Section 1 Section 1 Change over TimeChange over Time

Objectives

• IdentifIdentifyy two kinds of two kinds of evidence that show that evidence that show that organisms have changed organisms have changed over time.over time.

• A characteristic that A characteristic that helps an organism helps an organism survivesurvive and and reproducereproduce in its in its environment is called environment is called an an adaptation.adaptation.

2 kinds of evidence2 kinds of evidence• Some adaptations are Some adaptations are

phphyysicalsical, such as fur or , such as fur or scales. Other adaptations scales. Other adaptations are are behaviorsbehaviors that help an that help an organism find food, protect organism find food, protect itself, or reproduce.itself, or reproduce.

• Individual organisms that share Individual organisms that share the the samesame characteristics might be characteristics might be members of the same members of the same ssppeciesecies. .

• A A ssppeciesecies is a group of organisms is a group of organisms that can that can matemate with one another to with one another to produce fertile produce fertile offsoffspprinring. g.

• Groups of individuals of the same Groups of individuals of the same ssppeciesecies living in the same p living in the same placelace make up a pmake up a pooppulationulation..

Do Species Change over Time?Do Species Change over Time?

• Since life first appeared, Since life first appeared, many species have many species have dieddied out, and many new out, and many new species have species have appearedappeared..

• Scientists observe that Scientists observe that the the inheritedinherited characteristics in characteristics in populations populations changechange over over time. Scientists think time. Scientists think that as pthat as pooppulationsulations change over time, change over time, newnew species species formform..

Objectives

• ExplainExplain how comparing how comparing organisms can provide organisms can provide evidence that they have evidence that they have ancestors in common.ancestors in common.

Comparing Skeletal Structures• The The structurestructure and and orderorder of bones of bones

of a human arm are similar to of a human arm are similar to those of the those of the frontfront limbs of a cat, limbs of a cat, a dolphin, and a bat. a dolphin, and a bat.

• These These similaritiessimilarities suggest that suggest that cats, dolphins, bats, and humans cats, dolphins, bats, and humans had a common had a common ancestorancestor..

Comparing DNA Molecules

• Scientists also compare Scientists also compare organisms at the organisms at the molecular molecular level. level.

• Species that have more Species that have more DNADNA in in common are more closely common are more closely relatedrelated and have shared a common and have shared a common ancestorancestor more recently. more recently.

• The fact that all existing The fact that all existing species have species have DNADNA supports the theory that supports the theory that allall species species shareshare a a common ancestor.common ancestor.

Section 2Section 2

•How Do Population How Do Population Changes Happen?Changes Happen?

Objective

• DescribeDescribe the four parts the four parts of Charles Darwin’s of Charles Darwin’s process of natural process of natural selection.selection.

• NaturalNatural selectionselection is the is the process by which process by which organisms that are better organisms that are better adapted to their adapted to their environment survive and environment survive and reproduce more reproduce more successfully than less well successfully than less well adapted organisms do.adapted organisms do.

Darwin’s Theory of Natural Darwin’s Theory of Natural SelectionSelection

• In 1859, In 1859, DarwinDarwin published a published a famous book called famous book called On the Origin On the Origin of Species by Means of Natural of Species by Means of Natural SelectionSelection. In his book, Darwin . In his book, Darwin proposedproposed the theory that change the theory that change in pin pooppulationsulations happens through happens through natural selection.natural selection.

• Section 3 Section 3 Natural Selection in Natural Selection in

ActionAction

ObjectivesObjectives

• Give two examples of Give two examples of how natural selection can how natural selection can result in an adaptation result in an adaptation that helps an organism that helps an organism survive.survive.

Changes in Populations

• The theory of natural The theory of natural selection selection exexpplainslains how a how a population changes in population changes in resrespponseonse to its environment. to its environment. Well-adaWell-adapptedted individuals will individuals will likely survive and reproduce.likely survive and reproduce.

• Examples:Scientists think that Examples:Scientists think that hunting in Uganda is affecting hunting in Uganda is affecting elephant population. Because ivory elephant population. Because ivory is very valuable, elephants are is very valuable, elephants are hunted for their tusks. So, fewer hunted for their tusks. So, fewer tusked elephants survive to tusked elephants survive to reproduce, and more tuskless reproduce, and more tuskless elephants survive. Tuskless elephants survive. Tuskless elephants pass the tuskless trait to elephants pass the tuskless trait to their offspring.their offspring.

• Examples:An insecticide Examples:An insecticide kills all but a few insects in kills all but a few insects in a population. The a population. The survivors have a gene that survivors have a gene that makes them immune. They makes them immune. They pass it to their offspring pass it to their offspring and after a few generations, and after a few generations, the population is mostly all the population is mostly all immune.immune.

Forming a New SpeciesForming a New Species• Sometimes, Sometimes, drasticdrastic changes that changes that

can form a can form a newnew species takes species takes place. A new species may form place. A new species may form after a group becomes after a group becomes sesepparatedarated from the original population. The from the original population. The formationformation of a new species as a of a new species as a result of change over time is result of change over time is called called ssppeciation.eciation.

ObjectivesObjectives

• Outline the process of Outline the process of speciation.speciation.

• Speciation often begins when a part Speciation often begins when a part of a population becomes of a population becomes sesepparatedarated from the rest. Populations constantly from the rest. Populations constantly undergo undergo naturalnatural selectionselection. After two . After two groups have separated, natural groups have separated, natural selection continues to act on the selection continues to act on the groups. If the groups. If the environmentalenvironmental conditions for each group differ, the conditions for each group differ, the groups’ adaptations will groups’ adaptations will differdiffer..

• Over generations, Over generations, twotwo separated separated groups of a population may become groups of a population may become very very differentdifferent through natural through natural selection due to the selection due to the divisiondivision. Even if . Even if a geological a geological barrierbarrier is removed and is removed and the groups are the groups are reunitedreunited, they may no , they may no longer be able to longer be able to interbreedinterbreed. If they . If they cannotcannot interbreed, the two groups interbreed, the two groups are no longer the are no longer the samesame species. species.