Lesson 2 Evidence for Evolution

Question 1

Evidence for Evolution

Answer 1

There is a significant amount of evidence that evolution is occurring and has occurred in the past. We will look at:

Age of the Earth

Fossils

Similarities in early development

Patterns of variation

Similarities in body structures

Artificial selection

DNA Comparison

Question 2

Age of the Earth

Answer 2

The planet Earth is more than 4 billion years old

This was postulated by two geologists in Darwin’s time

James Hutton (1788)

Proposed that rocks, mountains and valleys had been changed gradually by rain, heat and cold, the activity of volcanoes and other natural forces

Charles Lyell (1830)

Agreed with Hutton and suggested that the land is constantly moving and shifting. Forces beneath the Earth’s surface twist and bend some rock layers, bury others, and even push up some parts of the sea floor into mountain
ranges.

Question 3

Fossils

Answer 3

Preserved remains of ancient organisms found in rock,
sediment and stone

Many fossils found by geologists in the 1800’s did not resemble any currently living creatures

The fossil record represents the preserved collective history of the Earth’s organisms but it is incomplete.

Question 4

Fossil Dating
Techniques

Answer 4

Relative Dating

A technique used by scientists to
determine the age of fossils relative
to other fossils in different layers of
rock
Limited because geologists did not know how long it took each layer to form

Question 5

The Geological Time
Scale

Answer 5

Scientists noticed that certain
layers of rock appeared in the
same vertical order wherever
they were found

Lower layers were formed first
and were older than upper layers

Assuming that the ground has
not been disturbed, scientists
could determine the
approximate dates of the fossils

Question 6

Fossil Dating
Techniques

Answer 6

2. Radioactive Dating

-Rock contains radioactive elements
that decay over time

-The traces of radioactive isotopes
present in a sample allow geologists to determine the approximate age of the sample.

Geologists use a unit called the “half life” to determine the age of the sample.

-A “half – life” is the time it takes for ½
of the atoms of a radioactive element
to decay.

Question 7

Carbon-14
Dating

Answer 7

A useful form of radioactive dating
that is used to measure the age of
material that was once alive (like
bones)

Carbon-14 is present in the
atmosphere and is absorbed by living
bodies

After an organism dies it can no
longer absorb carbon – 14 and it
decays into nitrogen - 14.

By comparing the amount of Carbon –
14 and Nitrogen – 14, scientists can
determine the age of a sample.

Not accurate for samples more than
60000 years old.

Question 8

Two Problems with Fossil
Evidence

Answer 8

Fossils left behind represent some of the organisms from the past BUT only those in areas with sedimentary rock formation
Not all organisms are preserved well as fossils

Question 9

Similarities in Early Development

Answer 9

Many embryos are
similar in appearance
during the early stages
of development

Question 10

Patterns of Variation

Answer 10

Since populations change
over time, at any one
moment we should be
able to see examples of
different stages of this
change.

This is evident in many
populations including the
Finches observed by
Darwin.

Common example used
to demonstrate this is the
peppered moth.

Question 11

Similarities in Body
Structures 1

Answer 11

Basic morphology (body shape) appears to be similar in a variety of different species

Homologous Structures:

Dissimilar parts of different organisms that developed from the same ancestral body part

Ex. Human arm and fish fin

Analogous Structures:

Structures that are similar in appearance and function BUT have different origins and usually
different internal structures

Ex. Bird wing and insect wing

Vestigial Structures:

Structures that no longer serve a useful purpose or
function in an organism

Ex. Small pelvis and thigh bone found in the
body of whales and some snakes.

Question 12

Artificial Selection

Answer 12

Selective breeding of domesticated animals shows that selection can cause evolution.
Humans have deliberately bred certain animals for thousands of years. The modern breeds of domesticated animals show huge differences from the wild species they most resemble.

Considerable changes have occurs as a result of humans selectively breeding the domestic animals for desirable characteristics.

This shows that selection can cause evolution but does not prove that evolution has occurred naturally or that natural selection is the mechanism for evolution.

Question 13

DNA
Comparison

Answer 13

Comparison of DNA or RNA gives an
indication of how closely “related” two
organisms are and how recently they split
from the same evolutionary path.