Evolution - The Evidence

Alfred Wallace

Independently published a similar theory to Darwin, based on his observations in Indonesia. However, Darwin was credited with the better theory as he had more evidence compared to Wallace. Darwin had developed his theory 15 years before publishing, however the theory is often referred to as the Darwin/Wallace Theory of Evolution by Natural Selection due to Wallace's contribution

Theory of Evolution big ideas

• The theory of evolution states that life forms on earth have genetically changed with time. Different species have gradually developed in response to changing environments. These changes have usually occurred slowly over millions of years

• Over time species have not remained constant – they have changed. New species have arisen and others have become extinct

• There has been a general change of simple to more complex forms of life

Evidence for evolution

• Fossil Evidence

• Comparative Embryology

• Comparative Anatomy

• Biogeography

• Biochemical Evidence

How do fossils support the theory of evolution?

• Provides a record of the development of species that once existed over time

• Evolutionary stages can be represented by a change in the species physical appearance in fossils over a long period of time (gradual change)

Examples of fossil evidence supporting the theory of evolution

• Vertebrates: the chronological appearance of different vertebrates in the fossil record is supported by other types of animals

  • Early species of fish had no legs, but developed them in their transition to land, creating amphibians. Amphibians would turn into reptiles, reptiles to birds and so on

  • All occuring from 500mya to 150mya

• Transitional species: an intermediate species between two different species. The theory that organisms develop from each other or a common ancestor is supported by many transitional forms

  • Archaeopteryx who has the features of both a reptile and a bird

Relative Dating

Involves looking at which layer of sedimentary rock a fossil is found in. Comparisons can be made to nearby rocks of the same type

Absolute Dating

Uses the proportion of radioactive isotopes to quantitatively determine the age of a rock/fossil (C-14 dating, Argon-argon dating)

Comparative Embryology

The science of observing similarities and differences in the structure of vertebrate embryos at different stages of development

How does comparative embryology support the theory of evolution?

• Suggests species had a common ancestor, by their embryos being similar in structure in very early stages in life

• The more alike the embryos at later stages of development, the more closely related the species

Examples of comparative embryology supporting the theory of evolution

Shark, lizard, chicken, pig and human embryos are similar in structure, having gill slits, a tail and notochord in early developement

Comparative anatomy similarities

• Modern day vertebrates have a similar ‘basic’ structure of their vertebrate forelimbs called homologous structures

• A human, cat, whale, bat, bird, lizard and frog each share the same five part structures in their arms

Comparative anatomy differences

• The common ancestor to these species was likely isolated in different environments, and have adapted over time to form new species as a result of different selection pressures

• Each species uses its vertebrate forelimb for a different purpose/environment

• Structure reflects function

How does comparative anatomy support the theory of evolution?

Suggests species had a common ancestor, by features of the body being similar in structure

Examples of comparative anatomy supporting the theory of evolution

The presence of a humerus, radius, ulna and phalanges in a range of species (human, frog, lizard, bird, cat, whale, bat). The structure/placement of these bones in these species is the same, however vary in size and shape

Whale comparative anatomy example

• Function: Forelimbs act as flippers, heloing it swim easily and stabilise its body and aid in its turns

• Structure: The humerous, ulna and radius are shorter and more dense, providing strength in the arm. The phalanges are longer in comparison, to aid steering

Vestigal structures

Structures that have no apparent function and are ‘residual’ organs/structures from a past ancestor

How vestigal structures support the theory of evolution

• Provides evidence for evolution as these structures, as they serve no purpose however are present in the organism

• It would be wasteful to continue to provide resources to these structures, therefore the environment tends to favour those with reduced versions or without these structures

Examples of vestigal structures

• Wings on flightless birds

• Legs on snakes

• Human tailbone

• Pelvic bone on whale

Biogeography

The study of how plants and animals are geographically distributed on different continents

How does biogeography support the theory of evolution?

Suggests species evolved from a common ancestor when geographically separated, which placed different selection pressures on them, causing them to evolve

Examples of biogeography supporting the theory of evolution

• Darwin’s Finches: where the birds beak sizes changed as a result of changing environment and selection pressures, believed to have shared a common ancestor

• Flightless birds: different flightless birds are located continents that were once part of Gondwana and are theorised to have a common ancestor (emus, ostriches, cassowary, kiwi)

How does biochemical evidence support the theory of evolution?

Suggests species had a common ancestor, evident in the presence of similar genetic code. The more similar the DNA, the more likely they share a common ancestor

Examples of biochemical evidence supporting the theory of evolution

Structures of amino acid sequences in our DNA. Sequences present in species which have common proteins and in similar sequences will be more closely related

Basic structure of genes and protein

• Nucleotides with different bases of adenine (A), thymine (T), cytosine (C) and guanine (G)

• The number, types and order of the bases determined what amino acid is produced

• The order of amino acids determined the type of polypeptide chain and therefore protein that is produced

Amino acid sequencing

Observing and analysing the similarities in the sequence of amino acids which male up common proteins found in a range of organisms

Example of amino acid sequencing

Cytochrome C: a protein involved respiration that is common to all aerobic organisms from bacteria to plants to animals

• Humans and chimpanzees share 100% of their cytochrome C amino acids

• Humans and rhesus monkeys share all but one

• Less so with dogs, snakes and tuna

Antibiotics

A class of drugs used to treat bacterial infections/diseases

Example of antibiotics

Pencillin - A broad-spectrum antibiotic, first produced by the Pencillium fungi. They work by damaging the bacteria’s cell wall, resulting in a build-up of pressure so it bursts (therefore it cannot reproduce)

Antibiotic Resistant Bacteria

Bacteria that have been able to evolve in response to the use of medicines, meaning they are unable to be treated

How does antibiotic resistant bacteria relate to natural selection/evolution?

1. Within every population there is variation. Some bacteria will be resistant to antibiotics

2. When treated with an antibiotic, those that are not resistant will die (antibiotics act as a selection pressure)

3. These ‘resistant’ bacteria are able to survive and reproduce, passing this ‘resistance’ onto their offspring

Evolution in cane toads

• Over time there is has been an increase in leg length for cane toads

  • Resulting in an increase endurance

  • Resulting in travelling approximately 0.5 km more per day

• In the 1930s they were spreading at approximately 15 km/year, current estimates suggest up to 60 km/year in distribution spread

• Comparisons between toads in NT and QLD

  • Move more, longer, stronger legs, travel at night, physically larger

How do cane toads relate to natural selection/evolution?

• Lack of selection pressures enable them to repoduce

• Toads with favourable characteristics survive (Larger, longer legs, more toxins)

• Has also led to snakes (red belly black snakes) evolving to be able to consume smaller toads with less poison and are more likely to survive to eat more toads