Evolution: Grade 12

Introduction

Distinguish between a hypothesis and a theory

• Hipothesis consists of the following key concepts

– Dependent variable– Independent variable– relationship between the two variables– Testable

Summary: An educated statement/ guess (two variables) which is testable

NOT A QUESTION

During an investigation which is testing your hypothesis, the findings or results, might end in one of the following:

Your hypothesis is ...1. not rejected / accepted

2. rejected, or

3. adapted (create new or more questions)

NOT PROVEN

Constructing new scientific knowledge

A number of not rejected, interrelated hypotheses, which provide usually complex inferences and explanations …

construct new scientific knowledge

Leads to theories

Distinguish between a hypothesis and a theory

Theory consists of the following key concepts– Overarching explanations of interrelated

hypotheses that have been tested and not rejected/accepted

– These well-substantiated explanations incorporate facts, laws, inferences, and tested hypotheses

– Allow scientists to make valid predictions/ conclusions.

A theory deals mainly …

• of how aspects (processes and/or mechanisms in life)

• in the natural world work.

Some basic definitions

• Fact: an observation that has been repeatedly confirmed / verified over years

• Law: a descriptive generalization about how the physical world behaves under certain conditions

• Hypothesis: a testable statement that can be used to build inferences and explanations

EVOLUTION: Content

• History

• Definition

• Natural Selection

• Spesiation

• Bewyse vir evolusie– Fossil records - Transitional stage– Modification from ancestor – Biogeography– Genetics

History of the earlier development of the evolution theory

Four persons have played an important role in the development of the earlier evolution theory, namely,

1. Erasmus Darwin’s ideas (1731-1802 Grand father of Charles):

• All life developed from simple forms• There are similarities amongst various

organisms• Artificial selection and metamorphosis showed

how changes may have occurred

History: Lamarck

2. Jean Baptiste de Lamarck (1744–1829) His two ideas:

1. Use and disuse

• Changes in the environment create new needs that cause organisms to modify their existing organs to meet the need. Repeated use of the organ would cause it to enlarge and become more efficient. Disuse of a organ would cause it to degenerate

2. Inheritance of modified characteristics

• The modification an organism acquired during its life time could be pass on to its offspring.

History: Lamarck

Lamarck: Examples

Examples of the application of Lamarck’s ideas

(e.g. Long neck of the giraffe or the legs of a snake)

Misuse

• Legs of snake disappeared because it did not use them in its gliding movement;

• Their bodies became thin and long to allow them to crawl through narrow spaces

• Penguins without wings

• Ducks stretch their toes apart to achieve an efficient swimming stroke and the skin between the toes also became stretched

Lamarck DarwinIndividuals want to adapt to the environment(determinism, internal drive)

No drive to change (no internal drive)

Individuals in population change

Change because of environmental factors

Variation because individual change

Offspring showed variation when produced

Change acquired during life time inherited from parent to offspring

Natural selection – favourablecharacteristics inherited from

parents to offspring

DIFFERENCES

Lamarck: Rejected Reasons for Lamarck’s theory being rejected:1. Theory is deterministic. He imagined that

all organisms had an internal drive to ascend the ladder of development during evolution. He did not think of evolution in a tree-like form.

Lamarck: Rejected (cont) Reasons for Lamarck’s theory being

rejected:2. Inheritance of acquired characteristics

can’t take place. No change to its HERITABLE MATERIAL. No genetic basis for this.

3. Environmental factors only can`t cause evolution – variation must be present as well / natural selection

History: Charles Darwin

3 Charles Darwin (1809-1882)Theory of evolution by natural selection under the

following captions:

• Darwin’s 5-year voyage around the world in the HMS Beagle, collecting specimens and keeping notes of plants, animals seen and geography of countries visited.– The historical development. In 1858 he was aware of Wallace’s

work. Afraid to publish his ideas, because people might think that he has stolen Wallace’s ideas.

– Darwin’s article together with Wallace’s article were presented during the “Linnaean Society conference” at 1 July 1858.

– Publication of “On the Origin of the Species” in 1859

History: Charles Darwin (cont.)The observations on which Darwin based

his theory:

• Organisms of a species produce a large number of offspring

• The offspring show a great deal of variation

• Of the large number of offspring produced, only a few survive

• Characteristics are inherited from surviving parents to offspring

History: Wallace

4 Alfred Wallace (1823-1913)

Wallace and Charles Darwin have independently described natural selection as an explanation for evolution.