Evolution Notes

Evolution – the process by which modern organisms have descended from ancient organisms

Charles Darwin (1809-1882) – Englishman cruised around the world on the HMS Beagle

                                                  Discovered the diversity of  life on Earth

                                                  Found evidence that more organisms had vanished from

                                                  Earth (Researchers estimate that of all the species that

                                                  have lived on Earth, more than 99.9% are now extinct)

                                                  Wrote the book The Origin of Species by Means of

                                                  Natural Selection in 1859.

Darwin’s Ideas

Fitness – the ability to which the physical traits and behaviors enable organisms to

               survive and reproduce in their environment

Evolution – change in species over time produced modern organisms

Common descent – idea that species have descended from common ancestors

                                just as each new organism comes from preexisting organisms, each

                                species descended from other species over time

Adaptation – process that enables organisms to become better suited to their

                     environments; better able to survive and reproduce

                     inherited characteristics that increase an organism’s fitness for survival

Influences on Darwin

Geology:  Charles Lyell wrote the book Principles of Geology, convincing Darwin that

                 the earth was much older than believed

                 vast amounts of time are essential for evolution to occur

Farmers:  Farmers altered and improved crops and livestock through breeding programs.

                Farmers convinced Darwin that many of these variations were often passed on

                to the animals’ offspring.  They were inherited variations.  Darwin realized that

                farmers could not cause variation to occur.  Variation either happened naturally

                or it did not. Once farmers encountered variation, they could use it to their

                advantage.  They noted the variations they found and decided which organisms

                to use as breeding stock.  Darwin called this process artificial selection.

               Artificial selection allowed only the individuals who suited the farmers’ needs

               to produce offspring. In artificial selection, the intervention of humans ensures

               that only individuals with the more desirable traits produce offspring.  Darwin

               was convinced that a process similar to artificial selection must be at work in

               nature.

Malthusian Doctrine:  Economist Thomas Malthus observed that babies were being born

                                    at a faster rate than people were dying.  The only conditions that

                                    would prevent the endless growth of human populations, were

                                    famine disease and war. (Malthusian Doctrine) Darwin realized

                                    that the Malthusian Doctrine applied to all organisms. Thousands

                                    upon thousands of individuals of each species die, and only a few

                                    survive.  Even fewer successfully raise offspring.  What

                                   determines which individuals survive and reproduce?

DARWIN’S THEORY OF EVOLUTION BY NATURAL SELECTION

1. Overpopulation – favorable conditions allow a population to increase in size

                                   Environmental pressures limit the number that can survive

2. Variation – no 2 organisms in a population are exactly alike

3. Competition – due to environmental pressures organisms must compete

      4.  Survival of the fittest – the individuals who are best adapted to the environment

                                                are most likely to survive

                                                they possess variations that give them an advantage

5. Reproduction – individuals that survive can reproduce and pass traits to offspring

      6.  Speciation – the population changes because some traits are passed on and others

                               are not

                               when a population differs enough from the original population it is a

                               new species

EVIDENCE OF EVOLUTION

1. fossil record – fossils are the preserved remains of ancient organisms

                              some of these fossils resemble organisms still alive today

                              the fossil record represents the preserved collective history of the

                              Earth’s organisms

                              the fossil record shows that change followed change on Earth

                              Relative dating – a method of determining the age of fossils by

                              comparing them to other fossils in different layers of rock

                              Relative dating cannot determine the actual age of fossils but can

                              be used to determine which fossils are older and younger than each

                              other.  Fossils in lower rock strata are older than fossils in upper

                              rock strata.

                              Radioactive dating – a method of determining the age of an object

                              by measuring the amount of a specific radioactive isotope it

                              contains.  Radioactive dating can be used to determine the actual

                         age of fossils.  Uranium-238 and potassium-40 are used to determine

                         the age of very old fossils.  Carbon-14 is used to determine the age of

                         fossils less than 60,000 years old.

2.  DNA analysis – DNA of eukaryotic organisms always has the same basic structure

                                and replicates in the same way.  The structural and biochemical

                                similarities among living organisms are best explained by

                                Darwin’s conclusion:  living organisms evolved through gradual

                                modification of earlier forms (descent from a common ancestor)

                                RNA is similar in structure from one species to another.

                                ATP is the energy carrier in all organisms.

                                Many proteins, such as cytochrome c, are shared by many

                                organisms.

3.Artificial selection – breeding organisms by humans for specific phenotype

                                   characteristics

                                   choosing the appearance of an organism for breeding based on

                                   appearance increases the chances of having those desired

                                   characteristics in the offspring

4. Morphology – homologous structures – parts of different organisms often quite

                             dissimilar that developed from the same ancestral body parts.

                             Example: human arm, whale flipper, bat wing, and dog leg have the

                             same arrangement of bones.

                            Vestigial organs – structure that serves no useful purpose or

                             function in an organism.  When organs may be eliminated or

                             reduced in size leaving only a remnant of what was once an

                             important part of the animal can be a clue to the animal’s

                             evolutionary ancestry.  The human appendix is an example of a

                             vestigial organ.  Humans have a set of miniature tail bones at the

                             base of the spine which are vestigial structures.

5. Embryology – Embryo – organism at early stages of development

                              Embryos of many different animals look similar and are hard to

                              tell apart.  Hox cluster establishes the pattern of arrangement of

                              structures from head to tail.  The common patterns of embryonic

                              development in vertebrates occur because all vertebrates share the

                              same basic control mechanism.  Evolution acts on mutations which

                              are changes in DNA. 

6.  Viral evolution – Viruses (infectious particles composed of a protein capsule and a

                                  nucleic acid core, which is dependent on a host organism for

                                  replication) often take host DNA with them when they replicate.

                                  This changes the viral genetic make up causing the virus to

                                  evolve.  This is the cause of the fear that the Bird Flu Virus

                                  could mutate and be able to affect people.

6. Geographic distribution of related species – one of the most common ways in

                                                                             which new species form is when

                                                                             populations are separated.  The

                                                                             separation of populations so that they

                                                                             do not interbreed is called

                                                                             reproductive isolation. Kaibob

                                                                             squirrels at the Grand Canyon are an

                                                                             example.  Related species will

                                                                             usually be in close proximity.

7. Antibiotic and pesticide resistance in various organisms – Many bacteria become

resistant to antibiotics because those which are naturally immune to  the drug are the only ones that survive and reproduce so the immunity is passed on to the offspring.  Many insects become immune to pesticides because only the ones naturally immune to the chemicals survive and reproduce.  Natural selection chooses those that survive the chemicals to reproduce.

COMPARE AND CONTRAST LAMARCK’S EXPLANATION OF EVOLUTION WITH DARWIN’S THEORY OF EVOLUTION BY NATURAL SELECTION

Compare:

Both realized organisms changed over time

Both realized species adapt to their environment over time

Contrast:

§         Lamarck thought organisms change because they have an inborn urge to better themselves

§         Lamarck thought that change occurred through use and disuse – organisms could alter their shape by using structures in different ways

§         Lamarck thought acquired traits were inherited

Darwin believed the following steps led to evolution by natural selection:

§         Overpopulation – favorable conditions allow a population to increase in size

                                   Environmental pressures limit the number that can survive

§         Variation – no 2 organisms in a population are exactly alike

§         Competition – due to environmental pressures organisms must compete

§         Survival of the fittest – the individuals who are best adapted to the

                                                       environment are most likely to survive

                                                       they possess variations that give them an advantage

§         Reproduction – individuals that survive can reproduce and pass traits to

                               offspring

§         Speciation – the population changes because some traits are passed on and

                                      others are not

                                      when a population differs enough from the original population it

                                      is a new species

Evolution – the long-term process through which a population of organisms accumulates

       genetic changes that enable its members to successfully adapt to

       environmental conditions and to better exploit food resources

Cladogram – a branching diagram that illustrates taxonomic relationships based on the

                      principles of claudistics

Claudistics – classification based on evolutionary history

Cladograms

Individuals whose characteristics are well-suited to their environment survive.  Individuals whose characteristics are not well-suited to their environment either die or leave fewer offspring.

Genes, the carriers of inheritable characteristics, are also the source of the random variation upon which natural selection operates.

When variations occur natural selection selects the successful ones.

Natural selection can operate only on the phenotypic (appearance) variation among individuals.

All members of a population can interbreed so they and their offspring share a common group of genes called a gene pool .

The number of times an allele (different form of a gene) occurs in a gene pool compared with the number of times other alleles for the same gene occur is called the relative frequency of the allele.

Evolutionary change involves a change in the relative frequencies of alleles in the gene pool of a population.

No two species can occupy the same niche (combination of an organism’s habitat and its role in that habitat. in the same location for a long time.

Adaptive radiation or divergent evolution is when one species gives rise to many species.

Convergent evolution phenomenon in which adaptive radiations among different organisms produce species that are similar in appearance and behavior.  Convergent evolution has produced many analogous structures in organisms today.  Analogous structures are similar in appearance and function, but they have different origins.  The wings of butterflies and birds are analogous structures.

Gene pools can change in the absence of natural selection.  This random change in the frequency of a gene is called genetic drift.

Living fossils are species particularly well adapted to an environment that do not change over time, example horseshoe crab.

Mass extinction – one of the brief periods of time during which large numbers of species disappeared. Some mass extinctions were caused by changes in global climates that altered many environments.  The causes of other mass extinctions remain uncertain.  The species that remain suddenly find lots of empty niches.  Groups of animals with enough genetic variability can undergo adaptive radiations and produce a large number of new species to fill those empty niches.

Era	Period	Epoch	Ma*
C E N O Z O I C	Neogene	Pleistocene	2
		Pliocene	5
		Miocene	25
	Paleogene	Oligocene	38
		Eocene	55
		Paleocene	65
M E S O Z O I C	Cretaceous	Late	97.5
		Early	144
	Jurassic	Late	163
		Middle	188
		Early	213
	Triassic	Late	231
		Middle	243
		Early	248
P A L E O Z O I C	Permian	Ochoan	256
		Guadalupian	258
		Leonardian	268
		Wolfcampian	286
	Pennsylvamian	Gzelian	?
		Kasimovian	?
		Moskovian	?
		Bashkirian	320
	Mississippian	Serpukhovian	333
		Visean	352
		Tournaisian	360
	Devonian	Famennian	367
		Frasnian	374
		Givetian	380
		Eifelian	387
		Emsian	394
		Siegenian	401
		Gedinnian	408
	Silurian	Pridoli	414
		Ludlow	421
		Wenlock	428
		Llandovery	438
	Ordovician	Ashgill	448
		Caradoc	458
		Llandeilo	468
		Llanvirn	478
		Arenig	488
		Tremadoc	505
	Cambrian	Merioneth	523
		St. David's	540
		Caerfai	590

Biological evolution is defined as a change in allele frequency of a species or population over time.  Biological evolution is best summarized in Darwin’s theory of natural selection.  Populations grow, but environmental factors limit the number of individuals that can survive.  Variation among the individuals gives some an advantage as they compete for resources.  The ones with the best genes for survival are the ones that survive and reproduce, increasing the frequency of those genes that give them an advantage in the population.  Genetic drift can also change gene frequencies just by chance, not because they are better adaptations.  Genetic drift occurs most efficiently in small populations.  Genetic drift implies that all characteristics of an organism do not have to contribute to fitness.