Evolution Evolution

Evolution and the Theory of Evolution and the Theory of Natural Selection Natural Selection

Developing a Theory of EvolutionDeveloping a Theory of Evolution

• Evolution is undeniable. Evolutionary theory is a collection of carefully reasoned and tested hypotheses about how evolutionary change occurs.

• Today’s physicists don’t completely understand gravity, but it exists.

Influences on Darwin’s Influences on Darwin’s IdeasIdeas

Jean Baptiste de LamarckJean Baptiste de Lamarck

• (1744-1829) – one of the first to recognize that living things changed over time.

3 assumptions:3 assumptions:

• Organisms had an inborn urge to better themselves

• Change occurred because organisms could alter their shape based on their needs.

• by trying to fly, birds grew wings.• Organisms could pass on acquired traits from

generation to generation• Remember: Lamarck did not understand

genetics

Theory of “Use vs. Disuse”Theory of “Use vs. Disuse”• Similarly, the big,

“ripped” muscles developed by the village blacksmith with all his hammering and slinging of heavy metal objects would be expected to be passed on to his offspring.

• The long necks of giraffes were due to their stretching for food, and giraffes passed their stretched necks on to their offspring.

Charles LyellCharles Lyell

• Lyell demonstrated the earth was very old (4.6 billion years)

Charles LyellCharles Lyell

• Without that information, Darwin’s theory could not work – it would have taken long periods of time to evolve millions of species.

• Darwin witnessed changes in earth geography – volcanoes, earthquakes – if the earth can change, so, too could life on the earth

Farmer’s influence:Farmer’s influence:

• Darwin spoke to plant and animal breeders

• Breeders altered and improved crops and livestock

• Darwin wanted to know how these breeding programs work?

Farmer’s influence:Farmer’s influence:

• Farmers could not cause variation to occur, it happened or it did not.

• If variation occurred, the farmers could take advantage of it.

• Breeding cows that gave most milk, or other desirable characteristics – artificial selection

• Darwin believed that nature must have a similar process – only allowing the organisms best suited to their environment to survive – Natural Selection

Malthus: Population ControlsMalthus: Population Controls

• Thomas Malthus was an Economist

• observed that babies were being born at a faster rate than people were dying

• Sooner or later, not enough food or resources

Malthus: Population ControlsMalthus: Population Controls

• Darwin realized that this applied to animals even more than people. Most animals made more offspring

• Most baby organisms die, and very few survive to raise their own offspring

• What allows them to survive and raise offspring? Fitness

Darwin made some profound Darwin made some profound observations, from which he inferred observations, from which he inferred

some brilliant conclusions...some brilliant conclusions...

• Observation #1. All species have huge potential fertility

• Observation #2. Except for seasonal fluctuations, populations tend to maintain a stable size.

• Observation #3. Environmental resources are limited.

Natural SelectionNatural Selection

The Four Basic IdeasThe Four Basic Ideas

Natural SelectionNatural Selection

1. Organisms are capable of producing huge numbers of offspring.

2. Those offspring are variable in appearance and function, and some of those variations are heritable.

3. Environmental resources are limited, and those varied offspring must compete for their share.

4. Survival and reproduction of the varied offspring is not random. Those individuals whose inherited characteristics make them better able to compete for resources will live longer and leave more offspring than those not as able to compete for those limited resources.

Genetics and Evolutionary TheoryGenetics and Evolutionary Theory

• Peppered moths

• Verified by HBD Kettlewell experiment

• Darwin did not have the benefit of understanding of genetics

Genetic VariationGenetic Variation

• Genes are the sources of random variation

• Genetic variation does not occur because an organism wants it to (as Lamarck suggests)

• All members of a population (group of individuals of the same species) share a common group of genes – the gene pool.

SpeciesSpecies

• Species is a group of similar-looking (though not identical) organisms that breed with one another and produce fertile offspring in the natural environment.

• Speciation

• Speciation is a process of organisms evolving into new species

NicheNiche

• A combination of where an organisms lives and what functions it performs are called its niche

• No 2 species can occupy the same niche in the same location for a long period of time.

Reproductive IsolationReproductive Isolation

• Scientists have learned that new species usually form only when populations are isolated, or separated

• Species that are separated so they do not interbreed is called reproductive isolation

• Gene pools become dissimilar

• A population becomes physically separated from the rest of the species by a geographical barrier that prevents interbreeding. 

• Because gene flow is disrupted by this physical barrier, new species will form.

Allopatric SpeciationAllopatric Speciation

• Two populations are geographically close to each other, but they are reproductively isolated from each other by different habitats, mating seasons, etc.

Sympatric SpeciationSympatric Speciation

Finches of GalapagosFinches of Galapagos

• Darwin observed finches on the Galapagos Islands

• 14 different finches – evolved from a common ancestor

• All have body structures and behaviors that allow them to live in different niches

Finch Finch Feeding StylesFeeding Styles

• Some feed on small seeds

• Some crack open larger seeds

• Some pick ticks from reptiles

• Some use twigs to get insects out of dead wood

• Vampire finches – drink blood of seabirds

What may have happened?What may have happened?

1. Founding fathers and mothers – ancestral finches found the Galopagos Islands (finches do not like to fly over water for any distance) – They may have gotten lost, or blown off course etc.

2. Separation of populations – Some birds from one island (A) crossed to another island (B).

3. Changes in the Gene Pool - Over time, each population adapted to the needs of their environment

What may have happened?What may have happened?

4. Reproductive isolation – Birds from A cross to B. Will they be able to breed with birds from B? Probably not. Beak size, shape whatever.

5. Sharing the island – 3 possibilities – – Coexistence – would need different niches– Extinction – competition with one better suited

than the other for that niche– Further Evolution - if one exhibits enough

genetic variation, competition will cause further evolution.

Adaptive RadiationAdaptive Radiation

• The process of one species giving rise to many species is called adaptive radiation or divergent evolution

Convergent evolutionConvergent evolution

• A phenomenon in which adaptive radiation among different organisms causes different species that have similar appearance and behavior – example – fish pectoral fins, dolphin fins

Analogous structuresAnalogous structures

• structures with similar function and appearance but from different organisms

Genetic DriftGenetic Drift

• We now know that gene pools can change, even without natural selection – this is Genetic Drift.

• If an individual produces more offspring than others of the species – by chance

• Usually occurs in small populations *• Environmental events can wipe out many

individuals that do not carry a particular allele – that allele becomes more prevalent

All characteristics do not have to All characteristics do not have to contribute to “Fitness”contribute to “Fitness”

• Rhinoceros’ – African – two horns, Indian – 1 horn

• Horns are an advantage, but number of horns doesn’t make a large difference

Stabilizing SelectionStabilizing Selection

• All species do not change all of the time

• Stabilizing Selection – when organisms are well suited to their environment and natural selection does not favor changes – example: shark, Limulus, turtles, ferns

Pace of EvolutionPace of Evolution

• some scientists say speciation is the eventual outcome of gradually accumulating changes of ancestral species – this is called Gradualism (trouble is – fossil records are incomplete)

• Mass Extinction - the result of dramatic change in environment that results in many species vanishing

• Recently findings indicate that a species lived for long periods then “suddenly” (million years) a new set of different, but related organisms took their place for a long time – Punctuated equilibrium

Hardy-WeinbergHardy-Weinberg

• HW law states --> original of a genotypes alleles remains CONSTANT

• HW Equilibrium... is defined algebraically any gene with 2 allelic forms... A and a• let frequency of one allele (A) = p & frequency of other allele

(a) = q

• then by definition, p + q = 1

• HW equation... (p + q)2 = p2 + 2 pq + q2 = 1

• GG Gg gg

Hardy-WeinbergHardy-Weinberg

• What are the H-W frequencies for the following population of plants with different colored flowers?

• 63 red (RR), 294 pink (Rr) and 343 white (rr) = 700 plants, 1400 genes or alleles

• Is the population in H-W equilibrium?

Anthropological EvolutionAnthropological Evolution

• The history of hominids (Present day & extinct)

PhylogenyPhylogeny

• The history of hominid life depicted as a branching tree

• Earliest hominids are placed at the trunk

• Each branch represents a new species which inherits many traits from the ancestor but also has a new trait which appear for the 1st time

Phylogenetic TreePhylogenetic Tree