Evolution Notes

Unit 6

14.1 Fossil Evidence of Change

Land Environments

The History of LifeChapter 14

Earth formed about 4.6 billion years ago.Pangaea: the supercontinent believed to

have existed 300 million years ago where all of the continents today were one large land mass.

Clues in Rocks

The History of Life

A fossil is any preserved evidence of an organism.

Why are there gaps in the fossil record?

Most organisms decompose before they have a chance to become fossilized.

14.1 Fossil Evidence of Change

Chapter 14

The History of Life

14.1 Fossil Evidence of Change

Chapter 14

Fossil Formation

The History of Life

Nearly all fossils are formed in sedimentary rock.

14.1 Fossil Evidence of Change

Chapter 14

Dating fossils

The History of Life

Relative dating is a method used to determine the age of rocks by comparing them with those in other layers.

14.1 Fossil Evidence of Change

Chapter 14

Uses the decay of radioactive isotopes to measure the age of a rock

Radiometric Dating

The History of Life

• Half-life: amount of time required for half of a radioactive isotope to decay.

14.1 Fossil Evidence of Change

Chapter 14

The geological time scale is a model that expresses the major geological and biological events in Earth’s history.

The Geologic Time Scale

The History of Life

14.1 Fossil Evidence of Change

Chapter 14

Terminology to know!• Hypothesis An “If…then” statement or

proposal of an outcome of an experiment.(Ex. If I study, then I will pass the test.)

• Theory A hypothesis that has withstood extensive testing by a variety of methods, and in which a higher degree of certainty may be placed (Ex. Theory of Evolution)

• Law Considered universal and invariable facts of the physical world (Ex. Law of Gravity)

Cellular Evolution

The History of Life

Scientists hypothesize that the first cells were prokaryotes.

These would compare to our modern day bacteria

14.2 The Origin of Life

Chapter 14

The Endosymbiotic Theory

The History of Life

Eukaryotic cells arose from communities formed by prokaryotic cells.

This theory explains the origin of chloroplasts and mitochondria.

14.2 The Origin of Life

Chapter 14

The History of Life

14.2 The Origin of Life

Chapter 14

The History of Life

The History of Life: Self Check!

Chapter 14

1. How would you explain to someone the way fossils demonstrate evidence of evolution?

2. Describe how relative dating is used to identify similarly aged rocks in different locations.

3. Mitochondria and chloroplasts containing their own circular DNA is evidence that supports what theory?

Fossils are the main evidence of evolution because they show ancestors of modern species. They show that ancient species share similarities with species now on Earth.

How deep the rock layer is where the fossils were found.

Endosymbiot Theory

15.1 Darwin’s Theory of Natural Selection

Darwin on the HMS Beagle

Evolution

His job was to collect biological and geological specimens during the ship’s travel.

Chapter 15

What can explain the large extent of biological diversity on earth?

• Evolution – change over time– How life has changed over time

The Galápagos Islands

Evolution

Darwin began to collect mockingbirds, finches, & other animals on the 4 islands.

He noticed that the different islands seemed to have their own, slightly different varieties of animals.

15.1 Darwin’s Theory of Natural Selection

Chapter 15

The Galapagos Islands

• West of South America• Group of islands each with

different climates• Tortoises varied from island to

island in neck length and shell shape

• Finches varied in beak shape• Characteristics of plants and

animals varied from island to island

Evolution

15.1 Darwin’s Theory of Natural Selection

Chapter 15

Darwin Continued His Studies

Evolution

Darwin inferred that if humans could change species by artificial selection, then perhaps the same process could work in nature.

15.1 Darwin’s Theory of Natural Selection

Chapter 15

Natural Selection

Evolution

Individuals in a population show variations.

Variations can be inherited.

Organisms have more offspring than can survive with available resources.

Variations that increase reproductive success will have a greater chance of being passed on.

15.1 Darwin’s Theory of Natural Selection

Chapter 15

“Survival of the Fittest”

The Origin of Species

Evolution

Darwin published On the Origin of Species by Means of Natural Selection in 1859.

It is a means of explaining how evolution works.

15.1 Darwin’s Theory of Natural Selection

Chapter 15

Lamarck’s Theory• Pre-Darwin scientist• Inheritance of acquired traits• Organs used a lot could grow and change shape• Organs not used would shrivel and disappear• Theory was incorrect but significant because he was the first

scientist to recognize that organisms had changed over time

15.2 Evidence of Evolution

Support for Evolution

Evolution

The fossil record

Glyptodont

Provide a record of species that lived long ago.

Show that ancient species share similarities with species that now live.

Armadillo

Chapter 15

Geographic Distribution

Evolution

The distribution of plants and animals that Darwin saw first suggested evolution to Darwin.

Biogeography: The study of the distribution of plants and animals on Earth.

Rabbit Mara

15.2 Evidence of Evolution

Chapter 15

Support for Evolution

Evolution

Derived traits are newly evolved features, such as feathers, that do not appear in the fossils of common ancestors.

Ancestral traits are more primitive features, such as teeth and tails, that do appear in ancestral forms.

15.2 Evidence of Evolution

Chapter 15

Homologous StructuresAnatomically similar structures inherited

from a common ancestor

Evolution

Same function but different structure

NOT inherited fromcommon ancestor.

Analogous Structures

Chapter 15

Evolution

Vestigial Structures

Structures that are the reduced forms of functional structures in other organisms.

15.2 Evidence of Evolution

Chapter 15

Evolutionary theorypredicts that features of ancestors that no longer have a function for that species will become smaller over time until they are lost.

Evolution

Comparative Morphology: Analysis of the form and structure of multiple species.

Ancestral Characteristics: Morphological or biochemical feature present in various groups within the line of descent.

Organisms with closely related morphological features have more closely related molecular features.

15.2 Evidence of Evolution

Chapter 15

More Terms• Fitness – ability of an individual

to survive and reproduce in a specific environment

• Adaptation – inherited characteristic that increases an organism’s chance of survival–Can be physical traits as well as behavioral traits

Evolution

Camouflage

Allows organisms to become almost invisible to predators

Leafy sea dragon

15.2 Evidence of Evolution

Chapter 15

Evolution

Mimicry

One species evolves to resemble another species.

Western coral snake California kingsnake

15.2 Evidence of Evolution

Chapter 15

Evolution

Natural Selection

Acts to select the individuals that are best adapted for survival and reproduction

15.3 Shaping Evolutionary Theory

Chapter 15

Evolution

Stabilizing selection operates to eliminate extreme expressions of a trait when the average expression leads to higher fitness.

15.3 Shaping Evolutionary Theory

Chapter 15

Ex. Siberian Husky

Evolution

Directional selection makes an organism more fit.

15.3 Shaping Evolutionary Theory

Chapter 15

Favors the extremesEx. Greyhound Dog

Evolution

Disruptive selection is a process that splits a population into two groups.

15.3 Shaping Evolutionary Theory

Chapter 15

Ex. Black, White, & Gray Rabbits

15.3 Shaping Evolutionary Theory

Mechanisms of Evolution

Evolution

Population genetics

Hardy-Weinberg principle states that when allelic frequencies remain constant, a population is in genetic equilibrium.

Chapter 15

Evolution

15.3 Shaping Evolutionary Theory

Chapter 15

Write these down & know these!

Evolution

Genetic Drift A change in the allelic frequencies in a

population that is due to chance and random mating

In smaller populations, the effects of genetic drift become more pronounced, and the chance of losing an allele becomes greater.

Marble Example

15.3 Shaping Evolutionary Theory

Chapter 15

Evolution

Nonrandom Mating

Promotes inbreeding & could lead to a change in allelic proportions favoring individuals that are homozygous for particular traits

15.3 Shaping Evolutionary Theory

Chapter 15

Evolution

Founder Effect

The loss of genetic variation that occurs when a new population is established by a very small number of individuals from a larger population

15.3 Shaping Evolutionary Theory

Chapter 15

Mainland

Island 3

Island 2

Island 1

Evolution

Bottleneck a significant percentage of a population or

species is killed or otherwise prevented from reproducing and can rebound later

15.3 Shaping Evolutionary Theory

Often caused by a natural disaster

What is a gene pool?

• Gene pool – combined genetic info of all members of a population– Contains two of more

alleles (genes) for the same trait

– Allele frequency – number of times an allele occurs in a gene pool compared to the number of times another allele occurs (expressed in percents)

Sample Population

48% heterozygous

black

36% homozygous

brown

16% homozygous

black

Frequency of Alleles

allele for brown fur

allele for black fur

Relative Frequencies of AllelesSection 16-1

Gene Flow• Genes entering or leaving a population

• AKA. Migration– Emigration Genes LEAVING a population– Immigration INCOMING genes in a population

What are sources for genetic variation?

• Mutations – random change in the DNA, may cause evolution in future populations

• Genetic shuffling – occurs in meiosis when gametes are formed

Evolution

Sexual selection operates in populations where males and females differ significantly in appearance.

15.3 Shaping Evolutionary Theory

Chapter 15

Evolution

Prezygotic isolation prevents reproduction by making fertilization unlikely.

Eastern meadowlark and Western meadowlark

15.3 Shaping Evolutionary Theory

Chapter 15

•In behavioral isolation, patterns of courtship may be different.

•In temporal isolation, different groups may not be reproductively mature at the same season, or month, or year.

•In ecological isolation, not in the same habitat where they are likely to meet.

Postzygotic isolation occurs when fertilization has occurred but a hybrid offspring cannot develop or reproduce.

Evolution

Prevents offspring survival or reproduction

Liger

15.3 Shaping Evolutionary Theory

Chapter 15

Evolution

Allopatric Speciation

A physical barrier divides one population into two or more populations.

Abert squirrel Kaibab squirrel

15.3 Shaping Evolutionary Theory

Chapter 15

Evolution

Sympatric Speciation

A species evolves into a new species without a physical barrier.

The ancestor species and the new species live side by side during the speciation process.

15.3 Shaping Evolutionary Theory

Chapter 15

Evolution

Adaptive Radiation

Can occur in a relatively short time when one species

gives rise to many different species in response to the creation of new habitat or some other ecological opportunity

15.3 Shaping Evolutionary Theory

Chapter 15

Evolution

Coevolution

The relationship betweentwo species might be so close that the evolution ofone species affects the evolution of the other species.

Mutualism

Coevolutionary arms race

15.3 Shaping Evolutionary Theory

Chapter 15

Evolution

Unrelated species evolve similar traits even though they live in different parts of the world.

Convergent Evolution

15.3 Shaping Evolutionary Theory

Chapter 15

Evolution

Rate of Speciation

Evolution proceeds in small, gradual steps according to a theory called gradualism.

Punctuated equilibrium explains rapid spurts of genetic change causing species to diverge quickly.

15.3 Shaping Evolutionary Theory

Chapter 15

Evolution

15.3 Shaping Evolutionary Theory

Chapter 15