CHAPTER 15

Darwin’s Theory of Evolution

15.1 The Puzzle of Life’s Diversity

Evolution: Change over time, is the process by which modern organisms have descended from ancient organisms.

Scientific Theory: A well supported testable explanation of phenomena that have occurred in the Natural World.

Voyage of the Beagle

Charles Darwin was born in Shrewsbury, England on February 12, 1809

Joined the crew of the H.M.S. Beagle

He set sail in 1831 and his voyage took 5 years!

Voyage of the Beagle

During his travels: Darwin made numerous observations and collected evidence

This led him to propose a revolutionary hypothesis about the way life changes over time

NorthAmerica

Europe

GreatBritain

Africa

Equator

Asia

Australia

TasmaniaNewZealand

PACIFICOCEAN

ATLANTICOCEANPACIFIC

OCEAN

PACIFICOCEAN

TheGalápagosIslands

SouthAmerica

Tierra del Fuego

Cape Horn

Cape ofGood HopeA

ndes

Pinta

MarchenaGenovesa

EquatorSantiago

Isabela

Fernandina

Florenza Española

SanCristobal

SantaCruz

SantaFe

Pinzón

DaphneIslands

40 miles

40 km0

0

Darwin’s Observations

In Brazil, Darwin collected 68 different beetle species.

Patterns of Diversity: Why did some animals grow in some areas and not in others?

Why did the same species of animal look different from one another depending on where they lived?

Living organisms and Fossils: Preserved remains of Ancient organisms.

Darwin’s Observations

The Galápagos Islands: The tortoises varied from Island to Island depending on the vegetation.

He also noticed that the birds on each of the islands had different sizes and beak sizes.

The Tortoises!

http://www.skeptic.com/eskeptic/06-07-28images/TortoiseonPinzon.jpg

http://imagecache01a.allposters.com/images/pic/PTGPOD/OSJOM-00000498-001-FB~Espanola-Saddleback-Tortoise-Adult-Female-Galapagos-Posters.jpg

The Journey Home

Darwin observed that the characteristics of many animals and plants varied noticeably among the different islands of the Galápagos

The Tortoises!

http://research.unc.edu/internal/galapagos/santa_cruz/turtles_feeding.jpg

http://mysite.du.edu/~ttyler/ploughboy/cht102.jpg

15.2 Ideas That Shaped Darwin’s Thinking

We need to learn something about the time and world that Darwin lived in.

Most Europeans believed that the Earth and everything in it was created only a few thousand years ago.

Therefore, all creatures were the same from when they were first created.

Ideas That Shaped Darwin’s Thinking

During the 1800’s explorers were finding many fossil remains of numerous animal types that had no living representatives. This challenged the traditional view point of the time.

After a lot of studying Darwin changed his thinking dramatically.

An Ancient Changing Earth

Hutton and Geological Change In 1795, Hutton published his hypothesis about Geological forces that have shaped the Earth.

He proposed that rock layers form very slowly by up pushed earth or by rock layers forming on top of others

This meant and he proposed the earth was much more than a few thousand years old.

An Ancient Changing Earth

Lyell’s Principles of Geology His first book Principles of Geology He stressed that scientists must explain past events in terms of processes that they can actually observe, since processes that shaped the Earth millions of years earlier.

Erosion continues to carve out canyons, just as it did in the past

Lyell helped Darwin appreciate the significance of geological phenomena that he observed.

The Understanding of Geology Influenced Darwin in 2 Ways

1. If Earth could change over time, might life change as well?

2. He realized that it would have taken a very long time for life to change in the way he suggested.

15.3 Darwin Presents His Case

Publication of On the Origin of Species In 1858, Darwin received a short essay by Alfred Russel Wallace.

Wallace’s paper talked about his thoughts on evolutionary change that Darwin had been mulling over for 25 years!

Evolution by Natural Selection

Nature selects for those traits that will help a species survive.

For example: Certain colors, beak strength, etc.

The Struggle for Existence

Members of each species complete regularly to obtain: Food Living space Other necessities of life

Survival of the Fittest

Darwin observed how well suited an organism is to its environment

Fitness: Ability of an individual to survive and reproduce in its specific environment

Adaptation: Any inherited characteristic that increases an organism’s changes of survival.

Survival of the Fittest

Successful adaptations allow an organism to be better suited to their environment thus increasing their rate of survival and ability to reproduce

Natural Selection

Over time, natural selection results in changes in the inherited characteristics of a population. These changes increase a species’ fitness in its environment.

Descent with Modification

After long periods of time, natural selection produces organisms that have different structures, establish different niches or occupy different habitats. As a result species look different from their ancestors.

Common Descent: According to this principle, all species, living and extinct were derived from common ancestors

Hundreds to thousandsof years of breeding(artificial selection)

Ancestral dog (wolf)

Thousands tomillions of years

of natural selection

Ancestral canine

African wild dog

Coyote

Wolf Fox Jackal

A flower mantidin Malaysia

A leaf mantid in Costa Rica

Evidence of Evolution

Darwin argued that living things have been evolving on Earth for millions of years.

Evidence for this process could be found in: The fossil record The geological distribution of living species

Homologous structures of living organisms Similarities in early development or embryology

The Fossil Record

By comparing fossils from older rock layers with fossils from younger layers.

Scientists can now document the fact that life on Earth has changed over time.

There are gaps in the fossil records but each time a new fossil gets found the gap shrinks.

A Skull of Homoerectus

D Dinosaur tracksC Ammonite castsB Petrified tree

E Fossilized organicmatter of a leaf

G “Ice Man”

F Insect in amber

Geographic Distribution of Living Species

Birds in the Galápagos Islands looked different but where actually finches

They descended from a common ancestor

Animals that live in the same environment, animals will develop similar anatomies and behaviors

Homologous Body Structures

Limbs vary greatly in form and function However they are all constructed from the same basic bones

Homologous Structures: Structures that have different mature forms but develop from the same embryonic tissues

Vestigial Organs: Organs that serves no useful function in an organism

Similarities in Embryology

In early stages, or embryos, with backbones are very similar

Due to the fact that the same groups of embryonic cells develop in the same order and in similar patterns to produce the tissues and organs of all vertebrates.