Chapter 6

 The fossil record is made up of all the fossils ever discovered on Earth.
 The fossil record provides evidence that species have changed over time.
 Based on fossil evidence, scientists can recreate the physical appearance of species that are no longer alive on Earth.

 Usually only the hard parts of an animal remain such as bones, teeth or shells
 In plants, leaves, stems, roots, or seeds can leave behind fossils.
 Fossils rarely occur, and most form when an organism dies and becomes buried in sediment.

 The impression of an organism found in a rock is called a mold
 A cast is a fossil copy of an organism in a rock

Trace Fossils - the preserved evidence of the activity of an organism.
 Evidence that life has changed over time
 Oldest fossils are very simple

 Instead of dating fossils directly, scientists date the rocks the fossils are embedded inside.
 If the age of the igneous layers is known, it is possible to estimate the age of the sedimentary layers —and the fossils they contain —between them.
 Deeper fossils look less like present day organisms

 The geologic time scale is a chart that divides Earth’s history into different time units.

 Extinction occurs when the last individual organism of a species dies.
 A mass extinction occurs when many species become extinct within a few million years or less.
 Extinctions can occur when environments change and organisms can’t adapt quickly enough

 The fossil record contains evidence that five mass extinction events have occurred during the Phanerozoic eon.

 The fossil record contains evidence of the appearance of many new species over time.
 Biological evolution is the change over time in populations of related organisms

 The fossil record shows evidence that horses descended from organisms for which only fossils exist today.

In December 1831, the British naval ship
HMS Beagle set sail in England for a 5 year long trip around the world.

•Charles Darwin, a British
Naturalist was on board.
• A naturalist is a person who studies plants and animals by observing them.
• His job was to learn as much as he could about the living things he saw on the voyage,

 During the voyage, he observed many plants and animals that he had never seen before
 He wondered why there were so different than the plants and animals in England.
 What do you think?
 This led him to his theory of Evolution by
Natural Selection.

In 1835, the Beagle reached the
Galapagos Islands
- a group of small islands in the Pacific
Ocean off the west coast of South
America

 Darwin studied many animals on the islands
& noticed differences & similarities between them
 For example, the tortoises on one island had dome shaped shells and on another island had saddle-shaped shells.
 The finches on each island had different size and shaped beaks.
 Why?
 They had to adapt to their environment.

Darwin found that each island in the
Galápagos had a different environment, and tortoises looked different depending on which island environment they inhabited.

 The Iguanas on the Islands had large claws and the Iguanas on the mainland had smaller claws.
 Why?
 Large claws allowed the Iguanas to hold on to the slippery rocks to feed on seaweed.
 Small claws allowed the Iguanas to climb trees where they ate leaves.

Marine Iguana
Mainland Iguana

 Cormorants (large sea birds) were able to fly on the mainland but could not fly on the Islands.
Flightless Cormorant
Mainland Cormorant

 Darwin observed that many of the species on the Galapagos Islands were similar to those on the mainland.
 Why?
 Where did they come from?

 Darwin inferred that some of the animals from mainland Ecuador came over to the Islands
 They might have been blown out to sea during a storm or drifted on a log millions of years ago

 Finches on the Galapagos Islands differed slightly from the finches in
Ecuador too
 The finches on each of the Galapagos
Islands were also different from each other
 Mainly the shape of their beaks and the food they ate were different depending what was available on their island
 The finches had to adapt to life on their island or perish

Darwin’s Finches of the Galapagos

 Darwin realized the Galapagos animals came from common ancestors, but had changed over time & now had slight differences or variations.
– A variation is a slight difference in an inherited trait of individual members of a species.
 Variations arise naturally in populations, occurring in offspring as a result of sexual reproduction.
– The #1 source of variations are genetic mutations, which are changes in a gene
 Genetic changes to phenotype can be passed on to future generations.

 Darwin believed these variations occurred through the process of Natural Selection
 Natural Selection is the process by which organisms with favorable variations that help them survive in their environments live longer, compete better, and reproduce more than those that do not have the variations.
 Natural selection explains how populations change as their environments change.

 1858 Alfred Russell Wallace proposed a theory of evolution
 1859 Darwin wrote
– The Origin of the Species
– In it, he says that evolution occurs by natural selection
– Individuals that are better adapted to their environment are more likely to survive and reproduce
– “survival of the fittest”

1. Reproduction
 Most species naturally produces more offspring than will survive to maturity
 Starvation, disease, predators affect the size of their population
 Limited number survive to reproduction age
 Offspring of the strongest organisms inherit traits that help them survive in their environment

 Offspring have slightly different traits from one another
 Some traits increase the chances of survival and reproduction, others decrease the chances of survival
 These variations are inherited

 Natural environments do not have enough food, water, and other resources
 Offspring fight for food, water, and other resources
 Some become prey for predators
 Only the fittest (strongest) survive to adulthood

 Offspring that are better adapted to the environment will be naturally
“selected” to survive & reproduce to keep the species going

 1. Reproduction
 Species produces more offspring than will survive
 2. Genetic Variation
 Offspring have different traits
 Some traits increase chances of survival
 3. Competition
 Offspring fight for food, water, and other resources
 Some become prey
 The fittest survive to adulthood
 4. Selection
 Offspring better adapted to environment are more likely to reproduce

 Peppered Moths
 Before 1850, dark peppered moths were rare and pale were more common.

After 1850’s, dark peppered moths became more abundant in heavily industrialized areas.

 Several species of birds eat the peppered moths.
 Pale moths blended into their surroundings and dark moths were eaten more frequently.

 Soot and smoke from industrial areas blackened nearby trees
 Dark moths became less visible and pale moths stood out and became easy prey
 More dark moths survived and produced more dark offspring
 Population changed from mostly light-colored moths to mostly dark-colored moths

 Through natural selection, a helpful variation in one individual can spread to all members of a population.
 An adaptation is an inherited trait that increases an organism’s chance of surviving and reproducing in its environment.
 Adaptations can be structural or behavioral
– Example: structures and behaviors for finding food, for protection, and for moving from place to place

 Arctic hare-
– white fur in winter provides camouflage from predators
• (structural adaptation)

 Monkey-
– Grasping tail acts as an extra hand to aid movement through trees
• (structural adaptation)

 Cactus
– Waxy skin reduces water loss from evaporation
• (structural adaptation)

 Black Bear
– Hibernates to adapt to seasonal changes
• (behavioral adaptation)

Artificial Selection
 The breeding of organisms for desired characteristics is called selective breeding
 Darwin realized that changes caused by selective breeding were much like changes caused by natural selection, but done by humans.
 Humans can choose to breed individuals with desired traits
– Farmers can choose to breed only corn with plump corn kernels
– Dog breeders choose which dogs to breed by selecting traits

 A species is a group of similar organisms that can mate with each other and produce fertile offspring.
 Species evolve so they can survive in their changing environment.
 Not all members of a species are strong enough to evolve and survive.

 Isolation or complete separation occurs
 Over time new traits are developed
 Formation of a new species can happen in 3 steps:

 A portion of a population becomes isolated from the rest of the population by:
– newly formed canyon, mountain range, lake

 If the population is divided, the environment may also change and so may the population that lives there
 The separated groups may adapt to better fit their environments

 2 groups may become so different that they can no longer interbreed
 They are no longer the same species

1.
2.
3.
4.
5.
6.
Darwin’s Finches may have evolved this way:
Some finches left the mainland and reached one of the islands (separation)
The finches reproduced and adapted to the environment (adaptation)
Some finches flew to a second island (separation)
The finches reproduced and adapted to a different environment (adaptation)
Some finches flew back to the first island but could no longer interbreed with those finches (division)
This process may have occurred over and over again as the finches flew to the other islands




1.Separation
– Portion of a population becomes isolated from the rest of the population by:
• Newly formed canyon
• Mountain range
• Lake
2.Adaptation
– As environment changes, separated groups adapt to their new environment
3.Division
– Groups of a population become so different they can no longer interbreed
• Different species form

 Evolution is the process by which populations accumulate inherited changes over time
– Because of evolution, scientists think that all living things share a common ancestor

Evidence for common ancestry
Homologous structures
 Homologous structures are body parts of organisms that are similar in structure and position but different in function.
 Suggests a common ancestor

Evidence for common ancestry
 Body parts that perform a similar function but differ in structure are analogous structures

Evidence for common ancestry
 Vestigial Structures are body parts that have lost their original function through evolution.
Remnants of hind-limb bones are embedded inside the whale’s body

“
Leftovers”
 Examples:
– Human Tail Bone
– Appendix
– Tonsils
– Wisdom teeth

Comparing DNA
 Looking at similarities in DNA
 Human and chimpanzee DNA 99% identical
 Suggests common ancestor

 Turtle
 Chicken
 Rat

Turtle Chicken Rat

 All have a tail
 All have gill slits
 They share a common ancestor

 Similar appearance early in embryonic development
 The science of the development of embryos from fertilization to birth is called embryology
 Suggest common ancestor