Theories of Evolution

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Species

A biological group of organisms that resemble each other (variation and sexual dimorphism can exist), able to reproduce w/ each other and produce a fertile offspring

Larmarck’s Theory

“Larmarckism” by Lamarck

1. The use and disuse of organs

2. Inheritence of acquired traits

The use and disuse of organs (Lamarckism)

Organism respond to changes in their environment by developing new organs or developing structure and function of pre-exisiting ones.

“use” in Lamarckism

An adaption to the environment; the new organ is an acquired trait

“disuse” in Lamarckism

Reponse to environmental change by which organ disappears because no longer needed

Lamarck believed that …

Organs that were used regularly became stronger and developed and organs that were not used simply withered away.

Inheritence of acquired traits

Acquired traits were passed on to offsprings, that offsprings benefit from useful structures developed by their parents.

Lamarck’s famous example

Early giraffes maybe short necks (eat grass), if grass scarce have to stretch neck to eat leaves in trees. More stretch = longer neck. Passed onto offsprings. Organism change as environment change.

Why Lamarck’s ideas are invalid

A “will” to better an organism (stretching neck because giraffe “want” to reach high in tree) is vague and weak argument.

Lack of evidence 4 acquired traits. Other cases concept doesn’t work. Cut dogs tail but no puppy born with short tail.

Genetic view, no change in genetic material. Also only mutation in gametes are passed on.

Lamarck’s hypothesis for evolution is …

no longer accepted

Larmarck offered …

an explanation for mechanism of evolution. That species change over time and that environment is a factor, that evolution is adaptive and diversity of life is result of adaptation.

Darwin’s Theory (“Darwinism”)

Charles Darwin published Origin of Species by Natural Selection in 1859.

Showed that all living things evolved from other living things.

The voyage of the HMS Beagle

Darwin joined the crew (as captain companion → chief naturalist) of the HMS Beagle that set sail for a five year mapping and collecting expedition to South America and South Sea islands.

In the beginning of the voyage Darwin …

did not accept that species changed. He believed the Earth was about 6000 yo and remained same except effects of floods and other catastrophes, that organisms were designed by a “Creator” for certain habitats.

Early in the voyage …

Darwin began to change his ideas.

Read works of a noted geologist and saw evidence that Earth was very old.

Realized that mountains could be built by the action of earthquakes over millions of years.

Found fossils of marine animals in high mountains and realized the rocks must have been lifted out of the ocean.

Darwin while exploring …

The Galapagos islands observed 14 species of finches similar to finches found on mainland. Difference lay in shape of their beaks and each suited for obtaining a certain kind of food.

Darwin also saw …

examples that indicate animals in similar environments did not always look alike.

ex. emus (Australia) and rheas (South America) two unrelated species and occupy same kind of habitat.

→ If animals formed for special habitat, why would different species be found in similar habitats?

When Darwin returned to England he was …

convinced that all living things arose by evolution. Next 23 years, he would gather evidence for his theory. book published in 1859.

Critical elements of Darwin’s theory

1. Population tend to produce more than evironment can support

2. Struggle for existance

3. Variation exists within species

4. Environment selects organisms with the best traits

5. Adaptation

Populations tend to produce more offsprings than the environment can support

Living things in an enviroment die before they reproduce.

→ Because natural resources are limited, environment cannot support, and organisms eaten as food, killed by non living and living factors.

Struggle for existance

Consequence of overproduction.

All organisms compete for limited natural resources. Some will get more and some less.

Variation exists within species

Members of a species vary in physical characteristics (traits), physical variations can be passed from generation to generation

Environment selects organisms with the best traits

Natural selection = Organisms better suited to environment survive and reproduce (pass trait to offspring) at a greater rate than organisms less suited to the environment.

Acts to select “fit” individuals

Natural selection cont.

The major governing force of evolution.

Environment change = traits selected change

Lead to descendants so different become new species

Fitness

Measured by the number of fertile offspring produced.

Adaptation

Natural selection causes populations and species to become adapted to the environment.

• Slow

• Each subsequent generations more individuals better adapted.

Darwin believed the process of evolution occurred as a result of …

selection of traints (natural selection) by constant environmental changes (wind, flood, heat, cold, etc)

Peppered moth story

In Manchester UK has two variants of peppered moth: one dark and other light (inherited)

Before Industrial Revolution, more light moth than dark moth. Habitat light coloured trees, light moth camouflaged better eaten less reproduce more dark moth opposite.

During and after Industrial Revolution, soot turn trees dark light colour moth situation is flipped (less light moth more dark moth same reason as above)

Recent & current, pollution control, trees → light = light moth increasing.

Evolution acts on …

Populations, not individuals

Population

A group of organism of the same species living in the same area and can interbreed.

Certain traits help define a population

1. Anatomical Traits

   = members have overall same form and appearance

2. Physiological Traits

   = cells and body parts of all individual in population work same (growth, everyday tasks, and reproduction)

3. Behavioral Traits

   = Individuals of a population generally respond the same to basic stimuli e.g. human babies instinctively imitate facial expressions

Genes

Heritable factor that controls a specific characteristic, consisting of a length of DNA occupying a locus

Locus

A position on a chromosome

Gene pool

All the genes in the entire population, in theory is avaliable to all of its reproducing members.

Alleles

Two or more slightly different forms of a kind of gene.

Genotype

A set of alleles inherted by an individual

Homozygous dominant and recessive

Both alleles for a trait are the same.

Dominant when both alleles are dominant EE

Recessive when both alleles are recessive ee

Heterozygous

two alleles for a particular characteristic is different from each other.

Dominant allele

Always shows

Recessive allele

Only show when on its own (sex chromosome) or when both alleles are same (homozygous)

Phenotype

Genotype codes for phenotype

The differences in morphological, physiological, and behavioral traits from one individual to the next.

E.g. free “dangling” earlobe EE or Ee, attached earlobe ee

Homologous pairs

Each homologue (one maternal other paternal) carries an identical assortment of genes (4 a trait e.g. eye color), but the allele (blue eyes, brown eyes, etc) of the gene from each parent may differ.

Five factors that affect combination of alleles

1. Gene mutation (produces new alleles)

2. Crossing over prophase I (new combinations of alleles in chromosomes recombinant chromosomes)

3. Independent assortment metaphase I (mixes maternal and paternal chromosomes in gametes)

4. Random fertilization (put together combinations of alleles from two parents)

5. Chromosome mutation (lead to loss, duplication, alteration of alleles)

Of the factors … the only

A gene mutation source of NEW variation. It alone create alleles.

Allelic frequencies

The # of times an allele occurs in a gene pool compared with the # of times other alleles for the same gene occurs

Allelic frequency of an allele increase or decrease if …

Allele increases the chances of survival and reproduction of the individuals that possess it. Vice versa for decrease.

Microevolution

Small-scale change in frequency of alleles within a single population over a number of generations.

Macroevolution

Occurrence of large-scale changes in gene frequencies in a population over a geological time period (consisting of extended microevolution) tells how species or higher levels of classification are related to one another.

Difference btwn microevolution and macroevolution

Microevolution happens on a small scale (within a single population), while marcoevolution happens on a scale that transcends the boundaries of a single species.

Both level of evolution relies on …

The same established mechanisms of evolutionary change.

Four major factors that alter allele frequencies and …

Brings about the most evolutionary change are:

1. Natural Selection

2. Gene Flow

3. Genetic Drift

4. Mutations

Natural Selection (Allelic frequency)

Impacts the reproduction of genotypes within a population, major force in changing frequency of alleles.

Results in alleles being passed to next generations in proportions different from their relative present frequencies.

Natural selection is selecting for the fittest phenotype that then affects the genotype.

Gene Flow

Frequency of alleles may change due to migration of organisms (in = immigration out = emigration) of a population.

Organisms that enter/leave a population take gene in/out of the gene pool.

Genetic Drift

Allelic frequency may change by pure chance. Significant in small populations only.

Happen due to inability to locate a mate, population small (not enough mates) or due to a catastrophe (those who survive do by chance not due to a advantage)

Two situations increase impact of genetic drift

The bottleneck effect and the founder effect

The bottleneck effect

Genetic drift resulting from the drastic reduction of a population (natural disaster) such that surviving gene pool is not genetically represenative of original population’s gene pool.

By chance certain alleles may be overrepresented, underpresented, and eliminated (wiped) among the survivors.

Reduce genetic variation.

The founder effect

Genetic drift that occurs when a few individuals (“founders”) become isolated from a larger population, results in new population’s gene pool not reflective of original population’s gene pool.

Account for relatively high frequency of certain inherited disorders among isolated human populations. (Polydactyly more common in Amish communities)

Mutations

Most harmful, mutant organism may be less fit than normal organism. Mutant gene removed from gene pool if mutant organism fails to reproduce. Some beneficial, mutant more adapted (environment) and fit pass gene to offspring.

Do not have immediate evolutionary effect, provide a source of variation in gene pool (can be influenced by natural selection). Heritable changes serve as raw material of evolution.

In sense of the definition of species. Species is the …

biggest gene pool possible under natural conditions. Meaning individuals in the same species share a common gene pool.

All breeds of domestic dogs, cats, cows, horses, etc …

are the same species.

What must happen for a species to evolve into two new species?

The gene pools of two populations must be seperated or isolated for them to become a new species.

Reproductive isolation

The seperation of populations so that they do not interbreed. If not two populations gene pools will blend with each other. No new species formed. Agent for formation of new species.

When reproductive isolation occurs …

natural selection usually increase diff. btwn seperated populations.

As populations become better adapted to diff. environ.

Their seperate gene pools gradually become more dissimilar.

If the populations remain seperated for long period of time …

their genes pool become so diff. reproductive isolation becomes permanent (groups of organisms no longer sep. population, now seperate species)

Causes of reproductive isolation

1. Geographic isolation

2. Behavioral isolation

3. Temporal isolation

Geographic isolation

Occurs when two populations are seperated by geographic barriers (rivers, mountains, altitude, deserts, ice sheets, other bodies of water)

Behavioral isolation

Occurs when two populations are capable of interbreeding but have differences in courtschip rituals (calls, dances, body language) or oth. reproductive strat. (pheromones - chemical signals) that require it. So they will not mate with each other.

Temporal isolation

Occurs when two or more species reproduce at different times. E.g. pigeons reproduce in morning, owls reproduce at night.

Speciation

lineage-spltting event that produces more seperate species. Is the branching point in trees of life.

Darwin’s finches

A group of 14 bird species on the Galapagos, helped form Darwin’s theory of natural selection. All evolved from a single ancestral species. Yet exhibits body structures and behaviors that enable it to live in a diff. niche.

Speciation of the ancestor finch steps

1. Founding fathers and mothers arrive

2. Geographic isolation

3. Changes in the gene pools

4. Reproductive isolation

5. Ecological competition

Founding fathers and mothers arrive

A few finches from the South American mainland blown or flew to one of the Galapagos islands. Once arrived they managed to survive and reproduce.

Geographic isolation

Later, some birds from species A crossed to another island, now finch populations on two islands isolated from each other and no share common gene pool.

Changes in the gene pools

Over time, populations on each island adapated to their local environments. On one island plants produced larger thick shelled seeds. Natural selection would select for individuals w/ larger beaks to crack hard seeds easily. They survive and reproduce then over time that population evolved larger beaks, forming population B.

Reproductive isolation

If birds from population B with large beaks cross to island of birds with small beaks for small seeds. The two populations will prob. not breed with each other due to behavioral isolation (finches prefer to mate with birds that have same size beak as them). Only breed within their own population, they have become seperate species.

Divergent evolution

A single species or a small group of species (common ancestor) has evolved, through natural selection and other processes, into diverse forms that live in different ways.

Also known as adaptation or adaptive evolution

Evidence for divergent evolution

Homologous structures (homologies) are evidence of past (but recent can’t be too distant) divergent evolutions. Body parts (same anatomy) of related organims evolved to perform different functions. Meaning that they have a shared common ancestor.

Convergent evolution

Unrelated organism can become adapted to a similar environment or niches and develop characteristics that are more or less similar to one another.

Example of convergent evolution

Stream-lined body shape and flippers of many different animals.

Evidence for convergent evolution

Convergent evolution produced many analogous structures (analogies) in modern organisms. They are similar in appearance and function, but have diff. origins, so they usually have very diff. anatomy.

Example of analogous structures

Moth wing VS bat wing or bird wing.

Compare and contrast homologies and analogies

Homologies are traits that different lineages inherited from their recent common ancestor. Evidence for divergent evolution.

Analogies are similar traits that were not inherited from a common ancestor but evolved separately. From two unrelated lineages adapting to similar environment. Evidence for convergent evolution.

The “wings” of sugar gliders and flying squirrels are …

analogous because they’re very distantly related, highly unlikely their common ancestor had “wings” and that both modern animals inherited the trait from this animal. Instead each lineage probably evolved the trait independently (convergent evolution).

The rate of evolution

gradualism and punctuated equilibrium are two ways evolution of a species can occur. A species can evolve by only one of these or both. Shorter mostly punctuated equilibrium and longer evolution mostly by gradualism.

Gradualism

Rate of evolution was very slow and it took millions of years of slow, gradual, constant changes to bring about evolution of a new species. If species evolve by gradualism, there should be transitional forms seen in the fossil record.

Punctuated equilibrium info

Fossils of some species remained virtually unchanged over million of years (conflicts with gradualism). And some organisms seem to have appeared out of nowhere and suddenly in the fossil record, and changing rapidly.

Punctuated equilibrium

Concept that evolution takes place in spurts of rapid change, followed by “stasis” long periods of little or no evolutionary change.

Punctuated equilibrium, can occur when …

crucial factor in environment changes (e.g. harsher weather) and occur due to sudden dramatic mutation which gives organism major advantage brings about burst of change that quickly creates a new species.

The species change …

very rapidly over a few generations, then settle down again to a period of little change (stasis)

Evolution of stripes tiger using gradualism

Long time back, alot of tiger like animals without strips. A few had light markings and color variation. They were more fit (hunted better, survived, and reproduce) than unmarked. In next generation more animals marked. Variation of # of marks and mark defintion (clear or faint) existed in marked animals. Again marked fitness > no marked, and better marks (clear and more) fitness > worse marks (faint and less). Very gradually, over a lot of generations stripes over tiger’s whole bodies formed in the entire population.

Evolution of stripes tiger using punctuated equilibrium

Long time ago, a lot of tiger-like animals without stripes. One time, a mutation occured in a few of the animals that gave offsprings stripes. Made those and offsprings with stripes so fit (little or none died and reproduce). Over a few generations the whole population was born stripped.

Evolution of tiger stripes using both grad. & punc.

A mutation had a huge effect, causing distinct, stripes-like markings in offsprings. These were gradually “polished up” into stripes.

Mass extinction

Many species going extinct, happens every now and then. Five major extinction events in the history of life on Earth and a sixth extinction is now in effect.

More than …

99 percent of all species that have ever lived are now extinct.

One hypothesis suggests that at the …

end of the Cretaceous Period, a huge asteroid wiped out the dinosaurs and many other organisms. The impact threw huge amounts of dust and water vapour into the atmosphere and probably caused an ice age (that played a role in dinosaurs end). (Single major cause)

However paleontologists think that …

most masss extinctions were caused by several factors. During several mass extinctions many large volcanoes were erupting, continents were moving, and sea levels were changing.

Effects of mass extinction

Extinction of many species left habitats open and provide ecological opportunities for those organism that survived. Those that remain find lots of empty habitat.

Groups of organisms with …

enough genetic variability can undergo convergent and divergent evolution, that produce a burst of many new species to fill empty habitats. Extinction of “dinosaur'“ cleared way for the evolution of modern mammals and birds.