Chapter 17

Evolution’s History Perspective

http://www.pbs.org/wgbh/evolution/religion/revolution/index.html

Popular Beliefs up through the 1800s

Commonly held beliefs were not based on looking at the world, or examining nature.

They were based on stories handed down from generation to generation, in both oral and written forms. The Bible and Catholic dogma was the most influential force on thought.

Therefore, when the world and nature was examined, anything that was observed was interpreted according to what was already believed.

Beliefs based on these forces:The earth was young.Species were made and did not change.

When observations were made that did not fit what was already believed, new theories were contrived to fit the data into the context of what was already believed.

Jean-Baptiste Lamarck (1744-1829)A major contributor to Cell TheoryOne of the first to use “biology” in its modern senseStarted out as an “essentialist” who believed species did not change. But his own work on mollusks convinced him that change had to have occurred.Was the first to propose a cohesive theory of evolution (inheritance of acquired characteristics)

Popular Beliefs up through the 1800s

George Cuvier (1769-1832): paleontologist, father of comparative anatomyHe worked with fossils (he found and named pterodactyl in Bavaria).He thought Lamark’s ideas were ridiculous, and firmly believed in the fixity of a species.He came up with the principle of “correlation of parts” – The notion that comparative anatomy was so accurate that after inspecting a single bone, the class and sometimes genus of an animal could be inferred.This is because the number, direction, and shape of the bones composing each part of a body are always in a necessary relation to all parts such that a great deal can be inferred with only a few bones.That was in 1798.

He believed (because he was really left with no other choice) that the fossil remains he worked with must be that of extinct species.

Because he lived in a society dominated by religious thought – and he was a close personal friend of a cardinal, apparently – he had to fit his observations into the context of the creationist account that the earth was young.

He therefore proposed that “All of these facts, consistent among themselves, and not opposed by any report, seem to me to prove the existence of a world previous to ours, destroyed by some kind of catastrophe”

To reconcile belief with his observations he developed the theory of catastrophism, which is sometimes called “Cuvier’s Compromise”.

Catastrophism was the idea that a young earth’s history was defined by an accumulation of brief yet violent natural catastrophes. Localized natural disasters would whip out all life in one region, and new species from other regions would repopulate the barren area.

From a biography found here: All extinct forms of life found in the fossil record were formed in a dark mysterious antediluvian period (before the flood).

Due to his protestant beliefs, Cuvier carefully described his antediluvian period having multiple floods of the last being the biblical flood.

When defining this period he gave it an unknown time length which corresponded with the concept that earth was in fact very old…

It was assumed that rocks and sand precipitated out of an enormous flood. This theory was called Neptunism.

James Hutton (1726 – 1797) founder of modern geology

His geological observations suggested that the earth was very, very old. Neptunism – and therefore, catastrophism – could not be correct.

They called his theory Plutonism. The earth was hot inside, which was the only way to explain the observed geology.

The notion of “deep time” arose from his work.So did Uniformitarianism: The assumption that the

natural processes operating in the past are the same as those that can be observed operating in the present – “the present is key to the past”

He wasn’t a very good writer, and his ideas didn’t catch on until others popularized his work (mostly, Lyell, see below)

He believed that species could adapt, but the notion of selection giving rise to new species was a “romantic fantasy”

Sir Charles Lyell (1797 – 1875)

His father was a lawyer and botanist. So he followed his father into law. Until his eyes started to get bad; then he took up geology (he spent a lot of his childhood at a famous hunting lodge)

He worked under William Buckland, at Exeter College in Oxford, who did NOT like Hutton’s work on Uniformitarianism, as it countered the existence of the flood. Buckland developed a theory to reconcile the biblical account – Flood Geology -- in 1820. This was found in “the Connexion of Geology with Religion”. In this he reconciled Hutton’s theories with the notion that the word “beginning” in Genesis meant an undefined period of time. Old World Creationism is born.He also wrote the first full account of a fossil dinosaur.

Lyell was rare in that he managed to support himself by writing books (how this helped his eyesight, I have no idea). He wrote Principles of Geology , in which he popularized the theory from 30 years ago (Hutton’s) that the earth was very old, based on geographical data.

Evolution by natural selection A. Explain the historical context, include fixity of species. B. Discuss Darwin’s contributions: Theory of Evolution by Natural Selection.

1. His proposed mechanism for evolution: “Natural Selection, and his published body of evidence for evolution in Origin of Species.

Use the definitions: Darwinian: “descent with modification” and the modern synthesis with genetics: “change in allele frequency in a population over time.” Reminder: populations evolve, not individuals

2. Describe Lamarckian “inheritance of acquired characteristics” 3. Compare and contrast with Lamarckian “inheritance of acquired characteristics”

C. Identify the Requirements of Natural Selection: 1. Phenotypic variation: importance of environmental vs. genetic determination of phenotype 2. Variation with genetic basis, “heritable” 3. Differential fitness of the variants Define fitness: proportional genetic contribution to the next generation 4. Identify: differences in individual reproductive success leads to greater “adaptation” of a

population to its environment.

Members of a population vary.Microevolution deals with evolutionary changes within a population (recall

the definition!)Population Genetics concerns itself with allele frequencies within a

population.The gene pool is the total number and amount of alleles for every single gene

of a particular population.Recall simple mendelian geneticsLet the trait “wing size” be represented by “L” and “l”. (Long wings are

dominant)So, individuals can be

LL (homozygous dominant)Ll (heterozygous)ll (homozgous recessive)4

LL Ll ll

If we have 100 flies in a population, we have 200 total alleles (everyone has 2 copies of each factor)

36% of the flies are LL, 48% are Ll, and 16% are ll.

How many L total? 120 out of 200, or 60%How many l? 80 out of 200, or 40%Let’s do a population genetic’s Punnett

square

36% 48% 16%

The allele frequency does not change in the next generation. Sexual reproduction alone cannot bring about a change.

LL Ll ll

The English mathematician Godfrey Harold Hardy and and German physican Wilhelm Heinberg independently came to the same mathematical truth about population genetics.

36% 48% 16%

LL Ll ll

Using simple algebra…

Let p represent “L”Let q represent “l”Since there are only 2 alleles, p+q = 1 (or 100%)

So LL = pp, Ll = pq, and ll = qq.

… p*p = p2 and … q*q = q2

Since the total number of possibilities is simply the sum of all the genotyes, we have:

p2+q2+pq+pq, or to put it in its organized state:

p2+2pq+q2 (think of FOIL from math, (p+q)(p+q))

Since the total sum is 100% (or just 1 in probability math):

p2+2pq+q2 = 1

36% 48% 16%

LL Ll ll

Summary: we know thatp+q = 1p2+2pq+q2= 1 (a binomial

expression)

Therefore, we can derive allele frequencies based on the population statistics!

36% 48% 16%

The Hardy-Weinberg Principle The Hardy-Weinberg Principle states that an equilibrium of allele frequencies

in a gene pool will remain in effect in each succeeding generation of sexually reproducing population as long as five conditions are met.

1: No Mutations2: No Gene Flow3: Random Mating4: No Genetic Drift5: No Selection

Any violation of these conditions will result in a shifting of allele frequencies – and a change in the population over time – evolution.

Example: Industrial melanism

1: No MutationsWe now know that mutations will happen, and be random.

Mutations that affect an allele’s expressed phenotype will result in a change in the population.

Most traits have several phenotypes – they are polymorphic.A polymorphism is simple a difference within a population’s

genotype.About 30% of fruit fly genes are polymorphic (Lemontin &

Hubby)Combinations of alleles (not just 1 difference) may confer

selective advantage. This will arise during recombination.Daphnia, pg. 304.

2: No Gene FlowDefinition: Movement of alleles between populations.

Result of the migration of breeding individuals.Increases genetic variation of a population by introducing

new alleles produced by mutation in another population.

Makes gene pools similarReduces allele frequency differences between 2

populationsCan prevent speciationTends to decrease genetic diversity amongst different

populations of the same species.

3: Nonrandom matingInbreeding: Breeding between relatives to an extent higher than random

chanceDecreases heterozygote frequency, increases homozygote frequency.Danger of increasing recessive abnormalities

Assortive Mating: Mating between the same phenotypeCauses subdivisions within a populationHomozygotes increase, heterozygotes decrease.Can be seen in the human species!

Sexual Selection: Males compete for the right to reproduce; females choose males with particular phenotypes.(These phenotypes generally relate somehow – directly or indirectly – to the male’s ability to provide resources for the female and her young)

4: Genetic DriftChange in allele frequency due to chance.Large populations are less affected than small.Loss of all breeding individuals with a particular allele by chance will

shift the allele frequency. Usually happens only to small populations.

Experimental Evidence: Drosophila107 bottles, each with 8 Ll. After the bottles are populated, 8 random males + 8 random females are

removed and put into a new bottle.After 19 generations,

25% of the bottles were 100% aa25% were 100% AA50% of the bottles were Aa

Therefore, give the starting conditions (a “founder” population of 8 random flies), there is a 50% chance that the new population will completely lose this polymorphism and become uniform in this trait.

More Evidence: Cypress trees in CA

4: Genetic DriftBottleneck Effect: near extinction from natural

disaster/overhunting/deforestation/habitat lossExample: Cheetah

Founder’s Effect: a small population breaks off from a larger. Rare alleles – or rare combinations of alleles – occur at a higher frequency

in a population isolated

(key difference: the remaining populations are still alive)

5: Selection• When there is an unequal chance that offspring will survive

and reproduce.• Conditions:

– Inheritable variation within a population (phenotypic variations are genetic)

– Differential adaptiveness – some of these variations affect the ability of an organism to adapt to its environment (to be “comfortable”)

– Differential reproduction – those more adapted will have more offspring. “Their fertile offspring will make up more of the next generation’s gene pool”.• This ultimately determines “fittness”.

• Relative Fitness: Comparing the ability of one phenotype to reproduce better or worse than another.

Types of Selection

• Most traits acted upon by natural selection are polygenic – traits governed by more than one pair of alleles, located at different genetic loci.

• In general, most traits (phenotypes) fit within a RANGE, or distribution, that usually falls onto a bell curve.

Types of Selection

Directional Selection occurs when an extreme phenotype is more fit.

Examples: HorsesInsects (DDT)Malaria (chloroquinone)

Types of Selection

Stabilizing Selection occurs when an intermediate phenotype is favored.

Examples: Swiss Starling Clutch Size

determined byyolk productionlength of mating

Human Birth Weight

Types of Selection

Disruptive Selection occurs when either extreme phenotype is favored.

Examples: British Land Snails

Maintenance of Variation

D. List the Origins of genetic variation in a population: 1. Ultimately, all originates from mutations (random, not arising in

response to “need”) 2. Sexual recombination a. independent assortment in gamete formation b. crossing over c. new allele combinations resulting from sexual fertilization d. larger-scale mutations, e.g., chromosome duplications, polyploidy

E. Discuss the major lines of evidence which support the principle/theory of evolution. Include: comparative anatomy (homologous vs. analogous

characters),biogeography, fossil record, molecular biology (e.g., amino acid and nucleotide sequencing, ubiquity of genetic code and fundamental biochemical pathways) embryology and development.

F. Discuss the controversies surrounding evolution.

Young Earth or Old Earth?• Observation: Earth.• Hypothesis 1: Earth is Young.• Hypothesis 2: Earth is Old.• Prediction 1

– If earth is young, then short-lived radioactive materials will be found in the crust.

– If the earth is old, only long-lived radioactive materials will be found.• Experiment 1: Test for the presence of long and short-lived

radioactive material in the earth’s crust.• Data: Only radioactive materials with half-lives of greater than 80-

million years old are found in the crust, except those generated by current natural processes (such as cosmic radiation’s generation of carbon 14 from nitrogen 14) (source)

Young Earth or Old Earth?

Young Earth or Old Earth?• Prediction 3

– If the earth is young, there will be no evidence of long-term environmental phenomenon.– If the earth is old, there will be evidence of long-term environmental phenomenon.

• Experiment: Sample the earth for long-term phenomenon.• Data:

– Loess deposits (deposits of wind-blown silt) in China are 300 m thick. They give a continuous climate record for 7.2 million years. The record is consistent with magnetostratigraphy and habitat type inferred from fossils (Ding et al. n.d.; Russeau and Wu 1997; Sun et al. 1997).

– Varves are annual sediment layers that occur in large lakes. They are straightforward to measure, cover millions of years, and correlate well with other dating mechanisms• Dates obtained by counting annual layers of varves match dates obtained from radiometric

dating. One varve formation, covering 45,000 years, was used to calibrate carbon-14 dating using terrestrially produced leaves, twigs, and insect parts that also appeared in the sediments. The varves were easy to count because they included an annual diatom bloom (Kitagawa and van der Plicht 1998).

Young Earth or Old Earth?• Prediction 4:

– If the earth is young, then the sun is also young.– The sun is old.

• Experiment:– Measure the age of the sun.

• Data– The abundance and distribution of helium change predictably as

the sun ages, converting hydrogen to helium in its core. These parameters also affect how sound waves move through the sun.

– Thus one may estimate the sun's age from seismic solar data. – Such an analysis puts the age of the sun at 4.66 billion years,

plus or minus about 4 percent (Dziembowski et al. 1999).

A word of caution.• Modern science holds evolution as a theory on the same level of cell theory, the

theory of electromagnatism, the theory of relativity, etc.• A scientific theory is NOT a theory in the common way the word is used.• A scientific theory is derived from a hypothesis (based on observations) of which

– a great deal of experimental data is in agreement with from many different sources– No experimental data directly refutes the theory

• Creationists would have you believe that evolution is a hypothesis based on incorrect conclusions drawn from faulty data.

• A typical scientist rejects this to be wrong. Biology as a science – as we know and understand it today – would make NO sense is evolution is false.

• We therefore talk about evolution the same way we talk about atomic structure. To the absolute best of our current ability to observe and probe the world around us, it serves as a basis from which many new discoveries are made.

Young Earth or Old Earth?• Prediction 5:– The young earth has an appearance of age (the Omphalos

argument)– The old earth will also have an appearance of history, not

just age.• Logical problem 1: “apparent” age and real age are indistinguishable from

one another. Therefore, “apparent” age is not falsifiable. True age, however, is.

• Logic problem 2: a young earth with ‘appearances’ of age will have light falling on it from supernovas that never really existed.

• Logic problem 3: the lack of oxygen content in the early earth (which is the dominant scientific view based on evidence here) will have had to have been faked.

• Logic problem 4: All fossil evidence must have been faked.• Logic problem 5: radiomimetic dating must be completely wrong.

• Prediction 6:– If the earth is young, and humans were created at its origin, then humans and

dinosaurs once lived together.• Therefore, human and dinosaur remains should be found if not together, at least on the

same geological layer.– Dinosaurs went extinct long before humans evolved.

• Therefore, human and dinosaur remains will be in different geological layers and have different ages according to other means of age estimation.

• Experiment: Examine any available evidence and arrive at a logical conclusion.

• Data: – To date, no human fossils have been found next to dinosaur fossils.– There is a ~64 million year gap in the fossil record where neither dinosaur nor

human fossils are found. – If nothing else, there should not be such a dramatic separation between them.

• Even if they were found together, this does not argue against evolution.

Genesis vs. Modern ScienceGenesis• a beginning• primitive earth in darkness and enshrouded

in heavy gases and water• Light• an expanse or atmosphere• large areas of dry land• land plants• sun, moon, and stars discernible in the

expanse, and seasons beginning• sea monsters and flying creatures• wild and tame beasts and mammals; • Man.

Modern Scientific Thought• a beginning• Light• sun and stars• primitive earth, moon, and atmosphere• dry land• sea creatures• some land plants• land creatures and more plants and sea

creatures• flying creatures (insects) and more plants

and land and sea creatures; • mammals, and more land and sea animals,

insects, and plants• the first birds• fruiting plants (which is what Genesis talks

about) and more land, sea, and flying creatures

• man and more of the various animals and plants.

Genesis does NOT have the order of creation right.

• Example: “Archeopteryx is NOT a hoax, it is a true bird, not a missing link” (thanks to Pedro for the link).– This “truth” is based on a single quote from an evolutionary

biologist that simply disagrees that archeopteryx is a missing link.

– This scientist still believes in evolution, just does not agree that other scientists think this is a missing link.

– Scientists classify fossils based on their structure. Archaeopteryx shares characteristics of both birds and reptiles.

• Arguments against evolution never postulate alternative scientific theories. “Intelligent Design” is not a scientific theory. This has been shown time and again by basic scientists, as well as the Delaware Supreme Court.

Archaeopteryx has many more reptilian features than those of modern birds

• Bird FeaturesWings for flightTrue feathers*Wishbone (furcula)*Bipedal*Bones pneumatic*Reversed big toe*

• Reptile FeaturesBony tail with free vertebrae3 claws on wingLong snout; no beakJaws with teethFlat breastboneTrunk region vertebrae are not fusedElongated cerebral hemispheresSkull and brain reptilianConcave cervical vertebraeRibs slender and don't join sternum6 sacral vertebrae (birds have 11-23)Wrist joint flexibleNasal opening far forward on snoutFibula equal in length to fibulaFoot bones free"Ventral ribs" present in abdominal wall

* Indicates features recently found to be represented in dinosaur fossils.

Example: Archaeopteryx• http://ublib.buffalo.edu/libraries/projects/cases/skeletons_notes.html• Creationists use several arguments to devalue Archaeopteryx as a transitional species. • (a) The most common argument is that Archaeopteryx is simply a bird. "The so-called intermediate

is no intermediate at all because, as paleontologists acknowledge, Archaeopteryx was a true bird -- it had wings, it was completely feathered, it FLEW... It was not a half-way bird, it WAS a bird." (Gish 1978, p. 84).

• Gish is correct; we do classify Archaeopteryx as a bird by virtue of its wings and feathers. But it is not like any other bird -- extinct or modern. Except for the feathered wings, it is more like a reptile than a bird. That is why it was misidentified as a small dinosaur on some occasions. We do not have a taxonomic category for a half-way bird/reptile. If we did, we would put Archaeopteryx in it.

• (b) Another argument is to claim that Archaeopteryx is a forgery. They are picking up on the absurd claim made by two controversial astronomers, Hoyle and Wickramasinghe. This allegation, never entertained seriously by paleontologists, was effectively demolished by scientists of the British Museum (Charig et. al., 1986).

• (c) Creationists have argued that Archaeopteryx can't be transitional because true birds existed several million years before Archaeopteryx. It is possible that true birds existed before Archaeopteryx. Sankar Chatterjee of Texas claims that he has a specimen he named Protoavis that predates Archeopteryx by 75 million years. This can't be confirmed because Chatterjee refuses to let other paleontologists examine his specimen, and even he has not been able to find evidence for feathers. Finally, even if Protoavis is a "bird" rather than a small dinosaur, then it would simply assume the title of the earliest reptile-bird transition!