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Flashcards in Biology 11 Evolution Deck (30):

What is Evolution? Natural Selection?

Evolution: change over time in a line of descent
 More specifically, evolution is change in the gene pool of a population over time

Gene Pool: Set of all ALLELES for a particular trait/gene in all individuals of a population (pool of genetic resources)

Natural Selection: process in which environmental pressures result in the differential survival and reproduction of individuals of a population who vary in the details of shared, heritable traits.
-survival of the fittest


Charles Darwin

1800s Charles Darwin collected evidence and developed his theory of evolution and natural selection
-Darwin inferred All living creatures descended from a common ancestor
-Thought that over many generations, individuals with the most adaptive traits tend to survive longer and reproduce more than their less fit rivals.
-thought that some traits were more advantageous

-1831: voyage on the Beagle
-very respected man, feared the controversy of his theory
-many people believed in the bible (species were miraculously created by god)
• 23 years of work to finally publish his theory to the world: The Origins Of Species book →explains how evolution occurs →”Natural Selection”
o Had the courage to go against what was believed in those days
• Darwin theory explains how and why biology makes sense

Ex: differences in finches on the Galapagos, hummingbird beak length


Darwin vs. Wallace

• Wallace is called the father of biogeography (co-discoverer of natural selection)
• Darwin and Alfred Wallace both theorized natural selection. →Both tried to prove evolution rather than creationism

• Darwin, independently wealthy, had the benefit of leisurely study while Wallace faced financial hardship and gathered species to make a living.

• Wallace believed that the two varieties of the species were able to co-exist until changes in the environment forced the parent form to become extinct.

• Wallace focused on how selection “acted” on GROUPS or species as a whole with the most important force being the need for the species to meet changes in its environment. Therefore, SURVIVAL OF THE FITTEST was a response to a need to adapt to the environment.
• Darwin was interested in evolution in INDIVIDUALS and the process of selection that lead to the fittest variety and its subsequent survival.

-Darwin emphasized COMPETITION for sexual selection within populations as the driving force for evolution, whereas Wallace put more emphasis on the species meeting the demands of a change in their environment (ENVIRONMENTAL pressures forcing species to become adapted to their local conditions, leading populations in different locations to diverge)
Ex: China rarely have peanut allergies because the allele for peanut allergy is not common due to natural selection.
Ex: South and North have different people (Wallace)


Natural vs. Artificial Selection

Natural Selection: process in which environmental pressures result in the differential survival and reproduction of individuals of a population who vary in the details of shared, heritable traits.
o Natural selection is when a species adapts to its changing environment by choosing stronger traits that will improve their survival rate in future generations.
o Needs to be variation in traits, differential reproduction, heredity, end result (more of advantageous trait)
Ex: Finches with longer beaks were able to get more food than finches with smaller beaks. Therefore, longer beaked finches survived and reproduced, passing down their heritable traits to their offspring while the short beaked finches died off. In future generations, the population would have longer beaks

Artificial selection: process whereby HUMANS choose traits that they favour in a domestic species by SELECTIVE breeding.
o Humans purposely changing species natural traits to traits more desirable to us.
Ex: Crops. Farmer's breed tall plants together to produce more tall plants, leading to new populations that are tall and no short plants.


Summary of Darwin's Theory

-as population expands, resources are used by its individuals eventually become limited
-leads to competition
-individual has a form of a trait that makes it better suited to an environment -->
-better survival -->
-increased change of living long enough to produce offspring-->
-produce more offspring with the advantageous trait (frequency of that trait will tend to increase and become more common in the population over successive generations)


What is the Hardy-Weinberg Principle?

Hardy-Weinberg Principle (law of genetic equilibrium) provides a mathematical model for studying evolutionary changes in allelic frequency within a population.

• Hardy and Weinberg realized that under certain IDEAL conditions the frequency of an allele in a sexually reproducing population’s gene pool should remain stable from one generation to the next

• Stability is known as Genetic Equilibrium (theoretical state in which the population is not evolving), only occurs if the following conditions are met:

5 conditions
*If all of these conditions are met, the population will not evolve, as the allele frequencies will not change in future generations.
1. Mating must be random
2. Alleles cannot mutate - Any mutation in a particular gene would change the balance of alleles in the gene pool.
3. Immigration and emigration cannot happen à isolated population - no new alleles can come into the population, and no alleles can be lost (NO GENE FLOW). Both immigration and emigration can alter allelic frequency.
4. Large population - helps to ensure that chance alone does not disrupt genetic equilibrium (i.e. if a disturbing factor kills off a couple organisms, if will not affect the survival of the remaining as much if the population is large)
5. Natural selection cannot occur - no alleles are selected over other alleles. If selection occurs, those alleles that are selected for will become more common.

*Never occur in nature, so natural populations are never in genetic equilibrium, thus allele frequencies for any gene in a shared gene pool always tend to change.


What is the Hardy-Weinberg Principle Equation

To estimate the frequency of alleles in a population (following the Hardy-Weinberg Principle)

p + q = 1 (sum equal to 100%)

p = the frequency of the dominant allele
q = the frequency of the recessive allele

1 = p2 + 2pq + q2 →questions asking about homozygous or heterozygous

p2 = frequency of AA (homozygous dominant)

2pq = frequency of Aa (heterozygous)

q2 = frequency of aa (homozygous recessive)

-Identify which equation
-Identify which variable solving for
-if given numbers (i.e. 16 red birds out of 50 birds), must divide to see frequency.
-differentiate between homozygous, heterozygous and just dominant vs. recessive
-need to be a percentage/decimal!
-NEVER ASSUME (ex: 0.84 p2 + 2pq does not mean 0.84 dominant trait)


What prevents the populations from meeting 5 conditions stated in the Hardy-Weinberg Conditions?

External Disturbing Factors -->result in evolution of populations

Disturbing factors (genetic drift, bottleneck effect, and founder effect) forces a population to evolve in order to adapt and prevent populations from meeting the five conditions of a Hardy-Weinberg Principle


Genetic Drift

Genetic Drift: random change in allele frequencies in a population due to chance alone
• The RANDOM drift between phenotypes that can occur in a population
• Probability
• The larger the population, the smaller the impact of random changes in allele frequencies
• In each generation, some individuals may, just by chance, leave behind a few more descendents (and genes, of course!) than other individuals.
Ex: stepping on bugs (random selection)


Bottleneck Effect

Bottleneck: Drastic reduction in population size as a result of severe selection pressure (i.e. earthquake wipes out majority of population)
 A portion of the population is randomly eliminated resulting in a population that reflects the genetics of the survivors (new population are survivors)
 Decreases genetic variability
 Because so much of the genetic diversity is gone, the allelic frequencies change.
 There is an inaccurate sampling of the genes of the previous generation in the current generation.

I.e. island with blue, pink and red birds originally undergo bottleneck effect, resulting in the survival population having only blue and red birds


Founder Effect

Founder Effect: after a small group of individuals FOUND a new population, allele frequencies in the new population differ from those in the original population.
• The genetics of the population reflect those of the initial members that founded the new population
• New population may have:
o reduced genetic variation from the original population.
o a non-random sample of the genes in the original population.

Ex: blue, pink, red birds in original population. Most blue and red birds leave population to form new one, thus having more blue and red birds in new population.


Definitions of:
Allele Frequencies
Fixed Alleles

Allele Frequencies: abundance of a particular allele among the individuals of a population
-Proportion of an allele occurring within a population for a particular trait
-Microevolution is the change in allele frequencies in a population or species

Fixed alleles only have a single allele for a gene --> allele frequency is 100%
 All individuals in the population are homozygous for that trait
 Frequency for allele will not change unless mutation of other factor introduces new allele into the population


What are the basic mechanisms for evolution?
-causes of evolution

Basic Mechanisms for Evolution:
• Natural selection -->differential survival and reproduction
• Mutation -->give rise to new traits
• Migration/gene flow -->introduce new alleles
• Genetic Drift -->random change/shift in allele frequencies


Sources of Variation in Traits (genetic variation)

Genetic Differences

o Mutations →source of new alleles
o Crossing over at meiosis I →new combinations of alleles
o Independent assortment at meiosis I →mixes maternal and paternal chromosomes
o Fertilization →combines alleles from two parents
o Changes in chromosome number or structure →transposition, duplication, or loss of chromosomes


Collection of Evidence

3 types of evidence that helped prove Darwin’s theory of evolution
1. Palaeontology
2. Anatomy
3. Molecular Biology


How does fossilization occur?

o Species dies
o Flesh rots
o Bones broken down by other factors (i.e. animals)
o An organism or its traces become covered by sediments or volcanic ash
o Rain and other factors gradually wash in sand and gravel, burying remains
o Calcium replaced by minerals in deposit, turning bones to stone
o After a very long time, extreme pressure and mineralization transform the remains into rock
o Layers of sediments become layers of rock
o After millions of years, earth brings her remains closer to the surface
o Heavy rain erodes sediments, exposing fossil


Natural Selection Postulates/Principles

4 principles;
• Variations of phenotypes
• Heritability →heritable traits
• The Struggle for Existence
• Survival and Reproductive Rates →favourable traits are more likely to survive and reproduce

Natural selection postulates:
a) Individuals within a population vary in their traits (arises from mutations, genetic drift, gene flow, sexual reproduction-meiosis)
b). Some of these variable traits are heritable - passed onto offspring
c). More offspring are produced than can survive because of limited
resources such as food and nesting sites
d). Individuals with advantageous traits will survive and reproduce


Examples of Evidence of Evolution

Whale (how did they evolve from life on land to life in water?)

o i.e. Pakicetus skull →hypothesized resembled modern seal
o Found whale skeletons on land (Egypt, Pakistan) →Palaeontology (whales originated from land)
o Ex: Basilosaurus→another form of whale back in history
o Whales nowadays have front limbs that are similar/homologous structures with other species (i.e. humans and wolves) →anatomy (whales and humans evolved from a common ancestor)
o Fossils lead scientists to conclude that whales evolved from a land mammal called Sinonyx (4 legged). Inferred that the descendants found waters abundant with food and haven from competition→result of variation nd selection: front legs became fins→rear legs disappeared →bodies lost fur


Characteristics of Early Hominids

Possible hominin fossils date back as far as 7 million years ago
• Early hominids crawled on all fours and had smaller brains
• As humans evolved they became bipedal and developed larger brains
• As brain size increased capabilities increased, allowing humans to modify their environments to suit them best
• As human’s brain size increased, the species became more sophisticated
• Cultural trait of tool making (stone tools) →increase meat →larger brain size
Ex: Oldest ancestor: Orrorin tugenensis
First ancestor to use tools: Homo habilis
Recent ancestors: Homo erectus, Homo neanderthalensis, Homo floresiensis, Homo sapiens

Evidence from DNA
o Humans and chimps gene sequences are similar 98% identical
• Means that had a common ancestor only a few million years ago (recent)
• Therefore more changes/differences→evolved a common ancestor earlier in time→more time for differences to accumulate→distantly related


Hominid History


Hominid History:
• Found Hominid Footprints in Laetoli similar to human prints (at least 3.6 million years old)
• 1974 discovered skeleton of Lucy (Australopithecus afarensis)
o Could walk, but had lots of apelike features like the brain

•Homo erectus was the first to develop humanlike culture →made fires, handaxes (brain size of 900cc)

•Homo sapiens (modern humans; brain size of 1200-1600cc)

•Homo neanderthalensis had a brain size of over 1300cc, but is considered to have been much less sophisticated than, and possibly even driven to extinction by, modern humans.

•Human evolution began in Africa, and then migrated to all over the world. The evolution is inferred using molecular biology and fossils

•Scientists discovered that Neanderthals and humans did not interbreed due to the differences in DNA (Neanderthals had mitochondrial DNA)

Migration path:
• Australopithecines started off in east African
• Homo Erectus migrated to the rest of African as well as Europe and Asia
• Homo Neanderthals also migrated within African, Europe and Asia
• Homo Sapiens migrated to north and south America
• Overall, early hominids began in Africa and migrated until humans lived all over the world


Importance of Bipedalism and Brain Size

Importance of bipedalism
o Allows for travelling in larger distances, using hands for other usage, see further/clearly while traveling

Importance of Brain Size
o As brains increased in size, so did the ability of hominids to adapt to their environment
o Brain size increased over the generations
o Apes have brain size of 400-500cc


Apes vs. Humans

• C-shaped curve in backbone
• Flat foot with opposable big toe

• S-shaped curve in backbone
• Foot with arch, big toe aligned with other toes and not opposable
• Rounder skull, larger brain, flatter face with smaller jawbones and teeth

Lineage leading to humans had:
• Bipedal
• Manoeuvrable thumb
• Larger and more complex brain (improving ability to adapt and modify their environments)
• Longer period of postnatal development


What is Bipedalism?

• Bipedal: Adapted to habitually walking upright (2 legs)
• Humans evolved so that their knees could lock, their femurs slanted inwards and their big toes lined up with their other toes, allowing them to walk upright.

• Ability to move efficiently (energy efficient)
• Keeps body cooler
• Makes it easier to scan the horizon for predators
• Allow hands to gather food and carry it form place to place, make tools


Examples of Evolution In modern day

Antibiotic Resistance: example of evolution
• Antibiotics were created to kill or neutralize bacteria by interrupting cell wall synthesis or interfering with vital processes like protein synthesis, all while leaving human cells unharmed
• Natural selection creates antibiotic resistance bacteria
o Ex: medication, antibiotics, pesticides →form of artificial selection
• Evolution happens everyday Ex: microbes (bacteria, viruses, fungi etc.) keep evolving to survive inside the human being
• Some bacteria are resistant to drugs I.e TB in Russia ←example of natural selection
• Antibiotics kills most of bacteria, but some remain alive (resistant to antibiotics). These resistant antibiotics that survive multiply/reproduce ←genetic variety
o Bacteria undergo mutations and many of these mutations are harmful or useless but every now and then, one comes along that gives its organism an edge in the survival
o As the non-resistant bacteria are killed off, there is more room and resources for the resistant ones to thrive passing along only the mutated genes that helped them do so
• The strong bacteria reproduce and pass their traits to their offspring, creating a new fully resistant generation
• Reproduction isn’t the only way to do this; some can release their DNA upon death to be picked up by other bacteria.
• Others use a method called conjugation, connecting through pili to share their genes
• Over time, the resistant genes proliferate, creating entire strands of super resistant bacteria
• When the bacteria are fully resistant it poses a major threat to people in need them to treat infections.
• One of the main reasons for antibiotic resistance is the excessive use of antibiotics.
• If use too many antibiotics, then bacteria will become resistant. Therefore human survival depends on understanding of evolution
• Pesticides: pests with high tolerance for poison survive and reproduce more resistant pests. →pesticides are unable to control overpopulation of pests

Humans can use knowledge from evolution to protect endangered species, reduce evolution of microbes and minimize deleterious effects we have on the biosphere

How use understanding of evolution:
• Medicine: prevent development of resistance to antibiotics by bacteria, to insecticides by insect pests, to herbicides by weed species, etc.
• Monitoring mutations in pathogens (influenza virus)
• Alleles and disease resistance (some people are naturally resistant to plague diseases and HIV)
• Influencing disease frequency (adult onset diseases like Huntington’s)
• Slowing pesticide resistance


Collection of evidence with fossils called...

Palaeontology: evidence in form of fossils →stone-hard evidence of earlier forms of life.
o Consist of mineralized bones, teeth, shells, seeds, spores, footprints, feces etc. →information about body parts and organism’s activities
o Usually found in layers of sedimentary rock (Sandstone, shale)

oTraces of history and life from millions of years ago
oProvide information about when the fossil formed, depending on how deep the fossil is buried
oProvide information and understand geological changes about lives and relationships of organisms
oDocument environmental changes. Ex: if you find a marine fossil in your backyard you can know that it used to be part of a marine environment.
oShow how the anatomical features of species evolve over time

If a species has similar traits with a fossil, it proves that the species evolved from the fossil species

• Layers important in determining information about local and global events that were occurring as it formed, the age of the fossils and other clues
• Only a small proportion of organisms ever became fossils, many fossils lead to dead ends
• Older fossils are found below more recent geological layers in places where geological activity has not disturbed original orientation of layers. If two fossils are found in the same layer, it is assumed that they existed during the same time period
• Radiometric technique to determine age of fossils→decaying isotopes
Artifact: an object made by humans, typically an item of cultural or historical significance


Collection of Evidence with structures called...

• Anatomical evidence is in the form of physical features
• If two species have similar physical features (homologous structures), they evolved from a common ancestor
o Homologous structures: structure similar among related organisms because those organisms have all descended from a common ancestor that had that equivalent trait

• Ex. The front fin of a whale has homologous structures with the front limbs of other species including humans and wolves. This proves that whales, humans and wolves evolved from a common ancestor.


Collection of Evidence with sequences on a molecular level called...

3. Molecular Biology
• Molecular biologists are able to determine and compare DNA base sequences and the amino acid sequences of the same proteins form different animals

• The less closely related two species are, the more differences there are in their DNA or amino acid sequences because there would have been more time for mutations to accumulate
• On the other hand, the more closely related two species are, the fewer differences there are

• Ex. The current DNA studies suggest that whales are most closely related to hippopotamuses
• Ex. The DNA sequences between chimps and humans are 98% similar, meaning that they had a recent common ancestor



Mutation: permanent change in the nucleotide sequence of DNA

• The sequences of the four chemical building blocks of DNA (A,C,T,G) determine the traits of all living things.

o Mutations are random →beneficial, harmful, neutral
o Lethal →can contribute to evolution
o Neutral →no affect to natural selection (but can cause evolution in different environments)
o Beneficial →contributes to evolution (leads to adaptive traits that favour survival)

o Not all mutations matter to evolution
o Ex: mutation could die out and not get passed down

o Give rise to variations in traits
o i.e. structural, functional, or behavioural alterations →threaten survival (lethal mutation)
o Neutral mutation changes the base sequence in DNA, but the alteration has no effect on survival or reproduction (neutral)
o Traits can be advantageous that allow for differential survival and reproduction. This results in a higher chance of survival and reproduction, leading to future generations having the mutation.
o Give rise to Earth’s staggering biodiversity
o Mutations are significant to evolutionary change because they allow specie’s DNA to change, which changes their traits and thus causes a whole new species to evolve.

• DNA fails to copy accurately
• External influences i.e. exposure to chemicals, radiation



Adaptations: organisms shaped to enhance their survival and reproduction. An adaptive trait a heritable trait that enhances an individual’s fitness in a particular environment. The adaptive trait is maintained and evolved by means of natural selection. Ex: Finches adapted to food specifically on each island

• A feature that is common in a population because it provides some improved function
• Overtime, individuals with the most adaptive traits tend to survive longer and reproduce more than their less fit rivals
• Natural selection →leads to Adaptations →evolution
o Natural selection is where organisms with the adaptive traits survive better than organisms without the trait


Why is evolution referring to when populations evolve and not individuals?

Evolution occurs on the scale of a population. A change in one individual who does not pass on the gene will not make a difference. Therefore evolution must cause a change in the line of descent (must pass down traits).

Ex: Lethal mutation in one individual will cause the individual to die (not pass down-->no evolution)