A comprehensive, detailed study guide of all the Evolution content required for the IEB Life Science paper 1. This includes origin of ideas about origin, evidence of evolution, development of the theory of evolution, artificial vs natural selection, formation of new species, genetic recombination, ...
EVOLUTION NOTES:
● Evolution - a change over time
● Biological evolution - genetic changes in a population that are inherited over successive generations due to
natural selection and ultimately leading to the formation of new species
● Macroevolution - the development of new life forms or species from earlier life forms over many generations
(extend geological periods)
● Microevolution - the variation that occurs within a species. Small changes originate in the gene pool, resulting
in small changes in the genotype of the species that is passed on to the o spring
HYPOTHESIS VS THEORY
Hypothesis Theory
● An informed/educated assumption which ● A well-substantiated (supported by evidence) explanation or hypothesis that
provides a proposed solution to a problem makes sense of a natural phenomenon
of explanation of specific phenomenon, ● Based on scientific research and is usually tested and confirmed by
based on scientific evidence and independent groups of researchers (cited + same outcome)
observations ● It develops and is changed or replaced as new evidence is discovered
● EVOLUTION IS A THEORY
ORIGIN OF IDEAS ABOUT ORIGINS
● Origin and development of life on Earth is a great source of speculation and conflict
● Scientists support the theory that life on Earth arose from a common ancestor 4.6 billion years ago
● It is commonly accepted that the process of evolution occurred where one kind of organism changed into another
which led to the enormous biodiversity that currently exists on Earth
EVIDENCE OF EVOLUTION
1. Fossils - provide evidence of the history of extinct organisms on Earth. They give an indication of the climate
and environment millions of years ago
● Fossil record - the accumulation of all listed and known fossils of di erent ages that have been discovered by
paleontologists worldwide. It provides information about extinct species as well as species that are still living
today
● Scientists expect to find earlier, simpler fossils in the deeper, older rock layers and recent, more complex
fossils in the upper, more recent rock layers
● Older rock strata display less biodiversity than the more recent rock strata. This shows that there was an
increase in biodiversity over time
● The fossil record contributes to the compilation of a geological time scale from the origin of the earth until now
● Fossil records have many gaps, particularly in transitional forms where there is a change from one type of
organism to another
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, 2. Modification of descent - how the basic body plan and functions of organisms are modified and adapt to
di erent environments which is evidence of evolution
● Homologous structures - similar structures in di erent organisms with the same body plan that perform
di erent functions
● Similarities may be traced back to a common ancestor
● The changes/adaptations in the structure develop independently in each group according to the organism’s
habitat and mode of life (air/water/trees)
● Divergent evolution - the type of evolution where organisms develop from a common ancestor, but follow
di erent evolutionary paths
● Convergent evolution - organisms are not related, but develop structures for similar environments
completely independent of each other
● Analogous structures - body structures in di erent organisms that provide the same function, but did not
originate from a common ancestor
Modification within a species
● According to this theory, many species changed over millions of years to form species we know today
● These species are modified descendents of earlier species
● adaptations/modification occurred to adapt to di erent environments
3. Biogeography - the study of the distribution of existing and extinct plant and animal species in specific
geographical regions
● Prove that closely related species usually occur in the same geographical region and suggests that they may
have shared a common ancestor
● Biogeographical regions may have been isolated by barriers (large mountain ranges, large masses of water,
small landmasses, deserts), preventing species from spreading from one region to another. This may have led to
speciation
● The plant and animal life in di erent geographical regions with similar habitats and climatic conditions, but
separated by a geographical barrier, may also di er drastically (penguins - South Pole, polar bears - North Pole)
● This indicates that these species occurring in di erent geographical regions do not share a common ancestor
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, Flightless birds
● Flightless birds show great similarities although they live on di erent landmasses and belong to separate species
● Scientists claim that flightless birds may have developed from a common ancestor
● The birds were separated geographically when Gondwanaland broke apart
● Their climates and habitats changed as a result of continental drift and the birds adapted to their changed environments
● New species developed due to di erent mutations and selections in the various environments
4. Genetics - the study of inheritance which provides evidence for evolution
● Scientists study the DNA sequences of di erent organisms to determine evolutionary relationships - the greater
similarities between DNA sequences or organisms, the more recently they developed from a common ancestor
● Closely related organisms have more similarities in their DNA
● Explains the source of variation necessary for evolution to occur
● Shows how changes in genotype and phenotype are transferred to successive generations
● Explains how gene pools of populations change and lead to new species (speciation)
5. Other forms of evidence - Comparative biochemistry, vestigial organs, comparative embryology
● Comparative biochemistry - the molecular/biochemical composition of most living organisms is very similar.
This confirms Darwin’s idea that all living organisms have a common ancestor
● Characteristics used as evidence for a common ancestor:
○ Identical DNA structure in living organisms
○ Identical coding for protein synthesis (nitrogenous bases A, T, C, G)
○ Identical protein synthesis (transcription and translation)
○ Common set of 20 amino acids for building proteins
○ Same metabolic processes and enzymes
○ ATP as a universal energy carrier
○ Hox genes - master/control genes that determine development of body regions
○ Phospholipid membranes are common to all organisms
● Vestigial structures/organs - some organisms have structures/organs that, with disuse, may have decreased
in size over evolutionary times. They are often homologous structures that are still functional in other
organisms
● Provides evidence of a possible common ancestor
● Whales have no hind limbs, but have remains of a pelvic
girdle and under-developed hind limbs, suggesting a
four-footed ancestor. These structures do not necessarily
have no function, they just have a di erent function
(sexual reproduction)
● Comparative embryology - hypothesis proposed by
scientist Ernst Haeckel in the 1800s
● Embryos of various vertebrates share similar at various stages of development
● The similarities support the idea of a common ancestor and the theory of evolution
● Haeckel’s drawings were disproved by other scientists, thus his hypothesis is not used in support of the
evidence of evolution anymore
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