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Evolution:
Adaptations & Variations:
Adaptation : A structure , behaviour or physiological process that helps an organism survive and reproduce in its environment.
Examples: Camouflage : allows organisms to almost be invisible to predators
- Migration : allows organisms to move in large groups to relocate to find food, they are more protected from predators when travelling in large groups;
- Hibernation : allows organisms to reduce their metabolism to save energy
- Mimicry Is a unique structural adaptation where a harmless species resembles a harmful species in coloration or structure
Adaptations are the result of gradual, accumulative changes that help an organism survive and reproduce. These changes are the result of random, heritable mutations in DNA that gathers over generations.
Variations are structural, functional, or physiological differences between individuals within a population that occur by genetic mutation (not all variations = adaptations).
How Do Adaptations Develop?
- A random mutation causes a new trait ( variation ).
- Variation is created by the different combinations of genetic information (alleles) that offspring inherit from their parents
- The different allele combinations result in different Phenotypes and Genotypes
- Variations can be structural (e.g., beak shape), functional (e.g., how an organ works) or physiological (e.g., ability to digest certain foods) differences between individuals
- As a variation becomes more common , it will be considered to be a trait or a characteristic of the population
- Variation → The raw material for natural selection
- Adaptations can be positive or negative depending on the environment and what is favoured
- Helpful variations increase chances of survival and, therefor,e reproduction
- Environmental conditions determine whether a variation will become an adaptation
- Example: Peppered Moths
How Do Adaptations Develop? (Simplified)
- Adaptations develop through random mutations in DNA, which create variation.
- These variations can be helpful, harmful, or have no effect.
- If a variation is helpful, it gives a selective advantage — improving the organism’s chances of survival and reproduction.
- Over time, through the process of Natural Selection, individuals with helpful traits( selective advantage that process) survive and reproduce more than others. This results in the helpful traits become common in the population. This leads to the development of an adaptation.
Sources Of Variation:
- Sexual Reproduction: “Fitness” Is the ability of an organism to reproduce successfully. - Crossing over during meiosis - Independent assortment - Random fertilization of egg/sperm
- Mutations: A mutation is a permanent change in the genetic material of an organism and is the only source of new genetic variation and alleles.
Mutations can be: a) Neutral - No immediate effect on an individual's fitness. b) Harmful - Reduces an individual’s fitness; can cause cells to die, malfunction or even become cancerous (causing them to multiply rapidly) c) Beneficial - Increases an individual's fitness; may allow for a selective advantage , allowing an organism to be more likely to survive and reproduce.
Selective Advantage:
- A genetic advantage that improves an organism’s chances of survival in terms of both survival in a changing environment and reproduction.
- This advantage arises from a mutation that has become beneficial , even if it was a disadvantage at first.
Selective Advantage Example:
The English Peppered Moth: Variation to Adaptation.
- Two variations: light-colored moths and dark-colored moths
- Before industrialization : light moths had advantage (blended with light trees -> light-coloured lichen.) Uses Camouflage , More population, fewer were targeted.
- After industrialization : trees became dark due to soot.
- Dark moths now had the selective advantage (blended in, avoided predators.
- In 50 years, 95% of moths in Manchester were dark-colored
- Shows how environmental changes can lead to adaptation through natural selection
Medicine and Resistance:
- Bacteria can cause infection when they multiply to form large numbers.
- Pathogenic bacteria cause disease and they require ideal conditions for reproduction.
- Antibiotics are used to prevent bacterial reproduction by killing them before they divide.
Problems with Antibiotics:
Antibiotic resistance:
- Antibiotics are specific to certain bacteria.
- Over time, bacteria can evolve new strains (species)
- This happens when a mutation occurs in their DNA , which gives them a trait that resists the effects of current antibiotics. - Simple Terms: Some bacteria have a mutation that makes them resistant.
- It takes a lot of research and money to find antibiotics that work.
Artificial Selection and Food Crops: ● Farmers grew many common crops from wild mustard by choosing plants with traits they liked. ● They let only those plants grow and make seeds. Over time, this changed the plants — they evolved too quickly. ● We breed food crops to increase their nutritional value and crop amount. ● We also grow them to survive dry weather or fight off bugs.
Consequences Of Artificial Selection: ● Other traits may be negatively affected. ● For example, English bulldogs are bred to have flat faces, but, as a result, many of the breed suffer from respiratory problems ● Decreases genetic diversity in a population, which makes the population less fit for environmental changes and natural selection. ● Monoculture means growing one type of crop over a large area. ● It's risky because if a new bug or disease comes, it can harm or kill all the plants since they're so alike.
Natural Selection VS Selective Advantage:
Natural Selection
● A process where individuals with helpful traits survive and reproduce more than others. ● Over time, these helpful traits become common in the population. ● It's how adaptations develop. ● Think of it as the overall process that shapes evolution.
Selective Advantage
● A specific trait or variation that gives an organism a better chance to survive and reproduce. ● It is the reason why natural selection happens — nature “selects” that advantage. ● Think of it as the beneficial trait that helps an organism.
In Short:
● Natural Selection = the process ● Selective Advantage = the beneficial trait in that process
Important Questions:
Why is genetic variation important in natural selection?
- It provides the different traits that natural selection can act upon.
- This allows some individuals to survive and reproduce better than others.
How do selection pressures influence gene frequency in a population?
- Selection pressures favour certain traits.
- Increases the survival and reproduction of individuals with advantageous genes.
- The frequency of these genes increases in the population over time.
What is the role of natural selection in evolution? It increases the frequency of advantageous genes, leading to better adaptation and potentially the formation of new species.
Define natural selection: Natural selection is the process where individuals with traits that help them survive and reproduce are more likely to pass on those traits to the next generation.
Contributions To The Theory Of Evolution:
1. Charles Lyell: ● Proposed theory of Uniformitarianism - The same natural forces shaping Earth today also shaped it in the past — the present helps us understand the past. ● Geological processes at uniform rates build & wear down Earth’s crust. ● One of the first to propose that the Earth was millions of years old instead of a few thousand years old.
Principles of Geology: Principles of Geology, published by Lyell just before the Beagle set sail, was read by Charles Darwin. ● Explained geological processes that shaped the earth ● Helped Darwin understand sea shells in the Andes mountains at 12,000+ feet above sea level. ○ Expanded Earth’s age
2. Jean-Baptiste Lamarck: ● Jean-Baptiste Lamarck, 1809. ● One of the first scientists to understand that change occurs over time. ● Stated that changes are adaptations to the environment acquired in an organism’s lifetime. ○ Proposed these changes were passed to the offspring
Lamarck’s Idea of Evolution: The idea is called the Law of Use and Disuse ● If a body part were used, it got stronger ● If body part NOT used, it deteriorates ( worsens) ● Use & Disuse - organisms could change the size or shape of organs by using them or not using them
Examples: ● Blacksmiths and their sons (muscular arms) ● Giraffes’ necks became longer (from stretching for food) ● Snakes’ legs shrank because they were not using them.
Lamarck’s Mistakes: ● Lamarck did NOT know how traits are inherited (traits are passed through genes- not common knowledge during his time). ● Genes are not changed by activities in life. ● Change in genes is through mutation that occurs before an organism is born.
Lamarck’s Contributions: Lamarck is credited towards today’s modern theory of evolution because he acknowledged that the environment plays a role.
● Lamarck proposed that evolution was a constant process of striving toward greater complexity and perfection. ● Even though this belief eventually gave way to Darwin's theory of natural selection , Darwin disagreed that evolution strived for perfection. ● Darwin concluded that evolution was based on random variation , rather than striving towards a goal (perfection).
3. Thomas Malthus: ● Thomas Malthus, 1798 ● Economist ● Observed babies being born faster than people were dying. ● Population size is limited by resources such as the food supply
Population Transition:
● Malthus reasoned that if the human population continued to grow unchecked , sooner or later, there would be insufficient living space & food for everyone. ● The death rate will increase to balance the population size & food supply ● Darwin realized Malthus’ principles were visible in nature. ● Plants & animals produce far more offspring than can be supported. ○ Most offspring die ; otherwise, the earth would be overpopulated.
The Galapagos Islands: ● Group of 16 Islands 1000 km (621 miles) west of South America, part of Ecuador. ● The Galapagos Islands are named after the unique giant tortoises that live there. ● Slightly varying climate among the islands.
Darwin’s Observations (Continued): ● Left unchecked, the number of organisms of each species will increase exponentially , generation to generation. ● In nature, populations tend to remain stable in size. ● Environmental resources are limited. ● Individuals of a population vary extensively in their characteristics with no two individuals being exactly alike. ● Much of this variation between individuals is inheritable.
Darwin’s Conclusion: ● Production of more individuals than can be supported by the environment leads to a struggle for existence among individuals. ● Only a fraction of offspring survive each generation. ● Survival of the Fittest - Individuals who inherit characteristics most fit for their environment are likely to leave more offspring than less fit individuals.
Darwin’s Evolutional Theory of Natural Selection: What is natural selection? Individuals who have physical or behavioural traits that better suit their environment are more likely to survive and will reproduce more successfully than those that do not have such traits. ● Survival of the fittest Acts on a range of phenotypes in a population. NOT Individuals!!!!!!!!! (Population: all members of a species that live in an area.)
What is Evolution? Evolution occurs as a population’s genes and frequencies change over time! ● Creating new phenotypes
Gene Pool - All the alleles in a population The frequency of a specific allele is called allelic frequency (how often it appears).
What can cause genetic changes in populations?
- Mutations
- Environmental changes (Natural selection)
- Genetic Drift
- Gene Flow
- Non-random mating sexual selection
Examples: ● Reproductive isolation- when populations can't breed due to geographic separation ● Gradualism - gradual change in an environment over a long period of time, leading to new species
Adaptation: ● An adaptation is an inherited characteristic that increases an organism’s chance for survival. ● How adapted a population is to its environment depends on how common the adaptation is. ● Adaptations can be: ➢ Physical: Speed, camouflage, claws, quills, etc. ➢ Behavioural: Solitary, herds, packs, nocturnal, activity, etc. ● Individuals do not get to pick and choose their adaptations. ● Adaptations are qualities already present among some individuals in a population (luck of the draw). ● If the adaptations are favourable, they become more common in a population.
Divergence :
Divergence is when two groups of the same species slowly become so different that they can’t mate anymore. This can lead to a new species forming.
Yet, the common ancestor remains (descent with modification).
Speciation:
The formation of a new species= speciation. ● Divergence is the driving force behind speciation. ● Species can have subspecies; ● EXAMPLE: All dogs are the same species (Canis familiaris). Due to artificial selection, they are very different (Great Dane vs. Chihuahua) thus resulting in subspecies. ● Subspecies - members of the same species that differ genetically. Could potentially lead to a new species.
Two Models of Evolution:
- Gradualism : a model or hypothesis of evolution in which gradual change occurs over a long period of time.
- Punctuated Equilibrium : a model of evolution in which periods of rapid change in species are separated by periods of little or no change.
Evolutionary Time Scales:
● Macroevolution : Long time scale events that create and destroy species. ● Microevolution : Short time scale events (generation-to-genera tion) that change the genotypes and phenotypes of populations
Evidence for Evolution:
- Embryonic Development
- Microevolution ( Biographical)
- Body Structures
- Biological Molecules
- The Fossil Record
Microevolution: ● Evolution that we can see in action during a small amount of time, within generations ● Examples include peppered moths, antibiotic resistance, pesticide resistance in insects.
Biological Molecules:
Similarities in DNA sequences-
● The more alike two organisms are, the more amino acids they have in common (genetic sequence). ● Example- Chimpanzees and humans share a nearly identical amino acid sequence. ● The idea is simple: the more alike two organisms are, the more alike their DNA is (and vice versa).
Homologous Body Structures:
● Related structures that are inherited from a common ancestor. ○ Structures have different mature forms but develop from the same embryonic tissues. ● Provide strong evidence that all four-limbed animals with backbones descended, with modification, from a common ancestor. ● Scientists noticed animals with backbones (vertebrates) had similar bone structure ● Structures may differ in form or function ; however they develop in similar patterns ○ Arms, wings, legs, flippers
Vestigial Structures:
● Structures that are present in an organism, but serve no apparent purpose. ● Examples: appendix in man, legs on snakes, pelvic bone of whales.
Similarities in Early Development:
● Embryonic structures of different species show significant similarities ● Embryo – early stages of vertebrate development
Evidence for Evolution - Comparative Embryology
Mechanism of Evolution:
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SBI3U Mechanisms of Evolution
Review What are the 5 sources of evidence that support evolution? For each one, provide an example. What is a vestigial feature? What is the difference between a homologous and analogous feature?
More Review Genetic variation arises from:
Sexual reproduction : each individual inherits a new combination of alleles therefore, each new generation is made up of genetically unique individuals
Mutation : new mutations happen RANDOMLY in each generation, allowing new traits to develop
Genetic variation in a population occurs randomly, but natural selection acts upon that variation in a non random way
Genes
Individuals with genes that help them survive will reproduce pass along those genes to offspring increase the percentage of those genes in the population
Natural Selection acts on Populations
Individual organisms DO NOT evolve, populations do Must observe the changes that occur within populations
Population : a group of individuals of the same species in a specific area at a specific time
Gene pool : all genes of all the individuals in a population the percent of each allele of any given gene present in the population the genetic characteristics of that population
Factors that change allele frequencies in populations
● Mutation ● Gene flow ● Non-random mating ● Genetic drift ● Natural selection
Mutation A change that occurs in the DNA of an individual Heritable mutation could affect an entire gene pool Greater genetic variation in a population greater diversity greater chance of a selective advantage to some individuals in a changing environments.
Gene Flow The net movement of alleles from one population to another as a result of migration Genetic information can be exchanged between individuals of different populations through gene flow Greater genetic diversity may help the population to survive
Example There are two populations of wolves:
Population A lives in Canada Population B lives in the northern United States
For many years, these groups are separated. But then, a few wolves from Canada migrate south and join the U.S. wolf pack. They mate with local wolves, introducing new genes into the U.S. population (like stronger winter fur or different hunting behavior).
This mixing of genes between the two populations is an example of gene flow.
