Evolution & Changes Over Time

UNIT UNIT 33

Changes over time, also known as evolution is a process by which modern organisms have descended from ancient organisms.

Evidence of Evolution

1.1. Fossil recordFossil record

2.2. Geographical distributionGeographical distribution

3.3. Homologous structures of living Homologous structures of living thingsthings

4.4. Similarities in early developmentSimilarities in early development

• In 1831, Charles Darwin sailed In 1831, Charles Darwin sailed on the HMS Beagle to observe, on the HMS Beagle to observe, document and collect document and collect specimens around the world.specimens around the world.

• Finches were studied for Finches were studied for adaptations in the Galapagos adaptations in the Galapagos islands.islands.

Darwin’s Voyage

Darwin’s Finches

• On this trip, the data derived On this trip, the data derived helped to form Darwin’s Theory of helped to form Darwin’s Theory of Evolution.Evolution.

• The central ideas of this theory The central ideas of this theory include:include:

a)a) Life changes over timeLife changes over time

b)b) Biological diversity of a species Biological diversity of a species leads to “survival of the fittest”leads to “survival of the fittest”

• Life changes over timeLife changes over time – individual – individual organisms differ and some of this organisms differ and some of this variation is heritablevariation is heritable

• Survival of the FittestSurvival of the Fittest – is the idea – is the idea that in the struggle for existence, the that in the struggle for existence, the use of strength, adaptation, survival use of strength, adaptation, survival and reproduction occur over timeand reproduction occur over time

• Natural SelectionNatural Selection – Darwin’s – Darwin’s Theory is that the struggle for Theory is that the struggle for existence and the survival of the existence and the survival of the fittest take place without human fittest take place without human control or direction. Also, changes control or direction. Also, changes in inherited characteristics occur in inherited characteristics occur over many generations.over many generations.

• Successful Adaptations – enable Successful Adaptations – enable organisms to become better organisms to become better suited to survive and reproduce. suited to survive and reproduce.

–Ex. Quills, better Ex. Quills, better photosynthesis, speed, photosynthesis, speed, camouflagecamouflage

• Species today are descended Species today are descended with modifications from with modifications from ancestral species that lived in ancestral species that lived in the distant past. Diverse the distant past. Diverse species evolve from common species evolve from common ancestors.ancestors.

• In 1795, James Hutton hypothesized that In 1795, James Hutton hypothesized that forces shaped the Earth. Rock layers forces shaped the Earth. Rock layers form slowly over millions of years by form slowly over millions of years by some layers being pushed up by forces, some layers being pushed up by forces, buried or forming mountains.buried or forming mountains.

• Charles Lyell’s theory states that past Charles Lyell’s theory states that past events in terms of processes that are events in terms of processes that are observed which happened millions of observed which happened millions of years ago are still happening today.years ago are still happening today.

• ““The present is the key to The present is the key to the past” is known as the past” is known as uniformatarianism.uniformatarianism.

• The theory that organisms The theory that organisms acquired or lost certain traits acquired or lost certain traits during their lifetime because of during their lifetime because of selective use or disuse of organs selective use or disuse of organs and then passed these traits on and then passed these traits on to offspring was developed by to offspring was developed by Jean-Baptiste Lamarck.Jean-Baptiste Lamarck.

a.a. Vestigal structures – animal organs that Vestigal structures – animal organs that have been reduced in size so that they have been reduced in size so that they are vestiges or traces in other species. are vestiges or traces in other species. They serve no useful function in an They serve no useful function in an organism. (ex: Coccyx bone & organism. (ex: Coccyx bone & appendix in humans)appendix in humans)

b.b. Homologous structures – structures with Homologous structures – structures with different forms in different organisms, different forms in different organisms, but develop from the same embryonic but develop from the same embryonic tissue (ex Bird wings & human arms)tissue (ex Bird wings & human arms)

• In adaptive radiation, fossils indicate In adaptive radiation, fossils indicate that a single species or small group of that a single species or small group of species evolved through natural species evolved through natural selection into diverse forms that live in selection into diverse forms that live in different ways.different ways.

• An adaptation is any inherited An adaptation is any inherited characteristics, physical or behavioral, characteristics, physical or behavioral, that increases an organism’s chance of that increases an organism’s chance of survival.survival.

Giant Tortoises ofthe Galapagos

Islands

• Populations share the same species. Populations share the same species. New individuals and gene New individuals and gene mutations bring alleles into the mutations bring alleles into the population. All genotypes in the population. All genotypes in the population must have equal population must have equal probabilities of survival and probabilities of survival and reproduction. All phenotypes must reproduction. All phenotypes must have any selective advantage over have any selective advantage over another.another.

• In small populations, individuals In small populations, individuals that carry a particular allele may that carry a particular allele may leave more descendants than other leave more descendants than other individuals simply by chance. This individuals simply by chance. This is known as is known as genetic driftgenetic drift..

• Formation of a new species Formation of a new species through natural selection and through natural selection and chance events change alleles chance events change alleles frequency and is referred to as frequency and is referred to as speciationspeciation..

Directional Selection• Individuals at one end of the curve have Individuals at one end of the curve have

higher fitness than individuals in the middle higher fitness than individuals in the middle or at the other end.or at the other end.

• The phenotype of one fails to succeed and The phenotype of one fails to succeed and others do not. The entire curve movesothers do not. The entire curve moves

• Ex: Darwin’s finches with bigger thicker Ex: Darwin’s finches with bigger thicker beaks feed more easily on larger, harder, beaks feed more easily on larger, harder, thicker-shelled seeds (food shortages) text thicker-shelled seeds (food shortages) text p. 398p. 398

Directional Selection

Stabilizing Selection• When individuals near the center of the When individuals near the center of the

curve have the higher fitness than the curve have the higher fitness than the individuals at either end of the curveindividuals at either end of the curve

• Keeps the curve at its current positionKeeps the curve at its current position

• Ex: average babies have the best Ex: average babies have the best survival and best fitnesssurvival and best fitness

Stabilizing Selection

Disruptive Selection

• Upper and lower ends of the curve Upper and lower ends of the curve have higher fitness than individuals have higher fitness than individuals near the middle. The curve splits near the middle. The curve splits into two.into two.

• Ex: Large and small seeds become Ex: Large and small seeds become more common. Text p. 399more common. Text p. 399

Disruptive Selection

• Fossil record – evidence about Fossil record – evidence about the history of life on Earth, how the history of life on Earth, how it has changed over time, and in it has changed over time, and in a particular order.a particular order.

• Sedimentary rocks – rocks Sedimentary rocks – rocks produced by layering of sand, produced by layering of sand, silt, or clay over time.silt, or clay over time.

• Law of superposition – states Law of superposition – states that in undisturbed sedimentary that in undisturbed sedimentary rock layers, the oldest layers are rock layers, the oldest layers are at the bottom and the youngest at the bottom and the youngest are toward the top.are toward the top.