Evolution and Origin of Life Theories

• Evolution is a change in the genetic composition of a population over generations.
• It's caused by meiosis, hybridization, natural selection, or mutation.
• This leads to divergence from other populations and potentially the origin of new species.

Origin of Life

• The origin of life refers to the emergence of heritable self-reproduction.
• Opposing theories include intelligent design and creationism.
• Complex life forms evolved from simple bacteria-like cells through self-organization.
• Multiple theories exist regarding the origin of life.

Theories on the Origin of Life

• Special Creationism: Life was created by a supreme being.
• Spontaneous Generation: Life can emerge spontaneously from non-living objects.

Scientific Experiments Disproving Spontaneous Generation

• Francesco Redi's experiment with meat and maggots discredited spontaneous generation.
• John Needham's experiment with boiled broth and microorganisms supported spontaneous generation.
• Lazzaro Spallanzani's sealed flask experiment revealed the importance of air in growth
• Air in sealed flasks destroyed its ability to support life
• Louis Pasteur's experiment demonstrated broth/wine only went sour if microorganisms entered.
• No microorganisms appeared if they were sealed from the outside.
• Pasteur used swan-neck flasks, allowing air exchange but preventing airborne microorganisms.
• Sterilized broth in intact swan-neck flasks remained sterile.
• Broken necks led to microbial contamination and growth.
• Pasteur proved life arises only from pre-existing organisms, demonstrating life can only arise from pre-existing organisms
• If life is not eternal and has a beginning, there must have been a first cell, though it could not have come from a pre-existing cell.
• Eternity of Life: Life has always existed and does not need special creation.
• Supporters believe life is an inherent property of the Universe.
• Some scientists believed this theory because they thought the Universe was unchanging.
• Cosmozoan Theory/Panspermia: Life reached Earth from other structures like meteorites, as resistant spores.
• Biochemical Origin Theory: Life evolved via reactions on Earth
• Organic molecules formed with an external energy source.

Evolution of Early Life Forms

• Autotrophs form the basis for all food chains, creating organic materials
• The first organisms were prokaryotes without a true nucleus.
• Three distinct lines of evolution emerged: Archaebacteria, Eubacteria, and Eukaryotes.
• The shift to an oxygen-containing atmosphere was a significant change in early life forms.

Types of Autotrophs

• The two major types of autotrophs are
• Chemoautotrophs:
• Organisms obtain energy from a chemical reaction (chemotrophs).
• Carbon source is carbon dioxide.
• Found in extreme habitats, they are the oldest organisms on Earth.
• Photoautotrophs:
• Organisms use light as their energy source.
• Use inorganic energy sources like ferrous iron, hydrogen sulfide, or ammonia.
• Use CO2 as their source of carbon.
• All chemoautotrophs absorb energy through chlorophyll molecules
• Typically found in the Archaea or Bacteria domains.

Theories of Evolution

• Lamarckism:
• Proposed by Jean-Baptiste De Lamarck (1744-1829).
• Explains the diversity of modern organisms and the fossil record
• Highlights the inheritance of acquired characteristics.
• New needs.
• Use and disuse of organs.
• Inheritance of acquired characteristics.
• Speciation drive evolution.
• Inheritance of acquired traits:
• Traits acquired during an individual's lifetime can be passed on to offspring.
• Disproved by discoveries in genetics.
• Explains vestigial organs and relatedness of different species.
• Significance of Lamarckism:
• First comprehensive theory of biological evolution.
• Explains the existence of vestigial organs.
• Explains the development of strong jaw muscles and claws in carnivores.
• Stimulated other biologists to look for evidence of evolution.

Charles Darwin (Theory of Natural Selection)

• English naturalist (1809-1882).
• Influenced by Alfred Russell Wallace and Charles Lyell.
• Collected evidence during his voyage on the HMS Beagle, including a visit to the Galapagos Islands.
• Studied the finches on the islands and observed variations in their beaks.
• Formulated the theory of natural selection.

Basic Postulates of Darwinism

• Geometric Increase: Species produce more offspring than can survive.
• Struggle for Existence: Competition due to limited resources.
• Variation Under Nature: Differences among individuals of a species.
• Natural Selection or Survival of the Fittest: Individuals with advantageous traits survive and reproduce.
• Origin of Species: Over time, new adaptations lead to the emergence of new species.

Neo-Darwinism Theory

• Includes knowledge of genetics and gene action/origin of species/
• Considers the gene pool of a population in terms of all available alleles.

Postulates of Neo-Darwinism

• Genetic variability
• Natural selection
• Reproductive isolation

The Evidence for Evolution

• Comparative Anatomy:
• Strong evidence for evolution.
• Structural similarities of organisms determine evolutionary relationships
• Homologous structures show evolutionary relationships & common ancestors
• Analogous structures have the same function but different structures, so don't indicate common ancestor.
• Comparative Embryology:
• Studies embryo development of vertebrates.
• Similarities support common ancestry.
• All vertebrate embryos have gill slits and tails early but have different fates.
• Palaeontology:
• Studies fossils to establish similarities and differences between organisms.
• Fossils provide evidence for evolution and ancestry
• Can be remains, imprints, or intact structures.

Fossils can be categorized into two types:

• Category 1: remain of dead animal /body fossils
• Category 2: something that was made/ trace fossils
• Body fossils are the actual and trace fossils are made by an animal.

Dating Fossils

• Stratigraphy - sedimentary rocks are laid down in layers (strata) that help determine the age of fossils.
• The oldest strata and fossils are found in the lowest layers, and more recent rocks and fossils are found in the upper layers.
• Radiometric dating measures the abundance of parent and daughter isotopes in a sample.
• Relative dating establishes the age of one thing relative to another based on their relative order.

Methods of dating Rocks

• Radiocarbon dating: decay of radioactive carbon into nitrogen atoms.
• Potassium-argon dating: decay of radioactive potassium into argon atoms.
• Both methods have half-lives, with each half-life resulting in a decay of 50% of the radioactive atoms.
• Comparative Biochemistry:
• Organisms with similar molecules and biochemical pathways are closely related.
• Analyzing DNA and protein sequences determines evolutionary relationships
• Humans share 98% of their DNA with chimpanzees.
• Haemoglobin, found across animals, has variations that indicate evolutionary relationships.
• Haemoglobin analysis cannot include plants and algae.

Natural Selection

• Is the driving force behind evolution
• It leads to populations changing (over time), eventually leading to speciation.
• Adapted members of a species survive and reproduce more.
• Advantageous types increase in frequency. Species can interbreed and produce offspring

Types of Natural Selection

• The different types of natural selection work in the same manner, but their influence on a population is different
• Directional.
• Stabilizing.
• Disruptive selection.
• The spread of antibiotic resistance in pathogenic bacteria exemplifies evolutionary adaptation.

Patterns of Evolution

• Divergent Evolution:
• Two species gradually become increasingly different.
• Occurs when related species diversify to new habitats.
• Responsible for the diversity of life from the first cells.
• Responsible for human/ape evolution from primates.
• Convergent Evolution:
• Unrelated organisms evolve similar traits due to similar environments/niches.
• Occurs when different ancestries share analogous traits due to the environment.
• Example: Whales and fish swim through the water.
• Parallel Evolution:
• Species independently evolve, staying at the same similarity level.
• Typically between unrelated in different habitats.

Types of Speciation

• Natural selection provides a mechanism for speciation.
• Speciation involves forming new species via isolating mechanisms preventing interbreeding.
• The two main ways are:
  • Allopatric: Populations are separated by geographical barriers and independently.
  • Sympatric: Populations independently without geographical barriers.

Polyploidy in Plant Evolution

• Multiple sets of chromosomes.
• Allows infertile hybrids to become fertile, leading to new species formation.
• Reproductive Isolation:
• Prevents gene flow between two species:
• Prezygotic: before zygote formation.
• Ecological (or habitat) isolation: differences in habitat.
• Temporal: differences in mating times.
• Behavioral: courtship behavior differences.
• Mechanical: Male and female parts do not fit.
• Gametic: sperm can't fertilize egg.
• Postzygotic: after zygote formation.
• Hybrid Inviability: Hybrid embryo dies before reaching reproductive maturity.
• Hybrid Infertility: Hybrids are sterile.
• Hybrid Breakdown: offspring have abnormalities that reduce their fitness.

Human Evolution

• There is a 'line of evolution' for millions of years that has given rise to old world monkeys, new world monkeys, great apes, and different species of humans
• Humans (Homo sapiens) are the latest species of humans
• Two features that distinguish humans from other primates are:
• Humans (Homo sapiens) have a very large brain and bipedalism

Important Fossils in Human Evolution

• Lucy: dated at about 3.2 million years, belonged to Australopithecus afarensis
• had a brain about the same size as a chimpanzee and was bipedal
• Ardi: 1.2 million years older than Lucy.
• belonged to Ardipithecus ramidus, was also bipedal and is the nearest fossil to the 'common ancestor' of humans and chimpanzees.
• Studies on brain size show it has increased
• Lucy and Ardi helped understand evolution of humans and chimps.
• Branching points create new populations
• All humans are in the genus Homo.
• Small groups discuss differences among the human races.

Increase in Cranial Capacity in Hominid Species

• Species of Australopithecus have a brain that is between 0.7% and 1.0% of their body mass, whereas modern humans have a brain size between 1.8% and 2.3% of their body mass
• Brain of Homo sapiens uses 25% of the resting energy requirement, compared with 8% in the great apes
• Advantages of a larger brain allows humans to run faster and in a more upright posture, plan in advance to avoid attack, and develop and use tools and weapons
• Homo sapiens first appeared in Africa and have since migrated to all other parts of the world
• Different environments encountered by humans have resulted in different human populations evolving along different lines
• Examples of body features that gave a survival advantage in colder climates include a shorter, squatter body shape, an increased layer of adipose tissue under the skin, and increased hairiness
• Mutations
• can be caused by several factors and is divided into two parts:
  • spontaneous mutation
  • induced mutation
• Substances that cause mutations are radiation, x-ray, ultra-violet radiation, nuclear radiation, and certain chemical substances
• Changes involving only a single base are called point mutations

Point Mutation

• A change in a single nucleotide in DNA
• usually less serious than a chromosomal alteration (changes UUU to UCU)
• Types of Point Mutation:
• Substitution: one base replaces another.
• Addition: an extra base is added.
• Deletion: a base is 'missed out' during replication.
• Effects of Point Mutation:
• A single base change can dramatically affect the resulting protein.
• Substitutions may result in a different protein being.
• Addition and deletion mutations can cause frame shift mutations, resulting in a non-functional protein or no protein at all.
• Frame shift Mutation occurs when there is one fewer or one extra base, causing the whole sequence after the mutation to be altered.
• It results in a totally different mRNA and a non-functional protein or no protein at all

Chromosomal Mutation

• A mutation involving a long segment of DNA
• It occurs when there is any change in the arrangement or structure of the chromosomes
• usually more serious than point mutations and can result in the death of a cell or affect the whole organism
• Types of Chromosomal Mutations:
• Duplication/Amplifications: An extra copy of a segment or the entire chromosome is present in the nucleus, also known as partial trisomies.
• Deletion: A piece of a chromosome is removed or deleted, also known as partial monosomies.
• Inversion: A segment of the chromosome is reversed from end to end.
• Paracentric inversion: When the inversion does include the centromere
• Effects of Chromosomal Mutations:
• Chromosomal mutations create fusion chromosomes by fusing one type of chromosome with another one.
• Chromosomal mutations can result in missing genetic information, extra genetic information, or rearrangement of genetic information
• Consists of aneuploidy and polyploidy, both of which cause a mutation by changing the number of chromosomes present in the cell
• Belongs is under the category of heteroploidy

Aneuploidy and Polyploidy

• Aneuploidy:
• Chromosome loss/addition due to chromosome contortion
• Polyploidy:
• Creation of two sets of genomes.
• Not common naturally, but can observed.
• Can cause giantism and reduced fertility.

Advantages/Disadvantages of Chromosomal Mutations

• Can benefit the organism in some cases/better survive
• Can be dangerous/detrimental to life
• Genetic disorders
• Disabilities caused by mutations within the organism.
• Specific disorders or disabilities caused by mutations within the organism. Can be small or large issues
• Specific disorders or disabilities caused by mutations within the organism

Genetic Drift

• Mechanism where allele frequencies change through generations via chance.
• Altered due to "sampling error" in selecting next gen alleles from current gen.
• Can increase/decrease allele frequency by chance alone

Population Size Affect

• Genetic shift is independent of population size, though rapid in small populations.
• Large populations have more alleles but lose them more slowly
• Assumes mutations consistently add alleles and selection is paused

Hardy-Weinberg Equilibrium

• Allele frequencies do not change from one generation to the next
• Only occurs assuming no natural selection/mutations/migration/random changes

The Genetic Bottleneck Effect

• Genetic drift occurs due to population size reduction (like a disaster)
• Pre-disaster allele frequencies are very different
• The smaller population will have an increase in genetic drift over generations
• Founder Effects
• Genetic drift occurs when a small group forms a colony from a group of individuals
• The separated colony will be isolated
• Small size causes genetic drift in the new colonies

Gene Flow

• Any movement of individual/genetic material between populations
• Variation source Immigration is new organism(s) joining a population Emigration is members leaving taking genes with them

Causes of Extinction

• Natural / anthropogenic disasters Played a role in direct and indirect causes

Explore evolution as genetic change over generations, driven by meiosis, hybridization, natural selection, or mutation. Discover the origin of life through heritable self-reproduction and theories like special creationism and spontaneous generation. Learn about experiments disproving spontaneous generation.