BIOL112 - Maartin’s Lectures

Biological evolution

Change over time, with or without the formation of a new species

Special creation theory

Things/species were created as we see hem and do not change - created separately. Earth and life are young

Evolutionary theory

Descent with modification - species change with time and derive from common ancestors. Earth and life are old.

Lineage

Succession of organisms connected to each other by ancestor-descendent relationships

Lineage succession

With time, organisms in a lineage change successively and gradually deviate increasingly from the original ancestors

Evolutionary biology

Science studying origin of organisms with new qualities and change within populations

Central claim of evolutionary biology

Modern life is a product of long evolution in the past - leads to testable predictions about future changes and undiscovered things

Why do we need to understand evolutionary biology? Importance?

Allows medical scientists to develop vaccines and predict/model how viruses may or may not change.

The theory of evolution explains

What has happened in the history of life on this planet and how this has happened

Anagenisis / cladogenesis

Types of speciation

Aim of anagenesis/cladogenesis

2 claims about life in the past that explain the origin of biodiversity. Both responsible for the origin and complexity and diversity of life.

Claim 1

If we take modern species and trace its lineage back in time, we will find organisms that deviate more and more from this species

Claim 2

If we take several modern species and trace their lineages back in time, we will see them merging one by one until eventually only one lineage remains - thus all species have common ancestry. Like branches on a tree

Anagenesis

Asserts that changes in one lineage happened. Over a long period of time, a species changes into something else until eventually the other species is no longer found

Cladogenesis

Asserts that splitting of an evolving lineage happened. Something happened that caused the divergence breaking a population into 2 components and from then on took different trajectories.

Levels of organisation

How evolutionary biologists consider evolution independently. Sequences, molecules, cells, organisms, populations, ecosystems

Phenotype

The sum of an organisms observable characteristics -influenced by genotype + environment

Phenotypic traits

Specific characteristics of an organism determined by genotype interactions with the environment

Fitness

How good a particular genotype is at leaving offspring in the next generation relative to how good other genotypes are at it

Adaptation

A trait of an organism that has evolved over a period of time by process of natural selection.

What does adaptation increase

Expected long-term reproductive success of the organism

Two-scale structure of biodiversity

Every organism belongs to a more or less distinct group of very similar organisms. Leads to 2 distinct scales in evolution of life

Macroevolution

Profound changes at the scale of differences between different forms of life. Describes origin of novel organisms.

Micro evolution

Small changes at the scare of differences between members of the same population

2 definitions of evolution

Changes in species over time and changes in a gene pool over time

Evolution mostly doesn't...

Lead to new species - instead leads to changes within species

Changes in species over time

Often associated with long tine period, slow changes, evidence from fossils - macroevolution

Changes in gene pool over time

Evolution that does not necessarily lead to new species, happens through very small changes in the genome that effect he species- can be rapid - microevolution

Ideas current before Darwin's work

Earth was a few thousand years old, specific creation theory, extinction unknown

When did life on earth arise?

Stromatolites - 3.7 bya

Molecular clock - 4.2 bya

The molecular clock

The idea that genomes are changing at different rates depending on the organism - based on level of mutation you can work out an age difference/time to most recent common ancestor they shared

Carl Linnaeus 1707-1778

Developed binomial system - hierarchal classification based on physical similarity

James Hutton 1726 - 1797

Gradualism - profound change is the cumulative product of a slow but continuous process.

Jean-baptiste lamarke - 1700 s

Heritability of acquired characteristics- the idea that species change with time. what an animal experiences is passed on to the next generation

Georges Cuvier 1769 - 1832

Founder of paeleontology - opposed evolution. Suggested boundaries betweenfossil layers corresponded to catastrophic events. Showed extinction

Charles Lyell - 1797 - 1875

Uniformitarianism: explain former changes of earth's surface by reference to causes still operating today- wrote - the principles of geology

Thomas Malthus 1766 - 1834

Principle of population - exponential population growth relative to resource availability

Darwin finding fossils

Toxin - rat-like creature and giant armadillo-like fossils

Galapagos finches

Showed evidence for adaptation through beaks - used for different food sources. E.g. Insects, cacti, and seeds

Darwin's theory of evolution

All life evolved from a single common ancestor and adaptation is due to natural selection but there may also be other mechanisms of evolution

Problem with Darwins idea

Didn't know about Mendelian genetics and how inheritance worked

Darwins experiment when he returned

Artificial selection with pigeons before Mendelian genetics - selected for behaviour and morphology

Pigeon breeding for behaviour

Tumbler pigeons undergone artificial selection to do backflips when flying for predator evasion

After returning from the beagle

Variation within species being studied - barnacles

Darwin's importance of variation

Only variation that mattered was inherited variation

Observations critical for natural selection

Some related organisms were more similar than unrelated ones or further related ones

How do individuals cope with environmental conditions

Some have traits to survive and can pass these on, others don't

Final goal of evolution

There is he final goal - everything is constantly changing to meet needs of changing environment

Link between Malthusian theory and Darwin

Not every organism in a population reproduces and contributes to the next generation - many die without.it is a competition among and between species for resources and survival of the fittest - Malthus = reproduction outruns resources

Limiting population growth

Most off spring do not survive e.g. oysters - 2 out of 114 million eggs survive. Reproduction outruns resources.

Who lives and who dies out of offspring?

Variation = random, survival = nonrandom. This is 'survival of the fittest'

Significance of fitness

Individuals that are fit and survive leave more offspring, those lineages with fitter offspring survive through evolutionary time.

4 conditions of evolution through natural selection

1. Individuals within a species are variable

2. Variation is heritable

3. Every generation produces more individuals that survive

4. Survival is not random - competition etc.

Who is more likely to survive and increase a population

Those with more favoured forms in variation and better adapted traits

Why did Darwin sit on his idea for 20 years

To collect evidence, shelter from outrage, and strengthen his case

Alfred Russell wallace

1858 - came up with the idea of natural selection and wrote to Darwin asking about publicising his work

Problem in Wallace's idea

Lack of mechanism to explain heredity and how favourable traits are transmitted to later generations - blending model initially assumed

Solution to problem of lack of mechanism

Mendels peas! Particulate inheritance - 'modern synthesis'

Natural selection

Mechanism of evolution that consistently causes adaptive evolution

Adaptation

Any alteration in the structure or function of an organism that results from natural selection and by which the organism becomes better fitted to survive and multiply in its environment.

First key point about natural selection

NS acts on individuals but the population roles

Second key point about natural selection

Natural selection doesn't 'think'!

Third key point about natural selection

NS can't produce perfect adaptations or grant organisms what they 'need'

Fourth key point about natural selection

NS produces new traits by modifying existing traits

Fifth key point about natural selection

Historical constraints mean adaptations aren't perfect - e.g. Disk herniation in humans due to evolution

Sixth key point about natural selection

Adaptations are or can be compromises or trade offs -e.g frogs mating call

Adaptation to climate change

Salmon in Alaska - DNA data shows them migrating from Ocean 2 weeks earlier than 32 years earlier s a result of natural selection favouring fish that migrate earlier

Population genetics

The study of evolutionary mechanism's that lead to changes in allele frequencies of populations from generation to generation - links evolutionary biology with genetics. Looks at how variation changes across generations and among populations.

Population

A localised group of individuals capable of interbreeding and producing fertile offspring.

A population consists of...

Members of one species, but not necessarily all the members of that species - one species may have many populations, locally or internationally.

Fixed locus

If all individuals in a population are homozygous for the same allele

Polymorphic locus

When there is more than one allele at a locus

Gene pool

All of the alleles for all loci in a population

Locus/loci

Spot on a chromosome where an allele is located

Potential fates of an allele as a result of mutation

Lost, increase in frequency, fixed.

Key concepts in population genetics

Variation, how variation changes over time, geographic distribution of variation in space

Dynamics of variation over time

Drift (neutral alleles) and in small populations natural selection (functional alleles)

Geographic distribution of variation in space

Allele frequencies changing through migration - gene flow

The big 4 mechanisms of evolution

Mutation, genetic drift, NS, gene flow

Mutation

Changes allele frequencies

Genetic drift

Random fluctuations in allele frequencies greater in small populations than in large populations

Natural selection

Different survival and reproductive success of individuals with different genotypes changes allele frequencies

Gene flow

Transfer of alleles between populations changes allele frequencies

Allele frequency

The frequency of any given allele in a population, relative to all the other alleles at the same locus.

Equation for allele frequency

Allele frequency = number of copies of a particular allele in a population/ total number of all alleles for that gene in a population

Hardy - Weinberg equilibrium

Allele and genotype frequencies will remain constant from generation to generationin the absence of evolutionary influences - 'big 4'

4 mechanisms of evolution

Mutation, genetic drift, gene flow natural selection

Rarity of mutation

1 in every 100,000 genes / generation

Most mutations occur in

Somatic cells - only genetic can be passed down

Genetic drift describes

How allele frequencies fluctuate unpredictably from 1 generation to the next

Genetic drift tends to reduce...

Variation through loss of alleles ( good or bad)

How can drift change allele frequencies

Random chance events lead to fluctuations in which alleles are passed on and which are lost based on survival and reproduction - can become fixed , more or less common, or lost entirely.

Fixed allele

Present in all individuals

Why is genetic drift felt more in small populations

Smaller gene pool = less variation, so lower ability to respond to what gets thrown at it

Bottleneck effect

When a small surviving population after a random event passes their alleles to the next generation

Example of bottle neck effect

Panthers in Florida - conservationists tried to bring in panthers from elsewhere to rebuild population and reestablish. Variation so they could still maintain role in ecosystem

The founder effect

When a few individuals become isolated from a larger population and by chance- allele frequencies in smaller population car be different from those in the larger population

Example of founder effect

Amish people - from Germany to USA, 2 people carried recessive allele for 12 fingers. Rare trait to have los recessive, but since such a small community, trait common as more carriers of allele/genotype have babies together

Natural selection increases...

Frequency of alleles that enhance survival + reproduction and adaptive evolution occurs as the match between an organism and it's environment increases

Quantitative traits

Traits controlled by many genes