1. Theory and Evidence of Evolution
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Theories of Evolution
Early Ideas About the Origins of Life
All human cultures, from early times, tried to explain the origin of human beings and other living things on Earth. Each culture has a different story or creation myth. These stories generally share the view that species were created as they are now.
However, a number of early scientists found evidence that did not support this idea. Georges-Louis de Buffon, Jean Baptiste Lamarck, Charles Darwin and Alfred Wallace all generally share the view that all species have evolved from a common ancestor gradually.
Maori have the story of Earth goddess, papa and the sky god Rangi, who were joined so closely together that no light could come into the world and their children could not escape between them. One of their children, Tane managed to separate them.
Video: MAORI CREATION MYTH
The Christian story, of God making the world in six days and resting on the seventh, comes from the Old Testament. It was written down from the creation story passed down by word of mouth by Hebrew tribes.
Video: OLD TESTAMENT CREATION MYTH
Georges-Louis de Buffon
In 1760's Georges-Louis de Buffon proposed that all mammals must have come from a common ancestor after investigating the similarities in their limb bones.
Jean Baptiste Lamarck
In 1809 Jean Baptiste Lamarck put forward a theory to explain how changes in species could have come about.
He suggested that changes acquired during an organism's lifetime could be passed on to their offspring, causing a gradual change in the species (this gradual change is termed evolution).
In general, Lamarck's theory of evolution has not been supported by evidence except in the rather special case of some bacteria.
Charles Darwin & Alfred Wallace
Charles Darwin and Alfred Wallace both proposed a theory of evolution according to which species gradually change through a process called natural selection, where the individuals most fitted to their environment survive to pass on their characteristics to their offspring.
Darwin collected evidence over 20 years and published his work only when Wallace proposed a similar theory.
Darwin did not know about the role of genes and DNA played in inheritance, nor about the role of mutations in producing the variations upon which his theory depends.
What is Evolution?
In biology, the word 'EVOLUTION' refers to cumulative change in alleles within a gene pool over time. Although we will never now every detail of Earth's history, evidence points towards two absolute certainties:
The Earth is very old; about 4.6 billion years.
Living things change over time. We know that whole groups of animals and plants have become extinct, new species have appeared, and that the genetic make-up of species can, in some cases, change within a few generations.
The idea of evolution goes back more than 2,000 years. In 1859, Charles Darwin assembled many facts supporting the idea, and much more evidence for evolution has been discovered since then.
Darwin's Theory of Evolution
Darwin's theory of evolution by natural selection can be summarised as follows:
Present-day species have evolved from ancestral forms.
Organisms produce more offspring than survive. The offspring compete for food and other essentials in a struggle for survival.
Offspring produced by sexual reproduction will show variation; some will have characteristics that are more suited to the environment than others.
Those individuals of a species with favourable characteristics will survive longer and produce more offspring and so pass their favourable characteristics on. Those with unfavourable characteristics will not survive as long or reproduce as frequently. This is called the 'survival of the fittest'.
Successive generations will become modified over time, particularly if their environment is changing. Gradually, the species will change sufficiently to be recognised as a new species.
Modern Developments of Darwin's Theory - It's in our DNA
The modern definition of evolution involves changes in the gene pool of a population that over the generations lead to new types of organisms. The gene pool is the collection of all the genes of all members of a population.
Darwin believed that variations in parents were blended in offspring. This was a major flaw in his theory as it would reduce variation in a population. We now know this does not happen, as variations are coded for by genes, which are discrete (non-blending) units of inheritance.
We also know that variation is caused by:
Meiosis and sexual reproduction, which reshuffle chromosomes into new combinations.
Crossing over during meiosis, where pieces of homologous chromosomes swap segments containing the same genes but often with different alleles. This results in new combinations of alleles at different loci.
Mutations, which are changes in the DNA of genes. Mutations are the raw material that evolution works on. Only mutation can alter actual genes and produce evolutionary novelties. Most mutations are harmful and selected against immediately, some are neutral in their effect, and a few might confer a selective advantage on the organism. Some mutations occur spontaneously, wile others are induced by mutagens such as radiation (X-rays, UV rays), chemicals (benzene, nitrites, nitrosamines) and viruses. Some viruses may insert their DNA into the host DNA, resulting in mutations.
An adaptation is any inherited variation (structural, physiological or behavioural) that improves an organism's chances of passing on its genes to the next generation.
Genetic adaptations are different from physiological adaptations that individual organisms make during their lifetime in response to environmental changes - although the ability to make these changes may be inherited.
Evidence of Evolution
There are four types of evidence that we will explore:
Comparing DNA and protein
From Zealandia's separation from Gondwanaland 65 Mya, to the effects of the Ice Age and glacial periods on the sea level, to the effects of plate tectonics on New Zealand's landscape - the constant change in New Zealand's geography is key to shaping the range and diversity of species we see today.
BIOGEOGRAPHY is the study of the geographical distribution of species. Go through these slides and the 3 infographics below for more information on New Zealand's biogeography.
Importantly, there was a bottleneck event in the Oligocene, and species moved to fill vacant niches due to the lowering of the sea level as the climate began to cool and water was being stored in the polar caps and glaciers. New land was exposed and new niches became available. Different populations would have spread out and formed a cline where neighbouring populations were exposed to slightly different conditions and had slightly different selection pressures such as food sources.
Infographic: The rise and fall of New Zealand (Biozone)
Infographic: Warm INTERGLACIAL PERIODS (Biozone)
Infographic: GLACIAL PERIODS (Biozone)
Infographic: Which animals can colonise ocean islands? (Biozone)
Only certain groups of plants and animals tend to colonise oceanic islands.
The animals that successfully colonise oceanic islands have to be marine in habit or able to survive long periods at sea or in the air.
This is why bats and dolphis are the only native mammals in New Zealand.
Do Now in your OneNote/Notebook:
Which is the dolphin more closely related to: cows or sharks? Justify your answer!
FOSSILS are the remains of long-dead organisms that have been preserved and after many years, become part of the Earth's crust. Fossils provide a record of ancient organisms and the study of them provides evidence of lines of descent, showing us what the intermediate forms were like.
Infographic: Fossilisation - How fossils form (Biozone)
Comparing Anatomical Structures
HOMOLOGOUS STRUCTURES are features which are similar in structure and origin (as they likely evolved from a common ancestor) but have different functions (as they have evolved in different environments).
E.g. human arm and a frog arm
Whereas ANALOGOUS STRUCTURES are features with different evolutionary origins (meaning they are unrelated species with different ancestors) but have similar functions (as they have evolved in similar environments, exposed to similar selection pressures).
E.g. shark fin, penguin wing, dolphin flipper.
Infographic: Organisms with pentadactyl limbs share a common ancestor (Biozone)
Infographic: Analogous structures vs homologous structures
Comparing DNA Sequences
Comparing DNA sequence similarity between species can be used to measure relatedness. Studies comparing DNA sequences from different species (using techniques such as DNA sequencing or DNA hybridisation) has shown that even widely dissimilar species such as yeast and humans share most of the basic genes for biochemical processes, while more closely related species such as humans and chimpanzees have almost identical DNA. This indicates that all species currently living on Earth once had a common ancestor.
Mitochondrial DNA (mtDNA) found in the mitochondria can also be analysed to determine relatedness and when species diverged. Mitochondrial DNA:
Never undergoes crossing over
Is passed down the female/maternal lineage
Acquires mutations at a constant rate, so the presence of mutations in mtDNA can be compared to determine when species diverged.
Infographic: How is DNA used to compare similarities in sequence? Using DNA Hybridisation Technique.
Infographic: Similarity of human DNA to DNA of other primates
Comparing Protein Sequences
A protein has a specific number of amino acids arranged in a specific order. Any differences in the protein sequence reflect changes in the DNA sequence. Commonly studied proteins include blood proteins, such as haemoglobin, and the respiratory protein cytochrome C.
For example, there are no amino acid differences between the haemoglobin of humans and chimpanzees, indicating they recently shared a common ancestor. Whereas humans and frogs have 67 amino acid differences, indicating they had a common ancestor a very long time ago.
Infographic: Haemoglobin homology between humans and other animals
Full Summary of Scientific Evidence for Evolution
Tasks & Homework
Task: Continental Drift and Evolution
Optional Task: Videos
Task: Retrieval Grid
Worksheet: Cladograms & Phylogenetic Trees
Pages 174-175 – Speciation Events in New Zealand
Page 192 – Evidence for Evolution – Fossils
Page 193 – Evidence for Evolution – Biogeography
Page 194 – Evidence for Evolution – Comparative Anatomy
Page 195 – Evidence for Evolution – Analogous Structures
Pages 196-197 – Evidence for Evolution – Molecular Biology
Page 198 – Evidence from mtDNA and Y Chromosome Analysis
Education Perfect HOMEWORK
Work through the Education Perfect task called "B3.5 Concept 1: Evidence for Evolution"