14-1 Chapter 14 Lecture Outline See PowerPoint Image Slides for all figures and tables pre-inserted into PowerPoint without notes

14-1

Chapter 14

Lecture Outline

See PowerPoint Image Slides

for all figures and tables pre-inserted into

PowerPoint without notes.

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.14-2

Evolutionary Patterns at the Species Level

Microevolution vs. macroevolution – Microevolution involves minor differences in allele

frequency between populations of the same species.

– Macroevolution involves major differences that have occurred over long periods that result in the formation of new species.

A is a group of organisms whose memspeciesbers have the potential to interbreed naturally and produce fertile offspring.


Determining if Two Populations Belong to the Same Species Using Gene Flow

Gene flow is the movement of genes. – From one generation to the next as a result of

reproduction– From one region to the next as a result of

migration If two or more populations exhibit gene flow,

– Then they are considered the same species Horses and donkeys can interbreed, but do

not experience gene flow.– Their offspring, mules, are sterile.


Hybrid Sterility


Determining if Two Populations Belong to the Same Species Using Genetic Similarity

Organisms belonging to the same species have a high degree of genetic similarity.– Similarities in DNA sequences between

individuals of two populations Suggest that gene flow has occurred recently between

those populations

Akodon dolores and Akodon molinae– Presumed to be two different species of field mice– Genetic analysis indicated that they were two

populations of the same species, living in different geographical regions.


How New Species Originate

Speciation is the process of generating new species.– Speciation has occurred continuously over the

history of life on earth.– The fossil record shows that huge numbers of

new species have originated. Most of these have gone extinct.

There are two main mechanisms of speciation.– Geographic isolation– Polyploidy


Speciation by Geographic Isolation

Geographic isolation– Occurs when a portion of a population becomes

totally isolated from the rest

If it is followed by genetic divergence– Changes in allele frequencies

Then reproductive isolation can result.– The isolated population becomes a new species.


Geographically Isolated Populations


Mechanisms of Geographic Isolation

Colonization of a distant area– A few individuals emigrate and establish a population far

from their original home.– The distance prohibits gene flow with the original

population; the new population becomes reproductively isolated.

Appearance of a geographic barrier– Uplifting of mountains, rerouting of rivers or formation of

deserts can subdivide a population.– This barrier prohibits gene flow between the divided

subpopulations; they can become reproductively isolated.


Mechanisms of Geographic Isolation

Extinction of intermediate populations– Occurs when a population that exists between other

populations dies out– Eliminates gene flow between the remaining distant

populations– The other populations can become reproductively isolated.

Speciation will only happen if the genetic changes accumulated during the period of reproductive isolation generates two populations that can no longer interbreed and make fertile offspring.


Genetic Diversity and Reproductive Isolation are Necessary for Speciation

Environmental pressures and natural selection play an important role in speciation.– After a geographical separation, the two

subpopulations will likely experience different environmental conditions.

– Different phenotypes will be selected for in each subpopulation.

– Over time, genetic differences that accumulate may result in structural, physiological and behavioral differences.

These differences may prohibit interbreeding, thus resulting in speciation.


Speciation without Geographic Barriers

Any process that leads to reproductive isolation can lead to speciation.– May not necessarily require geographic isolation

Breeding or flowering at different times of year Differences in genetically determined courtship and

mating behaviors Genetically determined incompatibility of pollen from

one species and flowers of another

– Polyploidy is the primary mechanism of speciation in the absence of geographical isolation.


Polyploidy

A condition of having multiple sets of chromosomes.– More than haploid or diploid– Can result from abnormal events in mitosis or meiosis

Chromosomes do not separate properly. Cannot mate with its original population Can self-fertilize and generate a new species

– Can result from the mating of two different species The hybrid ends up with a novel number of chromosomes. Cannot mate with either of the parent populations Can self-fertilize and generate a new species

Cotton, potato, sugarcane, broccoli, wheat, etc. are all species that resulted from polyploidy.


Speciation without Geographic Isolation


Maintaining Reproductive Isolation Between Species

New species stay reproductively isolated from other species due to mechanisms that prevent mating between species.– Reproductively isolating mechanisms


Reproductively Isolating Mechanisms

Ecological isolating mechanisms– Two populations don’t interbreed because they

occupy different niches.

Seasonal isolating mechanisms– Two populations don’t interbreed because they

mate at different times of year.

Behavioral isolating mechanisms– Two populations don’t interbreed because they

have different courtship and mating behaviors.


Reproductively Isolating Mechanisms

Mechanical isolating mechanisms– Two populations don’t interbreed because they

have incompatible genitalia. Biochemical isolating mechanisms

– Two populations don’t interbreed because their gametes are chemically incompatible.

Hybrid infertility/inviability– Two populations that can interbreed, but their

offspring are sterile or die before reproductive maturity.


Evolutionary Patterns Above the Species Level

The development of new species is the smallest irreversible unit of evolution.– After a speciation event, the new species

continues to diverge from the original species.

Several different evolutionary patterns follow speciation.


Divergent Evolution

An evolutionary pattern in which individual speciation events cause successive branches in the evolution in a group of organisms.

The evolution of horses.


Extinction

The loss of a species. Most species that have ever existed are now

extinct. Ever-changing environments leads to the

generation of new species and the elimination of others.

Divergence is accompanied by a great deal of extinction.– This is the basic pattern of evolution.– Other special patterns also exist.


Adaptive Radiation

A special evolutionary pattern Involves a rapid increase in the number of

kinds of closely related species A kind of evolutionary explosion of new

species in a short amount of time


Adaptive Radiation

Thought to occur because– A particular organism invades a previously

unexploited environment. Animals moving to land Galapagos finches

– A particular type of organism evolves a new set of characteristics that allows it to displace previously successful organisms.

Reptiles replacing amphibians


Adaptive Radiation in the Galapagos Finches


Adaptive Radiation in Terrestrial Vertebrates


Convergent Evolution

A special evolutionary pattern in which similar characteristics develop in unrelated groups of organisms– The characteristics serve a similar purpose in the

particular environment, but have very different ancestors.

Spines in desert plants Eating while flying in bats, dragonflies and swallows Body shape of whales, sharks and tuna


Convergent Evolution


Homologous and Analogous Structures

Determining if a characteristic that is similar in two different species is a result of convergent or common ancestry is important.– Homologous structures

Have different appearances and functions that arose from a common ancestor

Result from divergent evolution

– Analogous structures Have similar structures and functions but arose from

different ancestors Result from convergent evolution


Maintaining Traits through Time


Rates of Evolution

Vary greatly– From thousands to millions of years

When the environment changes rapidly– Organisms change rapidly as a result of natural

selection. High rate of speciation High rate of extinction

When the environment is stable– Organisms change very little.


Theories About the Rate of Evolution

Gradualism– The fossil record shows gradual changes in

physical features of organisms over time.– Darwin’s view of evolution by natural selection

implied gradualism. Punctuated equilibrium

– The fossil record also shows long periods of stasis.

– Argues that evolution happens in spurts of change, followed by long periods of equilibrium


Gradualism vs. Punctuated Equilibrium


The Tentative Nature of the Evolutionary History of Organisms

Tracking the evolutionary history of any given organism is difficult because most ancestral forms are now extinct.– Fossils are helpful, but the fossil record is

incomplete and provides limited amount of information about each specimen.

The likelihood of fossilization is low. Only certain types of organisms can be fossilized.

Evolutionary biologists use the information that they have to build evolutionary diagrams for groups of organisms.


An Evolutionary Diagram


Where are we on the tree?


Human Evolution

Our understanding of human evolution is based mainly on information from the fossil record.– Humans are mammals, primates, specifically

anthropoids.Hominins are humans and their human-like

ancestors.Hominids refers to hominins and African great

apes.


The Course of Human Evolution


An Overview of Human Evolution

Early primates were adapted to living in forests. As the climate became drier, grasslands replaced forests. Early hominins (Australopithecus) were adapted to living in

grasslands.– Stood upright to allow for

More rapid movement over long distances Ability to see over longer distances Freed arms for using tools, etc.

Later hominins (Homo) had larger brains and used tools.– Had larger brains and bodies– Able to use tools for a more diverse diet– Believed to have evolved at least 2.2 to 2.5 million years ago


The Origin of Homo Sapiens —Two Points of View

Out-of-Africa hypothesis– Modern humans originated in Africa from other hominin

species.– Migrated to Asia and Europe and displaced other hominin

species that had colonized those areas earlier.

Multiregional hypothesis– Homo erectus migrated and then evolved into H. sapiens. – Various subgroups of H. erectus existed throughout Africa,

Asia and Europe and interbred to give rise to the races we know today.

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14-1 Chapter 14 Lecture Outline See PowerPoint Image Slides for all figures and tables pre-inserted into PowerPoint without notes