Chapters

Evolution

Intro to Evolution

the process of cumulative change in the heritable characteristics of a population

Evolution

Jean Baptiste de Lamarck (1744-1829)

Russel Wallace (1823-1913) and Charles Darwin (1809-1882)

Players in Evolution

A process in nature in which organisms possessing certain genotypic characteristics that make them better adjusted to an environment tend to survive, reproduce, increase in number or frequency, and therefore, are able to transmit and perpetuate their essential genotypic qualities to succeeding generations.

Natural Selection

Fossil Records

Artificial Selection

Homologous Structures

Evidence for Natural Selection

Too many offspringover production of offspring leads to intra-species

competition and survival of the individuals best suited to that particular environment.

competition can also lead to adaptive behaviours.

Natural Variation in a Population random assortment of chromosomescrossing over of segments of chromosomes result in

new combinations of genes, different than the parental combinations

random fusion of gametes in sexual reproductionadditional variations arise due to mutations, either

chromosomal or gene

Mechanisms of Evolution

The favourable characteristics are expressed in the phenotypes of some of the offspring

These offspring may be better able to survive and reproduce in a particular environment; others will be less able to compete successfully to survive and reproduce.

ExamplesAntibiotic Resistant BacteriaPeppered MothHeavy Metal Tolerance in Plants

Natural Selection Summarized

Evolution and the Origin of Life

Biologists believe that organic evolution by natural selection accounts for the major steps in evolution.

macroevolution – major developments such as the origin of the eukaryotic cell, the origin of multicellular organisms, and the origin of vertebrates from non-vertebrates

microevolution – the relatively minor changes that arise and lead to the appearance of new, but closely related species.

Theory of evolution - the Big Bang.

Introduction

Chemical Reactions to produce simple organic molecules, from inorganic molecules

Assembly of the molecules into polymers

Self Replication of Polymers

Development of Membranes to enclose the polymer

Four Processes for the Spontaneous Origin of Life

Heat, Temperature and Lightning – Miller and Urey Experiment

Recreated ancient atmosphere (nitrogen, water vapour and carbon dioxide, smaller amounts of methane, ammonia, carbon monoxide, sulphur dioxide, hydrogen sulphide and hydrogen cyanide.

Lightning and UV radiation to provide energy

Chemical Reactions to Produce Simple Organic Molecules

Other Possibilities

In Space – Panspermia

Alternating Wet and Dry Environments

Near Volcanos

Deep Sea and Ocean Vents

Chemical Reactions to Produce Simple Organic Molecules

As the organic compounds are made, they arrange themselves in lines – polymers (Using the Clay Lattice as a template)

Lines of molecules form early enzymes (ribozymes)Catalyse reactions, such as peptide bond formationRNA strand is made and due to enzymes, a

complementary strand can be made, and then copies are made

Longer and longer double stranded pieces are made, forming , now DNA

DNA more useful as it is longer and can hold more information (RNA – 1500 nucleotides max)

Formation of Polymers and Self-replication - RNA

Membranes were needed to separate the external environment from the internal environment

Phospholipids would have formed and due to hydophilic and hydrophobic properties, would form spheres in water (called coacervate)

Due to the bilayers, an internal environment would form, and if the early molecules (RNA to DNA) were trapped in the membrane, protobionts would have formed

Development of Membranes - Protobionts

Early cells were anaerobic and heterotrophs

As nutrients decreased in amount, some evolved to become chemoautotrophic, using the gases in the air

Since there was a large amount of CO2, some early prokaryotes used the gas, to produce early carbohydrate. The waste product was O2, which went into the atmosphere

Prokaryotes and the Oxygen on the Atmosphere

The formation of an ozone layer in the upper atmosphere commenced

The ozone layer began to reduce the incidence of UV light reaching the Earth’s surface.

Terrestrial existence (rather than life restricted to below the water surface) became a possibility

Other prokaryotes, simply ‘fed’ on the organic molecules available in their environment.

The bacteria had evolved aerobic respiration and so had the enzymes not only of glycolysis, but also of the Krebs cycle and terminal oxidation.

Prokaryotes and the Oxygen on the Atmosphere (continued)

Endosymbiotic Theory

Species and Speciation

Gene Pool – all of the genetic information present in the reproducing members of a population at a given time

Allele Frequency – is a measure of the proportion of a specific variation of a gene in a population. The allele frequency is expressed as a proportion or a

percent, and can be calculated by the Hardy-Weinberg equation (more later).

For example, it is possible that a certain allele if present in 25% of the chromosomes studied in a population. One quarter of the loci for that gene are occupied by that allele. Keep in mind it is not the same as the number of people who show a particular trait.

Definitions – Neo - Darwinism

Evolution = Change in Allele Frequency

Species

Morphological DefinitionA type of organism that has fixed

characteristics that distinguish it from all other species

Biological DefinitionGroup of actually or potentially interbreeding

populations, with a common gene pool, which are reproductively isolated from other such groups

Species and Speciation

Speciationthe evolution of new species, requires that

allele frequencies change with time in populations.

Mechanisms = Isolation

Geographic (Allopatric)Temporal (Sympatric)Behavioral (Sympatric)

Species and Speciation

Geographical Isolation (Allopatric)Ex. Galapagos IslandsEx. SnailsLizards

Species and Speciation (Animation)

Temporal (Sympatric)Ex. Plants and Apple Maggot Fly

Behavioral (Sympatric)Ex. Konrad Lorenz and the GwanMovie

Hybrid Infertility

Species and Speciation

Adaptive Radiationmany similar but distinctive species evolve

relatively rapidly from a single species or from a small number of species.

Species and Speciation – Trends in Evolution

When the species evolves different ways, this is called DIVERGENT EVOLUTION

The new species is different than the first, in terms of the adaptations that have taken place

Species and Speciation – Trends in Evolution

Living organisms often find the same solution to particular physiological problems, and as a result the organisms, in response to their environment, can become morphologically similar, even though they are not related to a common ancestor.

This is called CONVERGENT EVOLUTION

Species and Speciation – Trends in Evolution

Species and Speciation – Rates of EvolutionGradualism Punctuated

Equilibrium

Transient Polymorphisms

When there are two alleles for a gene in the gene pool, it is called polymorphic.

If one allele is gradually replacing the other, based upon environmental pressures, this is called balanced polymorphism

Ex. Peppered Moth (Biston betularia)

Species and Speciation

Balanced Polymorphism

When two alleles of a gene can persist indefinitely in the gene pool of a population

Ex. Sickle Cell Anemia

HbN HbN – normalHbn Hbn - Sickle Cell anemic but immune to

malariaHbN Hbn – heterozygous, slight anemia, but

resistant to malaria

Species and Speciation

Human Evolution and Origins

Humans are known as Homo sapiens (modern man). The full classification is:

Kingdom: AnimaliaPhylum: ChordataSubphylum: VertebrataClass: MammaliaSubclass: EutheriaOrder: PrimatesSuborder: AnthropoidsFamily: HominidaeGenus: HomoSpecies: Sapiens

Human Evolution

Use Fossil Records as evidence

Use Carbon – 14 Dating to see how old the fossil or artefact is.

For C14, the half-life is 5730 years.

For fossils and rocks older than 60 000 years, we use K40 dating.

Human Evolution

What defines humans as primates?

Opposable Thumbs for grasping

Mobile arms with shoulder joints allowing movement in three planes and the bones of the shoulder allowing force to be applied to the arms.

Stereoscopic vision

Skull Modified for upright posture – Magnum foramen

Human Evolution – Humans as Primates

Ardipithecus ramidusLived approximately 5.8 – 4.4 mya in Ethiopia

Trends in Hominid Fossils

AustralopithecinesA. afarensis from the Afar desert (4-2.8 mya) A. africanus (3-2 mya) found in South Africa. A. robustus (2-1.4 mya) in South Africa.

Trends in Hominid Fossils

A. Africanus

Trends in Hominid Fossils

Homo genus. They were from around 2 mya and had larger brains (600

cm3) and walked upright.

H. habilis (handy man). thought he arose from A. afarensis 2 mya in East Africa and used simple tools.

Homo erectus was from Africa. It is thought it migrated to other parts of the world and had a larger brain than H. habilis.

H. neanderthalensis, which lived in Eurasia from 200 000 to 30 000 years ago

Next was H. sapiens, which came to Europe.

Trends in Hominid Fossils

H. Habilis

Trends in Hominid Fossils

H. Erectus

Trends in Hominid Fossils

H. Neadrathalis

Trends in Hominid Fossils

Trends in Hominid Fossils

Hominid Diets and Brain Size

Australopithecus brains were only slightly larger in relation to body size than the brains of apes.

Powerful jaws meant a largely vegetarian diet.

2.5 mya, Africa became drier, led to an evolution for survival, as there were less plants

Tools to hunt, increased supply of protein correspond to the changes in brain size

Trends in Hominid Development

Hominid Diets and Brain SizeThe correlation between the change in diet and

the increases in brain size can be explained in two ways

1. Eating meat increases the supply of protein, fat and energy in the diet, making it possible for the growth of larger brains

2. Catching and killing prey on the savannas is more difficult than gathering plant foods, so natural selection will have favoured hominids with larger brains and greater intelligence.

Trends in Hominid Development

Genetic and Cultural Evolution

In the recent evolution of humans, cultural evolution has been very important and has been responsible for most of the changes in the lives of humans over the last few thousand years.

This is much too short a period for genetic evolution to cause much change.

Some aspects of cultural evolution, ex. Medicine, have reduced natural selection between different genetic types and therefore, genetic evolution.

Trends in Hominid Development

Taxonomy and Classification

Classification

The process of classification involves giving every organism an agreed name and arranging organisms into groupings of apparently related organisms.

Scheme of the overall diversity of living things.

Classification attempts to reflect evolutionary links.

Classification and the Binomial System

The Binomial System

Carolus Linnaeus in the 18th Century

The first part of the name is the genus or the generic name based upon a noun.

The second name is the species, or the specific name, based upon an adjective.

Ex. Canis lupis – dog / wolf and grey /brindled coat

Classification and the Binomial System

Scheme of ClassificationKingdom – largest and most inclusive groupingPhylum / division – organisms constructed on a

similar planClass – a grouping of orders within a phylumOrder – a group of apparently related familiesFamily- a group of apparently related generaGenus - a group of similar and closely related

speciesSpecies – a group of organisms capable of

interbreeding to produce fertile offspring

Classification and the Binomial System

KingdomsProkaryotes –Examples are bacteria and

cyanobacteria Protista –Examples are Euglena and Paramecium Fungi –Examples are yeasts and mushrooms. Plantae –Examples are mosses, ferns, flowering

plants. Animalia - Examples are humans and jellyfish.

Classification and the Binomial System

Plantae Phyla

Bryophytes (mosses, liverworts)  Filicinophyta (ferns and horsetails)

Coniferophyta (cedars, junipers, fir, pine trees)

Angiospermophyta

Classification and the Binomial System

Animalia Phyla

Porifera (sponges)

Cnidaria (corals, sea anemones, jellyfish, sea jellies, hydra)

Platyhelminthes (flatworms)

Annelida (earthworms, leeches and polychaetes)

Mollusca (snails, clams, and octopi)

Arthropoda (insects, spiders, scorpions, and crustaceans (crabs, shrimp))

Classification and the Binomial System

Dichotomous Key

Classification and the Binomial System

Mathematics of Population at Equilibrium:Hardy-Weinberg Principle

A mathematical formula to detect change or constancy in gene pools

 The formula

For 2 alleles of a gene:

Use B for dominant, and its frequency in the population is p (a number between 0 –1)

Use b for recessive, and its frequency in the population is q (a number between 0 –1)

A gene must have an allele, with the options either B or b. No other options are available, so if B is present, it frequency is 1, and b is 0, therefore p + q = 1 (1+0)

Each gene has two alleles, so if the frequency of B is p, then BB is p2

If the frequency of b is q, then bb is q2

If you have Bb, the frequency is 2pq

Hardy-Weinberg Principle

Since genotypes must be one of the three, the percentage in a population will be:

p2 + 2pq + q2 = 1  

In order to be used, the following conditions need to be observed.

Large populationRandom mating occursNo directional selection (no advantage)No allele specific mortalityNo mutationsNo immigration or emigration

Hardy-Weinberg Principle

Hardy-Weinberg Principle

Phylogeny and Systematics

One of the objectives of classification is to represent how living and extinct organisms are connected, which means natural classification.

Phylogeny is the study of the evolutionary past of a species.

Species which are the most similar are most likely to be closely related

Species which show a higher degree of difference are considered less likely to be closely related.

Phylogeny and Systematics

Values to classifying this way.

Identify unknown organisms, as other similar organisms are grouped together using a key.

We can see how organisms are related in and evolutionary way. By looking at organisms, which have similar anatomical features, it is possible to see relationships on their phylogenetic tree. DNA evidence confirms the anatomical evidence for placing organisms in the same group.

It allows for the prediction of characteristics shared by members of a group.

Phylogeny and Systematics

Biochemical Evidence for Common Anscestry

Every known living organism on Earth uses DNA as its main source of genetic information

All the proteins found in living organisms use the same 20 amino acids to forms their polypeptide chains

All the living organisms on Earth have left-handed amino acids and none are right-handed, leading to the belief that there is a common ancestor.

Phylogeny and Systematics

If we compare the amino acid sequences of haemoglobin in humans, cats and earthworms, we see that cats and humans have greater similarities that humans and earthworms.

This shows several trends: The more similar the biochemical evidence, the more

interrelated the species are

The more similar the evidence, there is less time since the two species had a common ancestor (ie. The ancestor of earthworms lived a longer time ago than the ancestor of cats and human.)

Changes in the DNA sequences of genes from one generation to another are partly due to mutations and the more differences there are between two species, the les closely related they are.

Phylogeny and Systematics

1. AAAATTTTCCCCGGGG2. AAAATTTACCCCGGGG3. AAAATTTACCCGCGGG4. AACATCTTCCACGCTG

Phylogeny and Systematics

1 and 2 have the fewest differences in their DNA and are more closely related

Cladogram

Phylogeny and Systematics

Cladistics

Clades

Need to classify, taking into account:

Homologous Characteristics

Analogous Characteristics

Phylogeny and Systematics

Phylogeny and Systematics

BirdsFused clavicle

(wishbone)Flexible wristsHollow bonesCharacteristic egg

shellHip and leg

structure, notably with backward pointed knees

Shoulder girdleStrong skeletal

systemLay eggsLateral leg and hip

structure

Phylogeny and Systematics - Dinosaur

Reptiles