Evolution

What is evolution? Evolution is the

process of biological change by which species of organisms change over time.

Evolution is a central theme in all fields of biology today.

Evolution is when organisms change over time. So, modern organisms

descended from ancient ones.

Evolution is a Theory – Just like Gravity!

• Evolution is a well supported explanation of phenomena that have occurred in the natural world

• A theory in science is a well tested hypothesis, not just a guess

Evolutionary Scientists Charles Bonnet mid-1700s

First to use term evolution Studied fossils

James Hutton 1795 Theory of Geological change

Jean-Baptiste Lamarck 1809 Charles Lyell

Geographical features can be built up or torn down

Charles Darwin Thomas Malthus Russell Wallace

Gave Darwin the drive to publish his findings

Malthus

Reasoned that if the human population continued to grow unchecked, sooner or later there would be insufficient living space and food for everyone

Jean-Baptiste Lamarck He proposed the idea of inheritance of

acquired characteristics: changes in an environment caused an

organism’s behavior to change this would lead to greater use or disuse of a

structure or organ. the structure would become larger or smaller

and would then be passed down to offspring For example: giraffes’ long necks

Idea was WRONG!!

Charles Darwin Natural selection was the

theory he proposed to explain evolution. He attempted to provide

reasons for the biological diversity on Earth.

Developed his theory from personal observations and research of other scientists.

Charles Darwin (1809-1882) Sailed around the world 1831-1836on the British ship H.M.S. Beagle.

What did Darwin’s Travels

Reveal? The diversity of living

species was far greater than anyone had previously known!!

These observations led him to develop the theory of evolution!!

He observed the land and its inhabitants. Finches and Tortoises

What did Darwin do? He noticed the physical differences among

island species. Species on one island looked different from

those on another island. Island species looked different from those

found on the mainland. This is known as variation. Genetic variations arise from mutations

He noticed that the physical differences among the species were appropriate for their environment and diet.

Darwin finally published his ideas in 1859.

Other naturalists were developing the same theory that Darwin did.

Even though he was afraid of the Church’s reaction to his book he wanted to get credit for his work.

Natural Selection

The traits that help an organism survive in a particular environment are “selected” in natural selection

Evidence of Evolution

1. Fossil Record

2. Homologous Body structures

3. Similarities in Embryology

4. Biochemical Evidence

Evidence of Evolution:The Fossil Record

Fossil record provides evidence that living things have evolved

Fossils show the history of life on earth and how different groups of organisms have changed over time

Relative vs. Absolute Dating

Relative Dating

Can determine a fossil’s relative age

Performed by estimating fossil age compared with that of other fossils

Drawbacks – provides no info about age in years

Absolute Dating

Can determine the absolute age in numbers

Is performed by radioactive dating – based on the amount of remaining radioactive isotopes remain

Drawbacks - part of the fossil is destroyed during the test

– A half-life is the amount of time it takes for half of the isotope to decay.

• Radiometric dating uses decay of unstable isotopes.

– Isotopes are atoms of an element that differ in their number of neutrons.

Primate Fossils

Australopithecus Homo erectus Homo sapien

Primate Bone Structure

Evidence of Evolution:Homologous Body

Structures Structures that

have different mature forms but develop from the same embryonic tissues

Ex: Wing of bat, human arm, leg of turtle

Turtle

Alligator

Bird

Evidence of Evolution:Homologous Structures Features that are similar in structure but

appear in different organisms and have different functions.

Strong evidence for common ancestor. Ex: forelimbs of humans, bats and moles.

Human hand Bat wingMole foot

Analogous Structures Structures that perform a similar

function.• Not evidence of common

ancestry.

Vestigial Structures

Remnants of organs or structures that had a function in an early ancestor.

Ex: Ostrich wings, used for balance but not flight

Ex: Humans’ appendix

Evidence of Evolution:Similarities in Embryology

In their early stages of development,

chickens, turtles and rats look similar,

providing evidence that they shared a common ancestry.

Embryological Development

Evidence of Evolution:Biochemical Similarities Scientists study nucleotide sequences in

DNA and proteins in different organisms to determine ancestry.

If the organisms are closely related they will have similar sequences of nucleotides in their DNA and arrangement of amino acids in proteins.

Evidence of Evolution:Biochemical Similarities

Organism Amino Acid Differences

Organism Amino Acid Differences

Human beta chain

0 Mouse 27

Gorilla 1 Kangaroo 38

Rhesus monkey 8 Chicken 45

Dog 15 Frog 67

Cow 25 Soy bean 124

The more similar the

Patterns, Processes, and

Rates of Evolution

Adaptation Darwin’ observations led him to realize

that species must somehow be able to adapt to their surroundings.

Adaptations allow species to better survive in their surroundings.

Adaptations can lead to genetic change in a population over time.

Variation Among Species…

Organisms in the same species have different traits… Known as variation

Variations may result from mutations or from how genetic material is rearranged during sexual reproduction

Variations within a species can have two results:

Speciation Extinction

VariationSpeciation

Individuals with beneficial trait are well suited for the environment They reproduce and pass the beneficial trait to their

offspring

Individuals without the beneficial trait are less likely to survive and reproduce Their traits are not passed.

Beneficial traits are passed while other traits disappear

These changes can eventually cause speciation

Speciation

Evolution of a new species from an existing species

Occurs if the environment changes Individuals with beneficial traits will survive and pass

their traits on to offspring Ex: Colder weather-animal with thicker fur Ex: Type of food-animal equipped to eat new type Ex: New predator-animal able to escape

Speciation Creates Biodiversity Variety of organisms, their genetic information, and

their habitats.

Mechanisms of Evolution Genetic variation that leads to evolution can be a result of

several things:

Mutations Changes in DNA Only mutations in gametes affect evolution

Gene flow Introduction of genes from one population to another Low gene flow=evolution of different species

Gene pool Combination of genetic material from all members of a

population Affected by mobility-more mobility=higher rate of gene flow

Rates of Evolution Catastrophism-

Georges Cuvier He believed that a natural

disaster would occur, cause landforms to change and cause species to become extinct

Once that species went extinct another would come in and take its place

Did not believe species changed over time

Rates of Evolution Two main views:

Gradualism-James Hutton Evolution occurs slowly and constantly over a long

period of time Darwin

Punctuated Equilibrium Evolution occurs in spurts Period of rapid speciation then long period of little to

no change Caused by random mutations or sudden changes in

environment

Cambrian explosion

Rates of Evolution

Uniformitarianism-Charles Lyell Expansion of gradualism Favored theory of geologic change Proposed that changes occur slowly at a constant

rate continuously

VariationExtinction

Permanent loss of a species. Two causes:

Populations fail to adapt Sudden, drastic changes in the environment

Humans attempt to prevent extinction of species through captive breeding, restricting hunting, and creating sanctuaries.

Mass Extinction

Extinction of huge numbers of species in a short period of time

Earth has experienced several mass extinctions 250 million yrs. ago-ocean invertebrates 65 million yrs. ago-dinosaurs