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UNIT 4: EVOLUTION
Biology: A Global Approach (12th edition)
Contents:
Chapter 21: How evolution works?
Chapter 22: Phylogenetic reconstruction
Chapter 23: Microevolution
Chapter 24: Species and speciation
Chapter 25: Macroevolution
Vliet, L. van (Lenore)
09/2021
, Lenore van Vliet - 2988631
21. How evolution works
21.1 THE DARWINIAN REVOLUTION CHALLENGED TRADITIONAL VIEWS OF A YOUNG
EARTH INHABITED BY UNCHANGING SPECIES
Endless forms most beautiful
Shared features illustrate the unity of life, since all organisms share characteristics, Darwin’s theory
illustrated 3 key points:
1. Organisms are well suited for life in their environments
2. The many shared characteristics of life
3. The rich diversity of life
Darwin eventually concluded that life evolves over time!
Evolution = descent with modification
Or also known as change in the genetic composition of a population from generation to generation.
This can be related to two ways we can look at evolution:
Pattern --> data from many different disciplines
Process --> the mechanisms that cause the observed pattern of change = representing the
natural causes of the natural phenomena we observe.
The power of evolution as a unifying theory is its ability to explain and connect a vast array of
observations about the living world.
--> This theory continues to be tested by examining whether or not it can account for new
observations and experimental results.
Scala naturae and classification of species
- Aristotle => recognized certain affinities among organisms and concluded that life-forms
could be arranged on a ladder of increasing complexity later known as the Scala naturae.
- Linnaeus => developed a two part/binomial system for naming species using a nested
classification system, but he did not ascribe the resemblances among species.
- Cuvier => observed that from one layer of stone to the next species disappeared and
appeared. Coming to the conclusion that extinctions are common because each boundary
between strata represents a sudden catastrophic event.
- Hutton => proposed that earth’s geologic features could be explained by gradual
mechanisms.
- Lyell => Used Hutton’s thinking to state that the same geologic mechanisms are operating
today as in the past and at the same rate.
- Lamarck => proposed that life evolves as environments change
Ideas about change over time
Fossils (= the remains or traces of organisms from the past) contain a lot of evolutionary data that
Darwin could use for his theory of evolution through natural selection, agreeing that if geologic
change results from slow continuous processes rather than sudden events, then earth must be much
older than the widely accepted age of a few thousand years.
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, Lenore van Vliet - 2988631
Lamarck’s hypothesis of evolution
The incorrect mechanism Lamarck proposed is what he is most well-known for: He compared living
species with fossil forms and explained his findings using two principles widely accepted during his
time:
--> Use and disuse = the idea that parts of the body that are used extensively become larger
and stronger, while those that are not used deteriorate.
--> Inheritance of acquired characteristics = an organism could pass modifications to its
offspring.
This led to Lamarck concluding that evolution happens because organisms have an innate drive to
become more complex.
Darwin rejected this idea but he did agree that variation was introduced into the evolutionary
process in part by inheritance of acquired characteristics.
21.2 DESCENT WITH MODIFICATION BY NATUR AL SELECTION EXPLAINS THE
ADAPTATIONS OF ORGANISMS AND THE UNITY OF LIFE
Darwin went on a voyage around the world during which he found fossils of ocean organisms high in
the Andes, and this reinforced what he had learned from Lyell: physical evidence did not support the
traditional view that the earth was only a few thousand years old.
Many examples of adaptations and inherited characteristics of organisms that enhance survival and
reproduction in specific environments, which led him to ask the question: Could a new species arise
from an ancestral form by the gradual accumulation of adaptations to a different environment?
Darwin realized that explaining adaptations was essential to understanding evolution. His
explanation of how adaptations arise centered on natural selection (= a process in which individuals
that have certain inherited traits tent to survive and reproduce at higher rates than do other
individuals because of those traits).
--> Darwin’s book: The origin of species and its proponents have convinced most scientists
that life’s diversity is the product of evolution.
Ideas from the origin of species
Natural selection explains three broad observations about nature: the unity of life, the diversity of
life and the striking ways in which organisms are suited for life in their environments.
- Descent with modification = Darwin’s view of life --> As the descendants of an ancestral
organism lived in various habitats they gradually accumulated diverse modifications or
adaptations that fit them to specific ways of life.
It has led to the rich diversity of life, so he figured that the history of life can be viewed as a
tree with multiple branching’s from a common trunk.
- Artificial selection, natural selection and adaptation = Humans have modified species over
many generations by selecting and breeding individuals that possess desired traits (=
artificial selection)
Darwin stated that a similar process occurs in nature:
Observation 1: members of a population often vary in their inherited traits
Observation 2: all species can produce more offspring than their environment can
support and many of these offspring fail to survive and reproduce.
Inference 1: individuals whose inherited traits give them a higher probability of
surviving and reproducing in a given environment tend to leave more
offspring than do other individuals.
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