Chapter 22: Descent with Modification Flashcards
Darwin set out to explain three key observations about life. What are those three observations?
a. Organisms are well suited (adapted) for life in their environments (Here and throughout this text, the term environment refers to other organisms as well as to the physical
aspects of an organism’s surroundings.)
b. The many shared characteristics (unity) of life.
c. The rich diversity of life.
Define evolution broadly, and then give a more specific definition that came about after the
field of genetics was better understood.
Evolution is broadly defined as descent with modification, a phrase Darwin used to summarize the process by which species accumulate differences from their ancestors as they adapt to different environments over time. Evolution can also be defined as a change in the
genetic composition of a population from generation to generation
What is the pattern of evolution?
What is the process of evolution?
The pattern of evolutionary biology is revealed by data from many scientific disciplines, including biology, geology, physics, and chemistry.
The process of evolution consists of the mechanisms that produce the observed pattern
of change.
How did Aristotle (and Scala Naturae) view the origin of species?
The Greek philosopher Aristotle (384–322 A.D.) opposed any concept of evolution and viewed species as fixed and unchanging.
He believed that all living forms could be arranged on a ladder of increasing complexity (scala naturae) with perfect, permanent species on every rung.
How did the Old Testament view the origin of species?
The Old Testament account of creation held that species were individually designed by God and, therefore, perfect.
In the 1700s, many scientists viewed the adaptations of organisms as evidence that the Creator had designed each species for a purpose.
How did Carlus Linnaeus view the origin of species?
Linnaeus adopted a nested classification system, grouping similar species into increasingly inclusive categories. Linnaeus, adhering to the Old Testament belief
that all species were designed by God, did not ascribe the resemblances among species to
evolutionary kinship, but rather to the pattern of their creation.
Explain the role of fossils in rock strata as a window to life in earlier times.
Many fossils are found in sedimentary rocks formed from the sand and mud that settle to
the bottom of seas, lakes, swamps, and other aquatic habitats. New layers of sediment cover older ones and compress them into superimposed layers of rock called strata. The fossils in particular strata provide a glimpse of some of the organisms that populated Earth at the time that the layer formed.
James Hutton and Charles Lyell were geologists whose ideas strongly influenced Darwin’s
thinking. What were the ideas each of them contributed?
Often referred to as the Father of Modern Geology, Hutton proposed that Earth’s geologic features could be explained by gradual mechanisms still operating today, such as valley formed by rivers. Gradualism.
Lyell incorporated Hutton’s thinking into his principle of uniformitarianism, which states that mechanisms of change are constant over time. Lyell proposed that the same geologic processes are operating today as in the past, and at the same rate. Longtime Lyell
How would Georges Cuvier have explained the appearance of the record of life shown in
the rock strata?
First Paleontologist. He observed that the older the stratum, the more dissimilar its fossils were to current life-forms. He also observed that from one layer to the next, some new species appeared while others disappeared.
He inferred that extinction must have been a common occurrence, but he staunchly opposed the idea of evolution. He advocated catastrophism, the principle that events in the past occurred suddenly and were caused by mechanisms different from those operating in the present.
Cuvier speculated that each boundary between strata represented a catastrophe, such as a flood, that had destroyed many of the species living at that time. Such regions, he reasoned, were later repopulated by different species immigrating from other areas.
Hutton’s and Lyell’s observations and theories gave Darwin “the gift of time”. How did that influence Darwin’s thinking?
First, if geologic changes result from slow, continuous processes (gradualism) rather than sudden events, then the Earth must be far older than the few thousand estimated by theologians from biblical inference.
Second, slow and subtle processes persisting for long periods of time can also act on living organisms, producing substantial change over a long period of time.
Jean-Baptiste de Lamarck proposed a mechanism for how life changes over time. Explain the two principles of his mechanism.
use and disuse: The idea that parts of the body that are used extensively become larger
and stronger, whereas those that are not used deteriorate.
inheritance of acquired characteristics: This idea
Although Lamarck’s mechanism of evolution does not explain the changes in species over
time, his thinking has been influential. What is the importance of his ideas?
Lamarck recognized that the match of organisms to their environments can be explained by gradual evolutionary change rather than special creation.
What role did Darwin’s voyage on the HMS Beagle play in his thinking about life on
Earth?
As the ship naturalist and conversation companion to the captin, Darwin observed and collected thousands of plants and animals.
He noted that the plants and animals in temperate regions of South America more closely resembled species living in South American tropics than species living in temperature regions of Europe. Fossils he found, though clearly different from living species, distinctly resembled the living organisms of South America.
He experienced geologic change firsthand when a violent earthquake shook the coast of Chile and he observed afterward that rocks along the coast had been thrust upward
by several meters.
He also found fossils of ocean organisms high in the Andes. He inferred that the rocks containing the fossils must have been raised there by many similar earthquakes.
These observations reinforced what he had learned from Lyell: Physical evidence
did not support the traditional view that Earth was only a few thousand years old.
Darwin’s observations on the Galápagos Islands also played a role in his thinking about
life on Earth. Although the animals on the Galápagos resembled species living on the
South American mainland, more of the Galápagos species were not known from anywhere else in the world. Darwin hypothesized that the Galápagos had been colonized by organisms that had strayed from South America and then diversified, giving rise to new species on various islands.
Why are the Galápagos Islands often cited as being critical to Darwin’s development of the
idea of descent with modification?
The Galápagos Islands are a group of volcanic islands located near the equator about 900
km west of South America.
Darwin collected many types of mockingbirds, though similar to each other yet seemed to be different species. Some were unique to individual islands, while others lived on two or more adjacent islands. Furthermore, although the animals on the Galápagos resembled species living on the South American mainland, most of the Galápagos species were not known from anywhere else in the word.
Darwin hypothesized that the Galápagos had been colonized by organisms that had strayed from South America and then diversified, giving rise to new species on the various islands. With these observations, he was able to summarize his view of life: unity in life, accumulated adaptations that fit the organism’s specific ways of life, and accumulated differences of organisms can be seen.
Charles Darwin proposed that the mechanism of evolution is natural selection and that it
explains how adaptations arise. What are adaptations? Give two examples of them.
Adaptations are inherited characteristics of organisms that enhance their survival and reproduction in specific environments.
The beak size of the finches found on the Galápagos Islands - The various beaks are adapted to the specific foods available on the finches’ home islands. Some beaks are long and sharp, such as those of the common cactus finch and some beaks are narrow and pointed, such as what is found in the insect-eater, green warbler finch.
The shape and colors that the Malaysian orchid mantis has in different environments - The color and shape of the mantis closely resembles the flower on which it rests, waiting for unwary prey to come within its reach.
