A complete set of notes on the Evolution section of the IEB Matric / Grade 11 Syllabus for Life Sciences [Biology]. These notes helped me to achieve a distinction for my Life Science Prelim. These notes include an in-depth analysis of both Evolution theories and Human Evolution.
- People have thought about the diversity of living organisms & how they arrived on
earth
- Each culture has a traditional story about origins of different forms of life
- Ideas about the origin of the variety of living organisms can be based on either or:
• Evolution
- Ideas based on evolution are scientific
- Suggest that populations go through a process of evolution that changes with
time
• Creation
- Ideas based on creation are not scientific
- They do not depend on observation & investigation
- Evolution:
• A change in the gene pool of a population over time
• Anything that causes a change in the gene pool is an example of evolution
• Each type of living organism is a result of millions of years of the slow evolution
process
• Process is very slow with evidence to support the scientific theory that evolution
has taken place
, CREATION VS SCIENTIFIC IDEAS ABOUT ORIGIN &
VARIETY OF LIVING ORGANISMS
CREATION IDEAS SCIENTIFIC IDEAS
- Cultural or religious ideas - Based on observations or experiments
- Creation story handed down from
generations through a source
- Source: Traditional storyteller OR holy
book
- Accepted without question - Questioned & investigated to check
- Cannot be investigated by direct validity
observation
- Not based on evidence - Based on evidence available at the time
- Special to 1 culture or community - Accepted by different cultures
worldwide
- Do not change - Change with new information &
evidence
Different Kinds of Evidence
THE FOSSIL RECORD
- People have found many examples of fossils:
- Fossils are signs that life existed in the past
- Petrified remains of species that do not exist & species similar to modern types show
that forms of life have changed with time
,FOSSILS TELL US ABOUT THE ORIGIN OF VARIOUS SPECIES BECAUSE:
1. Fossils are usually found in rocks in strata [layers]:
- Thus they show an order of development
- E.G: earliest fish found below early amphibians, below early reptiles, below early
birds & mammals
2. Transitional fossils found show the steps in the changes needed to produce modern
structures
- E.G: Fossils show development of the leg of the modern horse
• One toe from earlier ancestors that were the size of a dog & had 5 toes
MODIFICATION BY DESCENT
- The passing of characteristics from parents to their offspring
• Hereditary
- New characteristics appear & lead to modification in the gene pool of the population
- New characteristics appear because:
1. Genes from 2 different organisms have combined through sexual reproduction
2. Gene or chromosome mutation has happened
- Result is that each new generation descends from the previous one by modification
of genes in its gene pool
• There has been descent with modification
- Genes found in a population of organisms change constantly
- Individuals with set of genes that make them well suited to their ecological niche
will pass favourable genes to the next generation
• Each generation’s descendant population becomes modified from parents
- Possible to trace origin of specific modified characteristics
• E.G: foot of modern horse that enables it to run quickly evolved from pentadactyl
limb found in all vertebrate animals
BIOGEOGRAPHY
- The study of the distribution of species around the world
, - Different animals & plants are found in similar habitats in different parts of world
- Southern Hemisphere:
• Continents have similar habitats
- Hot grassy plains
• Have completely different large flightless birds
- Different birds come from different origins & have independently changed with
time to suit their habitat
- Different species adapt to suit similar habitats
• Appear similar because characteristics evolved to suit the particular environment
• Happens even if they are not related
- 1835: Charles Darwin visited the Galapagos Islands in Pacific Ocean off coast of
Ecuador
- Found that each island had its own type of giant tortoise
- West, grassy areas on larger Islands
• Domed shells
- Smaller, drier Islands
• Saddleback shells
- Allowed tortoises to stretch necks to eat from bushes & cactus
- Darwin questioned if origin of all different kinds of tortoises was that a different one
was created for each island
• More likely that the original type of giant tortoise had adapted to suit different
conditions of each island
- Genome of original species on each island was modified with time
GENETICS
- A process of evolution:
• Mutations cause variations in a population that can alter the frequency of genes in
a population
- Evolution works at level of genotypes & phenotypes
- Genetics explains:
1. How the variation that leads to change happens
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