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Evolution process

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Biology

Through evolution, populations can adapt to suit their environmental conditions. Thus, evolution is essential for the survival of all living organisms.

Evolution: the change in the heritable characteristics of populations over several generations

Speciation: the evolutionary process by which populations evolve to become different species.

How does evolution occur?

Individuals in populations possess a variety of characteristics that are a result of the interaction between their genes and the environment. Differences in the characteristics of the population come about due to both genetic and environmental sources of variation, with mutations being the ultimate source of all genetic variation.

Mutation: A gene mutation is a change in the sequence of base pairs in a DNA molecule that may result in an altered polypeptide.

Because each individual possesses slightly different traits, it follows that each individual has a slightly different level of fitness relative to the environment.

For instance, in a population of Arctic foxes, individuals with the whitest fur will be better able to blend in against the snow, resulting in a lower risk of predation. This means more of these individuals will be able to survive and breed, and thus have higher fitness.

Evolution arctic fox StudySmarter

Figure 1. Arctic Fox blending in with its habitat. Source: Freepik.com

Evolution acts upon this variation in observable traits. Different evolutionary processes, such as natural selection, sexual selection, and genetic drift, act upon the variation in the population, resulting in some traits becoming more common and others more infrequent.

As a result, over time, populations become fitter and better suited to their environment. As populations become more and more specialised for their specific environments, they might become distinct species that can no longer interbreed with one another in a process known as speciation.

DNA → Mutations → Change in genotype → Changes in phenotype → Variability in populations (adaptations) → Changes in allele frequency in the gene pool → New species → either evolution (continued success in the environment) or extinction (overwhelmed by environmental pressures)

All life on Earth shares a common ancestor known as the Last Universal Common Ancestor (LUCA) who lived about 3.5-3.6 billion years ago; however, billions of years of evolution and speciation has resulted in the incredible diversity of life that we can observe today.

Who is the father of evolution?

The theory of evolution by natural selection is largely credited to Charles Darwin. He discussed it in his book "On The Origin of Species", although it was also conceived independently by Alfred Russel Wallace.

Darwin based this theory on several observations:

  • Firstly, observable traits such as morphology, physiology, and behaviour vary among individuals. In other words, there is phenotypic variation within populations.

  • These varying traits confer differential fitness, which means they lead to different levels of success in terms of survival and reproduction.

  • Finally, traits are heritable, which means that they are passed down from parent to offspring.

Darwin argued that members of a population are more likely to be replaced by offspring of parents who have favourable traits and are better able to survive and reproduce. As time goes on, populations gradually change to become better suited to their environments.

What is the evidence for evolution?

There is overwhelming evidence that the theory of evolution is true. Let’s go over a few examples:

The genetic code

Firstly, the structure of the genetic code is very similar for all organisms on earth. Our DNA is composed of the same nitrogenous bases - A, C, T and G - and we share a significant proportion of our DNA with our closest taxonomic relatives. The closer one species is to another, the more similar their genetic information tends to be.

The fossil record

Next, we have an extensive fossil record of the organisms that used to live on Earth but have gone extinct. By studying fossils, we have been able to infer what life used to look like on Earth and understand more about how life evolved and diversified. Of course, the fossil record is not complete. The way fossils are formed means that soft-bodied organisms may not be accurately represented in our records. There are also many intermediate forms between kinds of organisms that we have not discovered yet or that were not fossilised at all.

Selective breeding

There are also many examples of plants and animals whose evolution has been guided by humans through selective breeding, including dogs, domesticated farm animals, and agricultural crops. Darwin used selective breeding as strong evidence for evolution - in this case, through artificial selection, when he first introduced his theory to the public.

Real-time evolution

Finally, we can observe evolution happening in real-time. For example, fast-evolving organisms such as bacteria continue to evolve and adapt to the antibiotics we use against them. There are now many strains of ‘superbug’ that have adapted to resist antimicrobial compounds and will be able to survive heavy doses of medicine.

What are the types of evolution?

There are several terms used to describe patterns in which the process of evolution occurs in different organisms. Examples of these include:

  • Divergent evolution

  • Convergent evolution

  • Parallel evolution

Evolution Different types of evolution StudySmarter

Figure 2. Different types of evolution. Source: Finty Royle - StudySmarter Originals.

What is divergent evolution?

Divergent evolution refers to the process by which groups descended from the same common ancestor accumulate genetic differences, which ultimately leads to speciation. This might occur as a response to changes in the environments of the two groups, such as changes in the abiotic conditions or the introduction of new biotic interactions.

What is convergent evolution?

Convergent evolution is the process by which groups that are not closely related - that is, they are not descended from the same direct ancestors - independently evolve similar features in response to similar selection pressures. In other words, through convergent evolution, different groups separately arrive at the same solution to similar problems. For instance, birds, flying insects, and flying mammals have all arrived at the convergent phenotype of wings as a ‘solution’ to the ‘problem’ of mobility. There is no one close common ancestor for all of these winged animals. Indeed, the anatomy of wings looks very different from group to group; however, most wings operate based on the same principles due to flight physics.

What is parallel evolution?

Parallel evolution refers to the process by which two groups sharing a similar trait, evolve another trait in a similar environment.

To understand how this might occur, let’s imagine two groups of similar plants that are in different locations but are exposed to very similar environmental conditions. Because they are dealing with the same conditions, they might evolve similar adaptations completely independently from one another. For instance, if they were in an arid environment, they might develop a waxy cuticle and stems that can store water.

Parallel evolution is often confused with convergent evolution. The important thing to keep in mind here is that in convergent evolution, two groups arrive at the same phenotype from different starting points, while in parallel evolution both groups come from similar starting points.

Population in Ecosystems - Key takeaways

  • Evolution is defined as the change in the heritable characteristics of populations over several generations.

  • Different evolutionary processes act upon the variation in the population, resulting in favourable traits becoming more common and unfavourable traits more infrequent.

  • There are several patterns in which evolution can occur between different groups, including divergent evolution, convergent evolution, and parallel evolution.

  • The theory of evolution by natural selection is credited to Charles Darwin, although AR Wallace also developed it independently.

  • There is a lot of evidence for evolution, including the fossil record, the universal genetic code, and evolution occurring in real-time today.

Evolution process

 There are several patterns by which evolution occurs. Examples of them are divergent evolution, convergent evolution, and parallel evolution.

The theory of evolution by natural selection is a scientific theory that is substantiated by empirical evidence. In science, a theory is defined as a plausible or scientifically acceptable principle used to explain phenomena. In order to become widely accepted, theories must be substantiated with evidence that is obtained in a rational and methodical manner. Scientific theories are reliable and rigorous and are not to be confused with the colloquial usage of the word theory to refer to speculation and unproven ideas.

Charles Darwin is credited as the scientist who first offered the theory of evolution by natural selection.

Mutations

The change in the heritable characteristics of populations over several generations

 In convergent evolution, two groups arrive at the same phenotype from different starting points, while in parallel evolution both groups sharing a similar trait, evolve another trait in a similar environment. 

On the Origin of Species

change, heritable, several generations

There is genetic variation within populations.

Last Universal Common Ancestor

Convergent evolution

Convergent evolution

Parallel evolution

Divergent evolution

Any two of: the universal genetic code, the fossil record, artificial selection through selective breeding, the evolution of microorganisms in real-time.

A, C, T and G (or Adenine, Cytosine, Thymine, and Guanine).

Final Evolution process Quiz

Question

Evolution is defined as the _____ in the _______ characteristics of populations over ________ ____________.



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change, heritable, several generations



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Question

Which of the following is not one of Darwin’s original observations that led him to develop the theory of evolution by natural selection?

  • There is phenotypic variation within populations.

  • These varying traits confer differential fitness.

  • Traits are heritable.

  • There is genetic variation within populations.

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Answer

There is genetic variation within populations.

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Who discovered evolution?

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Charles Darwin and Alfred Russell Wallace



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Name the book in which Charles Darwin first introduced his ideas about evolution through natural selection.



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 On the Origin of Species



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What does LUCA stand for?



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Last Universal Common Ancestor



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When did LUCA live on Earth?


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3.5-3.6 billion years ago



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What is the difference between convergent and parallel evolution?



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In convergent evolution, two groups arrive at the same phenotype from different starting points, while in parallel evolution both groups come from similar starting points.



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Give two examples of evidence of evolution.


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Any two of: the universal genetic code, the fossil record, artificial selection through selective breeding, the evolution of microorganisms in real-time 



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What are the four nitrogenous bases that comprise the DNA of most organisms on Earth?


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A, C, T and G (or Adenine, Cytosine, Thymine, and Guanine)



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What is divergent evolution?

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Divergent evolution refers to the process by which groups descended from the same common ancestor accumulate genetic differences, which ultimately leads to speciation.

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What is convergent evolution?

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Convergent evolution is the process by which groups that are not closely related - that is, they are not descended from the same ancestors - independently evolve similar features in response to similar selection pressures.

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What is parallel evolution?

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Parallel evolution refers to the process by which two groups independently evolve a trait in separate environments that share a similar original trait.

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How is evolution different from speciation?

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speciation is an evolutionary process by which populations evolve to become different species whereas evolution is the change in the heritable characteristics of populations over several generations. 



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What is the definition of evolution?

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Evolution is defined as the change in the heritable characteristics of populations over several generations.

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Give three examples of different evolutionary processes.

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Answer

natural selection, sexual selection, and genetic drift

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What are the two sources of variation in a population?

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Answer

Genetic and environmental.

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What is the primary source of variation?

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Mutations.

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What are the three sources of genetic variation?

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Mutations, crossing over, and independent assortment.

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A ______ is a change in the DNA base sequence that results in the generation of one or more new alleles.

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Answer

Mutation

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Crossing-over occurs when ______ chromatids exchange alleles during meiosis.

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Answer

non-sister

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The presence of an allele on one gamete will not affect its chances of fusion with any other allele.

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True

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What is the formula for the number of possible chromosome combinations due to independent assortment?

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2n, where n is the number of chromosomes in a haploid cell.

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What does it mean when a trait is polygenous?

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Answer

Multiple genes control it.

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Are genetic or environmental factors best represented by a bell curve?

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Environmental

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_________ factors have discrete phenotypes

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Genetic

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Discrete data is best represented by a _________

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bar chart.

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Can environmental influences on phenotype be passed on to offspring?  

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Variation in phenotype due to environmental factors does not usually cause genetic variation, and because of this, it cannot be passed on to offspring. For instance, something like the presence or absence of nitrogen in an environment does not cause an individual to mutate a new allele that allows it to survive better in those conditions.

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What are the environmental sources of variation?

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  • Climate (temperature, rainfall, sunlight.)
  • Food availability (or resources such as nitrogen.)
  • Presence of predators.

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What is a mutation?

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Answer

A change in the DNA base sequence that results in the generation of one or more new alleles.

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Question

Natural selection is the _____________ and ________ of individuals due to differences in their _________.



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Answer

differential survival; reproduction; phenotype



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These are environmental factors that affect an individual’s chances of survival.

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Answer

Selection pressures



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 _______ is an organism’s ability to survive and pass its genes on to its offspring.


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Answer

Fitness

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_______ is crucial for natural selection to act upon. Small populations have _____ variation than big populations.



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Answer

variation; less

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True or false. When a population’s dominant phenotype changes, the population has evolved.



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false

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Give two reasons why smaller populations are more vulnerable to extinction.



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  • Smaller populations have less variation

  • Genetic drift

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Genetic _____ is the gradual change in allele frequencies in a small population due to chance, rather than natural selection.



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drift

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True or false. Speciation occurs through evolution. 



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true

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Question

An imaginary population of moths has two morphs: early emergers, whose caterpillars hatch in July, and late emergers, whose caterpillars hatch in September. These caterpillars only feed on one species of flowering plant.


Suppose that historically, the plants are most abundant in July-August. Predict which moth morph is more likely to dominate in the population.



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Answer

Early emergers

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Question

An imaginary population of moths has two morphs: early emergers, whose caterpillars hatch in July, and late emergers, whose caterpillars hatch in September. These caterpillars only feed on one species of flowering plant.


Due to climate change, the host plant’s flowering cycle is starting later in the year. Predict which moth morph will dominate the population in the future.



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Answer

Late emergers

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________ selection selects for the average phenotypes and against more extreme phenotypes.

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Stabilising

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 ________ selection favours one extreme phenotype and usually occurs when changes in the environment shift the optimum phenotype to the left or right of the original value.

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Directional

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________ selection, also known as diversifying selection, favours extreme phenotypes rather than intermediate phenotypes, and is the least common form of selection.

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Disruptive

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What is polymorphism?


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Polymorphism is the existance of several phenotypes in a population. It occurs when there are many genetically distinct forms (morphs) of a species that still interbreed in the same population.

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Which morph of the peppered moth was most abundant in industrial England?


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The melanic morph

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Suggest which form of selection best describes the following statement.


Polar bears with a birth weight of less than 0.4kg have a significantly lower survival rate.

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Directional selection

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Suggest which form of selection best describes the following statement.


This type of selection is involved in speciation.

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Divergent selection

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Suggest which form of selection best describes the following statement.


Grey moths are less successful than white or black moths.

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Divergent selection

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Suggest which form of selection best describes the following statement.


Pangolins with longer tongues are able to forage more effectively.

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Directional selection

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What is natural selection?

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The differential survival and reproduction of individuals due to differences in their phenotype.

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Why is genetic variation important?


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Because without genetic variation, a population wouldn't be able to evolve in response to the changing environment and, as a result, may have increased risk of extinction.

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