Evolution Unit

General Terms for Evolution and Worldviews

• One of the reasons "evolution" can be a divisive topic is the word can be used to refer to a variety pf different things
• It is helpful to define two broad types of evolution:

1. 1.      Microevolution:

Variations/ changes within a species

EG) changes within different types of dogs

• This is the most readily observed type of evolution and is often used as the proof/ support for alternate versions of evolution

1. 2.      Macroevolution:

• Marco = large, micro = small
• Macroevolution is the creation of a new species from a pre-existing species

EG) humanoid --> human

EG) fish-like species to amphibian likes species

• Aside from the different types of evolution it is important to differentiate between the different worldviews (ways to view the world) that people have when it comes to evolution

1. 1.      Biblical Creationism:

• Based on a literal interpretation of the first chapters of Genesis
• Literal 6 days to create the cosmos, earth, and all life forms
• Humankind and other lifeforms were created to their kind and have no common ancestors
• Interpret fossil evidence as primarily a result of a cataclysmic flood
• Young earth, less than 10,000 years old
• Also known as young earth creationist

1. 2.      Progressive Creationism:

• The view that God progressively mode the Universe, NOT in on instant
• This view says the Universe is Ancient (billions of years etc.)
• Interpret, progressive creationist believe humanity is very young (thousands of years)
• Old earth, Young humanity
• Still, belief in account of Genesis ch.1-3 with regards to humans

1. 3.      Theistic Evolution:

• Merge creation with evolution
• Believe God used evolution to create humanity
• Interpret Genesis 1-3 as poetry and a "day" as an era of time not a literal 24 hours
• Old Earth and Old Humanity
• Still, believe in God but just that He used lower life forms to make humans

1. 4.      Atheistic Evolution:

• Believe the Earth is Ancient and that humans are the result of evolutionary processes
• DO NOT believe in Intelligent Design
• Intelligent Design (ID) says there is an outside person who is responsible for making the physical/ material world
• People who believe in atheistic evolution hold a materialistic belief that there is nothing beyond the material/ physical world

Population Equilibrium

• Populations are always experiencing two competing factors: the tendency to remain stable (unchanged) and the tendency towards variability (change)
• When the tendency to remain constant wins out it is called genetic equilibrium and only if it is upset can the population evolve
• The conditions which allow no change to occur are:
  • Large populations … ensures changes are not a result of chance alone
  • Random mating … a preference is not given to passing along only certain genes
  • No mutations … the genes are remaining the same
  • No migration … no new genes entering or leaving the population
• In 1908, the Hardy-Weinberg principle was made to describe the conditions under which allele and gene frequencies will remain constant from generation to generation (equilibrium)
• The principle predicts that if all other factors remain constant the gene will have the same composition generation after generation

Hardy-Weinberg Equation

P² + 2pq + q² = 1                                                                p = frequency of dominant allele

P + q = 1                                                                               q = frequency of recessive allele

• If the values for p + q are known, this equation can be used to determine the three genotypes percentages (i.e. two homozygous types and 1 heterozygous type)
• Consider the following example:
• There are two variations of a specific gene: A + a
• There are therefore three possible genotypes: AA, Aa, aa
• However A's frequency = 0.6 and as frequency = 0.4 so, p² + 2pq + q² = 1 calculate using the Hardy-Weinberg principle and a Punnett Square

Evidence for Microevolution

• A population's gene pool is very unstable because it is constantly influenced by external factors that try to change its makeup
• Evolutionary change occurs in a population's gene pool is altered. This change can be caused by 4 main things: Mutation, Genetic Drift, Migration and Natural Selection
• While changes in a population can occur because of any one of this equilibrium (i.e. microevolution)

1. 1.      Mutation:

• Mutations are changes in the genetic makeup of an organism
• Mutations come in two forms: chromosome mutation or gene mutation
• In chromosome mutations, the resulting gamete will either lack a particular chromosome or gain an extra one

EG) Down Syndrome is caused by an extra copy of chromosome 21

• In gene mutation, the result is a change/ alteration in an individual gene's DNA

EG) cystic fibrosis is caused by mutations in the gene that codes for a protein that helps make secretions (sweat, digestive fluids, mucous etc.) and when this protein is not present secretions become thicker

• There is general agreement among scientists that mutations are the original source of variations/ microevolution
• However, most observed gene mutations have a negative effect on an organism - not a positive
• Studies have been done on bacteria, corn and humans are show mutations occur at a rate of approx. 1 per 500,000 genes
• This is rare, but because each individual has so many genes, and there are so many individuals in a given population, new mutations occur
• Whether a mutation is an advantage to an individual depends on their environment

EG) what is good in one environment might be bad in another and vice versa

1. 2.      Genetic Drift:

• Also called "random genetic drift"
• Genetic drift is the variation in how frequently different genotypes appear in a small population
• Genetic drift can disrupt genetic equilibrium in small population because chance has a larger impact than on a big population

EG) it's not likely to roll the same number with a die twice in a row but it is extremely rare to roll the same number 100 times in a row

EG) consider a population of only 10 guinea pigs, with 1 of the 10 with a black fur coat allele (B). If by chance, the black individual doesn't mate, the black allele will disappear from the population … this would not happen if the population were significantly larger and 10% of it had the black allele.

1. 3.      Natural Selection:

• Darwin's theory of evolution by natural selection can be divided into 5 distinct ideas: overproduction, struggle for existence, variation, survival of the fittest, origin of a new species
• All 5 of these ideas contribute to the understanding of how nature can "select" certain desirable traits to be passed along and other undesirable traits to not be passed along to future generations

1. A.     Overproduction:

• Overproduction means the number of offspring produced by a species s greater than the number that can survive

EG) millions of eggs are annually laid by female codfish … if all of them were to survive, the ocean would be filled solid in a few years

EG) babies produced --> resources + places to live

1. B.      The struggle for Existence:

• Because of overproduction, organisms of the same species (as well as other species competing for similar resources), must compete for limited resources such as food, water and a place to live

1. C.      Variation

• No two individuals are the same
• Differences among individuals result in a widely varied population of any given species

1. D.     Survival of the fittest

• Also known as "natural selection" through it really is smaller part of a larger idea
• Individuals with traits that give them an advantage are better able to compete survive and reproduce
• Those that are well adapted to their environment, over and above other individuals, are "filled" to survive overproduction and the struggle for existence

1. E.      Origin of a New Species

• This final part of N. Selection is debated as it no longer is about changes in an existing species (microevolution) but rather the creation of new species (macroevolution)
• Darwin believed that over numerous generations, new species arise the accumulated effect of inheriting variations
• He saw this could result in new individuals emerging to the point that they are so different from their ancestors that they are no longer even the same species
• The creation of new species is called speciation

Natural Selection & Migration

• Both of these forms of migration cause a disruption to genetic equilibrium and can, therefore, be a cause of macroevolution

1. 4.      Migration

• Migration  is the movement of members into (immigration) or out of (immigration) of a population
• Immigration results in the addition of new genes and immigration results in the subtraction/ removal of genes from a gene pool

Macroevolution

Evidence for Macroevolution ad Alternate Explanations:

• Often times the word "evolution" is used as a positive and associated with progress

EG) Justin's understanding of Math has evolved over time

• There are a number of observed evolutions that are in fact damaging or even deadly to populations

EG) Most observed genetic mutations harm te organism in question

• Evolution is neither a positive or negative, it simply means: change over time
• There is the amount of evidence that is used to support the Theory of Evolution that we will study: Adaptive Radiation, Convergent Evolution, Embryology, Vestigial Physiology, Coevolution, the Geological Column and Fossil Dating. Transitionary Fossils and Genetics.
• In each instance, we will study what the main idea is, examples used to support it, and lastly what are some alternate explanations given to see the evidence in a different light

1. 1.      Adaptive Radiation:

• Adaptive radiation: the evolution of many species from one common ancestor
• Normally believed to happen relatively quickly due to a change in environment

EG) darwin's finches… one bird type evolved into varied types of that bird within a relatively short amount of time because the environment of the Galapagos Islands is different from their native environment.

• Alternate Explanation: these are examples of microevolution and not actual proofs of macroevolution

EG) if two people were accused of a crime, the proof of one person guilt can't/ shouldn't be used as the basis for convicting the other person

1. 2.      Convergent Evolution:

• Convergent evolution is the process of two or more species evolving similar traits independent of one another because they are exposed to similar environments

EG) both bats and birds have a similar wing structure even though they are not related

• Convergent evolution involves comparative anatomy and homologous parts
• Comparative anatomy is the study of structural similarities in different species
• Homologous parts are similar structures but have different functions

EG) a forelimb on a bird is built similarly to a human forearm

• Alt. explanation:
• Is is not the observation of new species, just that various species have things in common
• Simply shows that similar environments place similar pressures on organisms whether they are related or not

1. 3.      Embryology:

• Embryology is the study of organisms in the early stages of development
• Comparative embryology shows the similarities of embryos from different species and how they are/ might be related
• In the 1800s comparative embryology began when scientists noticed the embryos of different species had similar features
• In 1868 Ernest Haeckel published the theory that suggests organisms have similar embryonic features because they are related and have common ancestors

EG) the human embryo has gill slits and a tail during its development

• Though there are indeed similarities, Haeckel embellished/ doctored his evidence to exaggerate the claim and was proven t be a found in this area
• The two similarities (for humans) are still true, however - our notochord and gill arches resemble other species in our embryonic form
• The notochord (precursor to the spinal cord) resembles a small tail
• The gills eventually form the tonsils and various glands.

• Alternate explanation: similar structures will have similar beggings

EG) if two organisms have a similar trait then it's not surprising that they have embryos that also resemble each other

1. 4.      Vestigial Physiology

• Structures that no longer serve a useful purpose are called vestigial organs
• At some point in the past, the organ was useful but not anymore

EG) appendix, tailbone, tonsils

• These are seen as evidence for macroevolution because it is believed that these organs were helpful for survival in the past but as the spec is evolved it is no longer beneficial/ needed

Alt explanation:

• Some of the organs are useful but not necessary for the species survival

EG)

­              the appendix does help the immune system contains lymphatic tissue

­              tailbone provides attachment for the muscles that keep you upright/ erect

­              tonsils are part of the immune system and help destroy harmful bacteria

Coevolution

• Coevolution is when two different species impact/ effect each other's survival
• Coevolution seems as a macro proof because the two most have evolved simultaneously

EG) bees and flowers are dependent on each other for their way of life

• There are numerous examples including very dramatic examples of insects having specialized parts that allow them to feed on a specific flower AND that flower alone being able to facilitate pollination of that type of insect
• Coevolution is closely related to symbiosis (means "live together" and describes how two organisms are involved in each other's life)
• The 3 main types of symbiosis are: mutualism, commensalism, and parasitism

              i.                Mutualism: both organisms mutually benefit

EG) Acacia tree ants defend the tree from attackers and are rewarded with the tee's fruit

             ii.                Commensalism: one organism benefits but the other is not harmed

EG) some fish live close the sharks that scare off the fish's predations

           iii.                Parasitism: some organisms can only survive by living off another organism/ host

EG) some worms need certain host to survive

Alt. Ex.:

• This is just an example of natural selection in that the first organism/ species is simply a part of the second organism's environment and helping to pass along desirable traits
• This mutual dependence is hard to produce without both organisms simultaneously being ready for the relationship… in other words, multiply the chance of one variation by the chance of the other variation

Geological Column + Dating Methods

• In geology, uniformitarianism is the view that Earth's geologic processes act today in some way they acted in the part
• This means that the key to understanding the past is present because you are assuming the manner rocks from/ interact today was the same way they interacted in the distant past
• From this belief, geologists have sequence of strata/ rock layers of various ages
• It is made of 12 layers that each represent 12 different eras/ time periods
• Fossils are not found equally throughout but much or presently in a few layers
• The layers were laid down over time so the deeper the layer the old it is
• There is an increase in complexity of the organisms from the bottom to the top
• Certain fossils are known as index fossils and are used to identify rock layers and time periods
• Based on the belief of a geological column, a geological time scale is proposed
• The geo. Timescale consists of divisions in time that correspond to major evolutionary events
• The time scale is divided into eons, eras, periods and epochs in a similar way we divide smaller amounts of time into years, months, days etc.
• One of the most famous evolutionary events that are believed to have happened is the Cambrian explosion
• The Cambrian Explosion is a dramatic increase in the complexity of life found in the fossils record in a relatively short layer/ period of time

In the layers prior to the C. Explosion, there are complete and diverse life forms yet during the layers that make up the C. Exp there is rapid speciation

Alt. Exp.

• It is only hypothetical as it does not exist anywhere on earth in its entirety

EG) Grand Canyon only has 1, 4, 5, 6 and 7

• A complete column would be 160 km thick
• Misplaced fossils have been found in the wrong layers

EG) plants found in levels before land life emerged

• There are polystrate fossils, large fossils that physically extend through layers that should have required millions of year to form
• The rough numbers are that it takes 1000 years to lay down 30 cm of sedimentary rock … this is based on uniformitarianism but what if there was a catastrophic event?

EG) an asteroid impact or the flood could alter the rate at which at which fossils are buried

• Radioactive dating has various problems and assumes a steady decay rate that may not be true

EG) as Uranium and Thorium decay they produce Helium, the 2^nd lightest element. Helium should diffuse out of a rock sample in less than 100, 000 tears but there are some rocks that are dated much older than that, that still have Helium atoms

1. 7.      Transitional/ Intermediate Fossils:

• Transitionary fossils are Intermediate Forms of Animals as they are evolving
• Macroevolution claims that all present species evolved from past species so there should be ample examples of transitionary fossils for all current skeletal species
• In humans, these are sometimes referred to as Missing Links
• There are various T. Fossils but the following is one of the best known

EG)

­              Archaeopteryx is an extinct species whose fossil remains are a blend of avian (bird) and reptile features

­              paleontologists view Archeopteryx as an example of a transitionary fossil

Alt Explanation:

• There should be considerably more T. Fossils found if macro evolution were true
• Archaeopteryx and other proposed fossils are not intermediate forms bu simply previous species that are now extinct