1. 17-4 Patterns of Evolution
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Macroevolution
Macroevolution refers to large-scale evolutionary patterns and processes that occur over long periods of time.
Six important topics in macroevolution are:
extinction
adaptive radiation
convergent evolution
coevolution
punctuated equilibrium
changes in developmental genes
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Extinction
Extinction
More than 99% of all species that have ever lived are now extinct.
In the past, most researchers looked for a single, major cause for each mass extinction.
Many paleontologists now think that mass extinctions were caused by several factors.
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4. Extinctions
Occur because species compete for resources and environments change (natural selection).
Mass extinctions wiped out entire ecosytems. Food webs collapsed and disrupted energy flow through the biosphere.
Most mass extinctions caused by several factors.
Large volcanoes erupting, continents moving, sea levels changing.
Leads to burst of evolution as species fill niches.

5. Mass extinctions
Five or six mass extinctions of many species and higher taxonomic groups
Major climate changes
Catastrophes such as asteroid impacts

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Extinction
What effects have mass extinctions had on the history of life? Mass extinctions have:
provided ecological opportunities for organisms that survived
resulted in bursts of evolution that produced many new species
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Adaptive Radiation
Adaptive Radiation
Adaptive radiation is the process by which a single species or a small group of species evolves into several different forms that live in different ways.
For example, in the adaptive radiation of Darwin's finches, more than a dozen species evolved from a single species.
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Adaptive Radiation
All mass extinctions have been followed by periods of recovery known as adaptive radiations.
After almost every mass extinction, numerous new species have evolved to fill new or vacated ecological niches in the changed environment.
The extinction of dinosaurs, for example, was followed by an explosive rise of mammals.
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Adaptive Radiation
Adaptive Radiation of Mammals
Artiodactyls
Cetaceans
Perissodactyls
Tubulidentates
Hyracoids
Sirenians
Proboscideans
This diagram shows part of the adaptive radiation of mammals, emphasizing current hypotheses about how a group of ancestral mammals diversified over millions of years into several related living orders. Note that the dotted lines and question marks in this diagram indicate a combination of gaps in the fossil record and uncertainties about the timing of evolutionary branching.
Ancestral Mammals
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Convergent Evolution
Convergent Evolution
Different organisms undergo adaptive radiation in different places or at different times but in similar environments.
The process by which unrelated organisms come to resemble one another is called convergent evolution.
The organisms face similar environmental pressures. Natural selection molds different body structures into modified forms (arms and legs into wings and flippers).
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13. Biogeography of Mammals
Convergent Evolution in Mammals
Nine-Banded Armadillo
Chinese Pangolin
Similar ecological opportunities on different continents have resulted in convergent evolution among these and other mammals. Mammals that feed on ants and termites evolved not once but five times in different regions. Powerful front claws; a long, hairless snout; and a tongue covered with sticky saliva are common adaptations in these insect-eating animals.
Common Echidna
Giant Anteater
Aardvark
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Convergent Evolution
Structures that look and function similarly but are made up of parts that do not share a common evolutionary history are called analogous structures.
A dolphin’s fluke and a fish’s tail fin are analogous structures.
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15. Convergent evolution can produce outwardly similar structures that differ anatomically. The wings of (a) insects and (b) birds and the sleek, streamlined shapes of (c) seals and (d) penguins are examples of such analogous structures.

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Coevolution
Coevolution
Sometimes organisms that are closely connected to one another by ecological interactions evolve together.
The process by which two species evolve in response to changes in each other over time is called coevolution.
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Bumblebees and the flowers they pollinate have coevolved so that both have become dependent on each other for survival.
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18. Punctuated Equilibrium
Gradualism
Darwin felt that biological change was slow and steady, an idea known as gradualism.
Biologists have considered two different explanations for the rate of evolution, as illustrated in these diagrams. Gradualism involves a slow, steady change in a particular line of descent. Punctuated equilibrium involves stable periods interrupted by rapid changes involving many different lines of descent.
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19. Punctuated Equilibrium
Fossil records show that some organisms evolved gradually over time - gradualism
Others are in equilibrium – have changed little over time.
Long, stable periods are interrupted by brief periods of more rapid change – punctuated equilibrium. May occur when
a small population becomes isolated from the main part of the population or a small group migrates to a new environment.
a mass extinction occurs.
Organisms evolve rapidly to fill available niches.

20. Punctuated Equilibrium
Punctuated equilibrium is a pattern of evolution in which long stable periods are interrupted by brief periods of more rapid change.
Biologists have considered two different explanations for the rate of evolution, as illustrated in these diagrams. Gradualism involves a slow, steady change in a particular line of descent. Punctuated equilibrium involves stable periods interrupted by rapid changes involving many different lines of descent.
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22. Punctuated Equilibrium
The concept of punctuated equilibrium has generated debate and is still controversial among some biologists today.
Evolution has often proceeded at different rates for different organisms at different times during the history of life on Earth.
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24. Developmental Genes and Body Plans
It is suspected that changes in genes for growth and differentiation during embryological development could produce changes in body shape and size.
Small changes in the activity of control genes can affect many other genes to produce large changes in adult animals.
These master control genes are Hox genes.
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25. Developmental Genes and Body Plans
Evolution of Wings in Insects
Ancient Insect
Two Types of Modern Insects
Some ancient insects, such as the mayfly nymph (top), had winglike structures on many body segments. Modern insects have only four wings or two wings. Changes in the expression of developmental genes may explain how these differences evolved.
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26. Developmental Genes and Body Plans
Small changes in the timing of cell differentiation and gene expression can make the difference between long legs and short ones.
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17-4
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17-4
Darwin's species of finches were very similar but different in beak size and feeding habits. This is an example of
convergent evolution.
coevolution.
adaptive radiation.
stabilizing selection.
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17-4
A slow steady change in a particular line of descent is called
coevolution.
gradualism.
punctuated equilibrium.
convergent evolution.
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17-4
Master control genes are called
hox genes.
developmental genes.
embryonic genes.
regulatory genes.
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17-4
Some evidence suggests that species do not change much over long periods of time and then undergo relatively short periods of rapid speciation. This kind of change is called
coevolution.
genetic equilibrium.
adaptive radiation.
punctuated equilibrium.
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17-4
Fossil evidence shows that mass extinctions
ended the existence of many species in a short period of time.
occurred mainly when the dinosaurs disappeared.
require an asteroid strike to occur.
caused convergent evolution among animals.
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