EVOLUTION. The Unifying Concept b “Nothing in biology makes sense, except in the light of evolution.” Theodosius DobzhanskyTheodosius Dobzhansky b Evolution:

EVOLUTIONEVOLUTION

The Unifying ConceptThe Unifying Concept

““Nothing in biology makes sense, Nothing in biology makes sense, except in the light of evolution.”except in the light of evolution.”• Theodosius Dobzhansky Theodosius Dobzhansky

Evolution: The descent of modern Evolution: The descent of modern organisms with modification from pre-organisms with modification from pre-existing life-forms; strictly speaking, existing life-forms; strictly speaking, any change in the proportions of any change in the proportions of different genotypes in a population different genotypes in a population from one generation to the nextfrom one generation to the next

All Life Shares a Common All Life Shares a Common AncestryAncestry

Are the these organisms...

…related?

YES!!!YES!!!

How can that be? They are so very How can that be? They are so very different.different.

But they share at least seven But they share at least seven characteristics…right?characteristics…right?

So, if all organisms have an unbroken So, if all organisms have an unbroken chain of ancestors leading back to the chain of ancestors leading back to the first of its kind, then each of those first of its kind, then each of those ancestors must have its own chain of ancestors must have its own chain of ancestorsancestors

EXAMPLEEXAMPLE

Some distant ancestor of today’s Some distant ancestor of today’s elephants is also the ancestor of elephants is also the ancestor of the extinct mammothsthe extinct mammoths

If we follow this line back far If we follow this line back far enough, it links up with other enough, it links up with other ancestors of other organisms which ancestors of other organisms which ultimately links up with the HUGE ultimately links up with the HUGE tree of life, linking ALL organismstree of life, linking ALL organisms

Chuck D!!!Chuck D!!!

We can’t discuss evolution without We can’t discuss evolution without mentioning Charles Darwin mentioning Charles Darwin

His pivotal idea that all organisms are His pivotal idea that all organisms are the result of descent with modification the result of descent with modification from common ancestors is the from common ancestors is the foundation of evolution and a bedrock foundation of evolution and a bedrock principle of biologyprinciple of biology

He also delivered a theory for the cause He also delivered a theory for the cause of evolution: natural selectionof evolution: natural selection

Sooooo…...Sooooo…...

Thanks Chuck!Thanks Chuck!

Oh yeah, what about Oh yeah, what about Wallace?Wallace?

Who?Who? Wallace... Alfred Russell WallaceWallace... Alfred Russell Wallace He devised the same theory that He devised the same theory that

Darwin did but he didn’t know Darwin did but he didn’t know enough big wigs so they wouldn’t enough big wigs so they wouldn’t publish his work until after Darwin publish his work until after Darwin published his…and he sat on it for published his…and he sat on it for a few yearsa few years

Let’s Summarize Their Let’s Summarize Their TheoriesTheories

Observation 1.Observation 1.• Natural populations have the potential to Natural populations have the potential to

increase rapidly because organisms can increase rapidly because organisms can produce far more offspring than are produce far more offspring than are required to replace their parentsrequired to replace their parents

Observation 2.Observation 2.• Nevertheless, the sizes of most natural Nevertheless, the sizes of most natural

populations and the resources available to populations and the resources available to maintain them remain relatively constant maintain them remain relatively constant over timeover time

ConclusionConclusion

There is competition for survival There is competition for survival and reproduction. In each and reproduction. In each generation, many individuals must generation, many individuals must die young, fail to reproduce, die young, fail to reproduce, produce few offspring, or produce produce few offspring, or produce less fit offspring that fail to survive less fit offspring that fail to survive and reproduce in their turnand reproduce in their turn

Observation 3Observation 3

Individual members of a population Individual members of a population differ from each other in their differ from each other in their abilities to obtain resources, abilities to obtain resources, escape predators and survive escape predators and survive change in their environmentschange in their environments

Conclusion 2Conclusion 2

The most well-adapted individuals The most well-adapted individuals in any generation tend to be the in any generation tend to be the ones that leave the most offspringones that leave the most offspring

Observation 4Observation 4

At least some of the variation At least some of the variation among individuals, in traits among individuals, in traits necessary for survival or necessary for survival or reproduction, is due to genetic reproduction, is due to genetic differences that may be passed on differences that may be passed on from parent to offspring from parent to offspring (don’t (don’t forget, genotype controls phenotype)forget, genotype controls phenotype)

Conclusion 3Conclusion 3

Over many generations, Over many generations, differential or unequal, differential or unequal, reproduction among individuals reproduction among individuals with different genetic makeup with different genetic makeup changes the overall genetic changes the overall genetic composition of the populationcomposition of the population

How do we know evolution How do we know evolution has occurred?has occurred?

What do you think?What do you think? Fossil record, comparative Fossil record, comparative

anatomy, embryology, anatomy, embryology, biochemistry, and geneticsbiochemistry, and genetics

The Fossil RecordThe Fossil Record

The fossil record shows a slow The fossil record shows a slow change over timechange over time

We see a progressive series of We see a progressive series of fossils leading from an ancient, fossils leading from an ancient, primitive form, through primitive form, through intermediate stages culminating in intermediate stages culminating in the modern formthe modern form

The best example we haveThe best example we have

The fossil record of the horse is the The fossil record of the horse is the best example of thisbest example of this

That of elephants, giraffes and That of elephants, giraffes and mollusks are good as wellmollusks are good as well

They all suggest that species They all suggest that species evolved from and replaced evolved from and replaced previous speciesprevious species

Comparative anatomyComparative anatomy

Appearance has long been used as Appearance has long been used as an indicator of the relatedness of an indicator of the relatedness of organismsorganisms

The elephant and the mammoth The elephant and the mammoth clearly have similar anatomies and clearly have similar anatomies and share a common ancestorshare a common ancestor

Unrelated species in similar Unrelated species in similar environments…environments…

……have evolved similar formshave evolved similar forms Natural selection predicts that unrelated Natural selection predicts that unrelated

species, given similar environmental species, given similar environmental demands, independently evolve demands, independently evolve superficially similar structures. This is superficially similar structures. This is called called convergent evolutionconvergent evolution..

Outwardly similar structures in Outwardly similar structures in unrelated organisms are termed unrelated organisms are termed analogous structuresanalogous structures

Examples of convergent Examples of convergent evolution and analogous evolution and analogous structuresstructures

What about related What about related organisms?organisms?

Modern organisms are adapted to a Modern organisms are adapted to a wide variety of habitats and lifestyleswide variety of habitats and lifestyles

The forelimbs of birds and mammals, The forelimbs of birds and mammals, for example, are variously used for for example, are variously used for flying, swimming, running (over several flying, swimming, running (over several different types of terrain), and graspingdifferent types of terrain), and grasping

Despite this diversity of function, the Despite this diversity of function, the internal anatomy is remarkably similarinternal anatomy is remarkably similar

These internally similar structures are These internally similar structures are called called homologous structureshomologous structures

Examples of homologous Examples of homologous structuresstructures

Figure 3.1.1. Comparison of the forelimbs of various relatives of modern birds. Forelimbs of (A) Ornitholestes, a theropod dinosaur, (B) Archaeopteryx, (C) Sinornis, an archaic bird from the lower Cretaceous,

and (D) the wing of a modern chicken (modified from Carroll 1988, p. 340;

Vestigial structuresVestigial structures

These are structures that serve NO These are structures that serve NO apparent purposeapparent purpose

examples include: molar teeth in examples include: molar teeth in vampire bats, pelvic bones in vampire bats, pelvic bones in whales and snakes, the appendix, whales and snakes, the appendix, wings on antswings on ants

EmbryologyEmbryology

It was observed, in the 1800’s, that It was observed, in the 1800’s, that vertebrate embryos look quite similar to vertebrate embryos look quite similar to each other in early developmenteach other in early development

All vertebrates have gill slits at some point All vertebrates have gill slits at some point in their development. Only fish retain them in their development. Only fish retain them in adulthoodin adulthood

The plausible explanation is that early forms The plausible explanation is that early forms had these traits and passed the genes on had these traits and passed the genes on but in some forms the genes get masked or but in some forms the genes get masked or turned off during developmentturned off during development

HomeworkHomework

Read 255-269Read 255-269 do do applying conceptsapplying concepts 1-6 1-6 do do key termskey terms pg 270 pg 270

Eeewwwww, where are Eeewwwww, where are your lysosomes?your lysosomes?

Biochemistry and geneticsBiochemistry and genetics

These two fields reveal striking These two fields reveal striking evidence for the evolutionary evidence for the evolutionary relatedness of all organismsrelatedness of all organisms

At the most fundamental levels, At the most fundamental levels, ALL living cells are very similarALL living cells are very similar

ExamplesExamples

ALL use DNA as the carrier of genetic ALL use DNA as the carrier of genetic informationinformation

ALL use RNA, ribosomes and ALL use RNA, ribosomes and approximately the same genetic code to approximately the same genetic code to translate genetic information into proteinstranslate genetic information into proteins

ALL use the same 20 amino acids to build ALL use the same 20 amino acids to build proteinsproteins

ALL use ATP as the intracellular energy ALL use ATP as the intracellular energy carriercarrier

Some evidence that Some evidence that populations evolve by populations evolve by natural selectionnatural selection

Artificial Selection: The breeding of Artificial Selection: The breeding of domestic plant and animal species to domestic plant and animal species to produce specific, desirable featuresproduce specific, desirable features

The reasoning is this, if humans can The reasoning is this, if humans can produce such a wide variety of, say, dog produce such a wide variety of, say, dog breeds in a few hundred or thousand breeds in a few hundred or thousand years. years.

It stands to reason that nature could It stands to reason that nature could produce a wide variety of organisms in produce a wide variety of organisms in several several billion yearsbillion years

Natural Selection is Natural Selection is Occurring RIGHT NOW!!!Occurring RIGHT NOW!!!

Evolution did NOT ONLY happen in Evolution did NOT ONLY happen in the pastthe past

There is still competition for space, There is still competition for space, resources and mating right nowresources and mating right now

We already discussed the palmerus We already discussed the palmerus longus tendonlongus tendon

The classic example is the peppered The classic example is the peppered moths (Biston betularia) of Englandmoths (Biston betularia) of England

The Peppered MothThe Peppered Moth

Before the Industrial Revolution most Before the Industrial Revolution most peppered moths were white with peppered moths were white with scattered specks of black pigmentscattered specks of black pigment

They blended in very well with the lichen They blended in very well with the lichen that grew on the sides of trees that grew on the sides of trees

This camouflage was helpful in This camouflage was helpful in preventing predation by birdspreventing predation by birds

There were, however, mutant all black There were, however, mutant all black individualsindividuals

The mutants...The mutants...

……were easily seen against the lichen and were were easily seen against the lichen and were eaten by predatorseaten by predators

During the Industrial Revolution, industries in During the Industrial Revolution, industries in England burned lots of coalEngland burned lots of coal

pollution from the smokestacks covered the lichen pollution from the smokestacks covered the lichen causing it to die off and left the trees covered in causing it to die off and left the trees covered in black sootblack soot

This led to heavier predation of the light colored This led to heavier predation of the light colored moths and there was an increase in the dark moth moths and there was an increase in the dark moth populationpopulation

By the end of the 19th century, 98% of the peppered By the end of the 19th century, 98% of the peppered moths were blackmoths were black

1 more example1 more example

In the 1990’s in Florida a rare mutation in In the 1990’s in Florida a rare mutation in cockroaches was an agent of natural cockroaches was an agent of natural selectionselection

The mutation caused the roaches to dislike The mutation caused the roaches to dislike glucoseglucose

glucose was used as bait in roach poisonglucose was used as bait in roach poison the individuals with the mutation did not eat the individuals with the mutation did not eat

the poison, the ones that did diedthe poison, the ones that did died now the once rare mutation is part of the now the once rare mutation is part of the

widespread genome of that roach populationwidespread genome of that roach population

Three points to Three points to understandunderstand

1. Mutations arise spontaneously1. Mutations arise spontaneously 2. Selection does not necessarily produce 2. Selection does not necessarily produce

well-adapted species. In some cases it well-adapted species. In some cases it causes extinctioncauses extinction• other moth species in England went extinct other moth species in England went extinct

because there was no mutation to cause a because there was no mutation to cause a black variantblack variant

Natural Selection selects for organisms Natural Selection selects for organisms that are best adapted to a particular that are best adapted to a particular environmentenvironment