gene pool can change __________________________,
disrupting a population’s genetic equilibrium, which results in the process of evolution.
37. One mechanism for genetic change is _______________. Environmental factors, such as
radiation or chemicals, cause many mutations, but other mutations occur by chance.
38. Another mechanism that disrupts a population’s genetic equilibrium is
________________________—the alteration of allelic frequencies by chance events.
Genetic equilibrium is also disrupted by the movement of individuals in and out of a population.
39. The transport of genes by migrating individuals is called ____________________.
3 Types of Natural Selection
40. ______________________, ________________________, _________________________
41. Draw 3 curves
The Evolution of Species
42. The evolution of new species, a process called ___________________ occurs when members
of similar populations no longer interbreed to produce fertile offspring within their natural
In nature, physical barriers can break large populations into smaller ones.
43. ______________________________ occurs whenever a physical barrier divides a population.
Reproductive Isolation can result in Speciation
44. ________________________________________ occurs when formerly interbreeding
organisms can no longer mate and produce fertile offspring.
45. The ___________________ material of the populations can become so different that
fertilization cannot occur. Another type of reproductive isolation is __________________.
Speciation Rates
46. _________________ is the idea that species originate through a gradual change of adaptations.
47. In 1972, Niles Eldredge and Stephen J. Gould proposed a different hypothesis known as
This hypothesis argues that speciation occurs relatively quickly, in rapid bursts, with long periods
of genetic equilibrium in between.
Diversity in New Environments
48. When an ancestral species evolves into an array of species to fit a number of diverse habitats,
the result is called _____________________________________.
49. Adaptive radiation is a type of ______________________________________, in which
species that were once similar to an ancestral species become increasingly different.
50. A pattern of evolution in which distantly related organisms evolve similar traits is called
This occurs when unrelated species occupy similar environments in different parts of the world.