1. Unit B: Life Over Time Chapter 6: Evolution of Living Things
6.1 Earth has been home to living things for about 3.8 billion years
6.2 Species change over time
6.3 Environmental changes can affect populations
6.4 Many types of evidence support evolution

2. 6.2 Species change over time
Before, you learned:
Fossils are evidence of earlier life
More complex organisms have developed over time
Mass extinctions contributed to the development of Earth’s history
Now, you will learn:
About early ideas and observations on evolution
How Darwin developed his theory of natural selection
How new species arise from older species

3. Scientists explore the concept of evolution
Evolution ~ a gradual change over time
“The process through which species change over time”
This change is a result of the change in the genetic material of an organism and is inherited (passed from one generation to the next)

4. Scientists explore the concept of evolution
Early Ideas
Early 1700s: scientists could see species change over time…but how
Jean-Baptiste de Lamarck:
French, early 1800s
proposed that species have changed over time
Based on the idea an individual organism can acquire a new trait during a lifetime and pass it down
Ex: giraffes stretched their necks to reach leaves, passing this trait for long necks to their offspring
What is missing here?
Evidence!

5. Scientists explore the concept of evolution
Darwin’s Observations ( )
Spent 5 years on board the Beagle: sailed from England, along the coast of South America – studied rock formations, fossils, and life
18 Galapagos Islands: plants and animals not only differed from those on the mainland, but also between islands
Alfred Russel Wallace – proposed similar ideas around the same time

6. Darwin’s Observations
Observed several types of tortoises on the islands
Short necks in damp areas with plentiful plant life
Longer necks in dry areas with cacti
Finches, beak shapes and sizes
Heavy, short beaks for pecking trees
Small, thin beaks for capturing insects

7. Natural Selection explains how living things evolve
Darwin struggled to develop an explanation that would account for the diversity he saw
Breeders can produce new variations of an animal over time: artificial selection
New breed: select dogs with a certain trait – mate
Resulting litter: again selectively breed…until a new breed is produced
Darwin: Similar process occurring in nature:
Natural Selection – members of a species that are best suited to their environment survive and reproduce at a higher rate than other members of the species
Based on: overproduction, variation, adaptation, and selection
* both artificial and natural selection have similar results: desired results are passed from one generation to the next…they differ in that humans control one process and the other is due to natural processes
*Theory: a well-tested explanation based on a broad range of facts and observations – not proven, but are generally accepted to be true

8. Natural Selection explains how living things evolve
Population: group of individuals of the same species that live in a particular environment or area
Overproduction:
A plant or animal that reproduces usually makes more offspring than can possibly survive (than the environment can support):
Ex: several thousand salmon eggs, not all hatch, a few hundred survive disease or predation, several dozen reach adulthood, and few will successfully reproduce
Variation
Species have natural differences/variations in traits – ex: fin size
These are passed on from one generation to the next
Genetic material may change – new variation (mutation)
Reproduction: passes these traits to offspring
Adaptation
A mutation can make an individual better able to survive
An advantage in the particular environment; ex: tail shape – swim faster
Selection
Particular adaptations lead to survival long enough to reproduce
That adaptation becomes more common in the next generation of offspring
Genetic variation: differences in DNA in a population
Environmental factors: conditions that affect survival – include food supply, habitat, predators, and disease

13. Darwin’s Theory of Evolution by Natural Selection
basic idea – “Descent with modification”
Although some details were absent (or under-developed because he couldn’t know, for example, the structure of DNA and the mechanism of inheritance), Darwin’s fundamental ideas have been supported by overwhelming evidence from morphological, biochemical, fossil, behavioral, and direct observational data

14. New species develop from earlier species
In 1859, after more than 20 years of work, Darwin published, On the Origin of Species
Speciation:
Evolution of new species from an existing species
Environmental changes (rapid or gradual)
Ex: in book Lake Tanganyika: over 150 cichlid species pB24
Isolation:
Darwin’s trip to the Galapagos: islands were separated from the mainland by miles of ocean, ad unable to breed with mainland relatives
New species evolved
Darwin: isolation of population by geographical or other barriers could contribute to the process of speciation
Today: isolation is essential to speciation – for species to separate, two populations must be prevented from reproducing with each other
Geographic boundary – ocean, mountain range, feed on different things, reproduce at different times of the year
Mutations in one isolated group may differ from another…two populations may evolve differently from each other  Speciation  BIODIVERSITY on Earth