Elevate your understanding of human evolution with our concise and easy-to-follow study notes, designed specifically for students. This resource simplifies complex topics like the origins of humanity, natural selection, and major evolutionary milestones, making it perfect for exam prep or homework ...
General Terminology
Bya - Billion years ago
Mya - Million years ago
At least 5 mass extinctions have occurred
By studying fossils, you learn about ancient forms, changes in life forms and gain evidence
that species change.
South Africa is very rich in fossils
Microevolution: small scale changes occurring within a single species from one
generation to the next. It may occur by natural selection or genetic
drift
Macro evolution: Large scale change – development of new life forms over many
Generations. Resulting in the large groups of organisms over long
periods of time
Gene flow: flow of genes from one population to a related population when
individuals of each interbreed.
Genetic drift: this implies a shift in gene frequency (abundance) in a population.
Some genes may become more abundant in a population and others less so.
Founder Effect: A few members of the population become isolated from the parent
population or are introduced to a new environment. This can result in a gene pool that may
not contain the same portion of alleles for a particular region on a chromosome as is found
in the original population. This may result in over-representation of a particular gene in the
populations that result from inbreeding in this founder population. For EXAMPLE:
Huntington's Disease, for example, is more common among the Afrikaner or Dutch-descent
population of South Africa than in most other populations, because a gene for Huntington's
happened to be unusually common among the small group of original Dutch colonists. The
Afrikaner population of South Africa is mainly descended from one shipload of immigrants
which landed in 1652. The early colonists included individuals with a number of rare genes.
The ship of 1652 contained a Dutch man carrying the gene for Huntington's disease, an
autosomal dominant disease which does not appear until the sufferer is over 40 years old
and leads to certain death within five to 10 years. Most cases of the disease in the modern
Afrikaner population can be traced back to that individual.
Evidence for the theory of evolution is supported by:
o Fossil records
o Biogeography
o DNA and genetics
o Homologies and comparative anatomy
o Embryology
o Vestigial organs
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, Using the above, scientists are able to:
1. Develop detailed histories of evolution in life forms
2. Show relationships between organisms alive and dead
1. Fossil records
Fossil records show descent with modification - oldest fossils found in the oldest layers of
rock. These fossils less diversity. Later fossils show greater diversity. Therefore biodiversity
increased.
Modern species can be traced back through time as show similarities with older fossils
From the fossil record the following can be seen:
Simplest organisms appear first in fossil record
Increase in diversity: Cladogram
More extinct species as one moves back in time
Intermediate forms between groups (transitional fossils) are found. Transition fossils have a
mixture of traits that show a link between groups and are often referred to as the missing
link. They suggest that one group may have given rise to the other by evolutionary
processes.
Overall increase in size, from starting point to unicellular organism
Simpler to more complex Millions of years since first known
appearance (Mya)
Earth began… 4600
Oldest fossils 3600
Oldest eukaryotic cells 2000
Multicellular eukaryotes 1500
Simple animals (invertebrates) algae 600
Fish and land ferns 450
Amphibians 350
Reptiles and cone bearing plants (gymnosperms) 250
Birds 150
Mammals and angiosperms 100
Modern humans 0.2
Cladogram: a family tree that shows evolutionary relationships. Similar to a pedigree
diagram. Examples will be looked at.
Do fossil records provide conclusive proof of evolution?
In many ways the fossil record is incomplete because:
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