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Biological Evolution

Grade 6 Science Worksheets

Evolution is the gradual accumulation of small genetic variations that causes species of living organisms to change over time. The fundamental concept that underpins the study of biology and the diversity of life on Earth is evolution.

Table of Contents:

  • Natural Selection
  • Genetic Drift
  • Evolution and Adaptation
  • Differential Reproductive Success
  • Mutation
  • Hardy-Weinberg principle
  • FAQs
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The theory of evolution by natural selection, proposed in the mid-nineteenth century by Charles Darwin and Alfred Russel Wallace, states that evolution occurs as a result of the interaction of three factors: variation, inheritance, and selection. Trait variation exists within organism populations, and some of these variations are passed down from generation to generation via inheritance.

Selection refers to the fact that some people are more likely than others to survive and reproduce and that those who are more adaptable to their surroundings are much more susceptible to passing their genes on to the next generation. This selection procedure can result in the evolution of new species over many generations.

The theory of evolution is supported by a large body of evidence from many different fields of science, such as genetics, paleontology, comparative anatomy, and biogeography. The theory of evolution is widely accepted by scientists and is regarded as one of the most well-established scientific concepts in existence.

Natural Selection

Natural selection is the process through which certain traits are becoming more or less prevalent in a population over time due to individuals with some of those traits surviving and reproducing. Individuals with better-suited traits to their ecosystem are more likely to live and reproduce, passing on those traits to their offspring. This can result in the emergence of new species over time.

Natural selection was first proposed in the mid-nineteenth century by Charles Darwin and Alfred Russel Wallace. While monitoring the life diversity on the Galápagos Islands and elsewhere, Darwin and Wallace completely separately developed the concept.

The evolution of the beaks of Darwin’s finches, a group of closely connected bird species found on the Galápagos Islands, is an example of natural selection. Different finch species evolved different-looking beaks that are modified to various food sources over time.

Some species, for example, have long, thin beaks for eating bugs, while others have short, thick beaks for busting nuts. Natural selection has resulted in these differences in beak shape: finches only with the best-suited beaks for their food sources are more likely to live and reproduce, passing on their favorable characteristics to their offspring.


Genetic Drift

Genetic drift is an evolutionary mechanism characterized by random fluctuations in the number of alleles (gene versions) in a group over time. Unlike natural selection, which is based on the theory that only certain traits provide a survival benefit, genetic drift is the result of chance events that cause changes in a population’s genetic makeup.

Because unpredictable events such as mutation, migration, and genetic drift can have a disproportionate effect in small populations, genetic drift can have a considerable influence on the frequency of alleles. For example, if an inhabitant of only a few individual people is separated from the rest of its own species, possible events can cause the population to lose certain alleles over time.

The founder effect, which occurs whenever a small number of people becomes secluded from such a greater population and creates a new population elsewhere, is yet another example of genetic drift. Due to the random loss of certain alleles during the founding process, the genetic makeup of the new population will differ from that of the original population.

In general, genetic drift is more prominent in tiny populations and becomes less pronounced as population size increases. The effects of genetic drift in large populations are frequently outweighed by the effects of natural selection, which could also lead to something like the evolution of new species over time.

Evolution and Adaptation

In biology, evolution and adaptation are concepts that are related. The procedure by which species of living organisms evolve over time because of the gradual accumulation of small genetic variations is referred to as evolution. The process through which a species becomes best suited to its surroundings through the formation of variations in its traits over time is referred to as adaptation.

Evolution produces adaptation. Natural selection causes organisms to become better adapted to their environment as they evolve. People with traits that really are best suited to their environment are favored by natural selection, and all these characteristics are more likely to be passed down to the next generation. This results in the emergence of new lifeforms that are better adapted to their surroundings over time.

Adaptation can be seen in a wide range of species, from chameleon camouflage to cacti’s ability to store water in their leaves. Physical adaptations, such as changes in anatomy or physiology, and behavioral adaptations, such as changes in behavior or habits, are two examples of adaptations.

Differential Reproductive Success

Differential reproductive success refers to individuals’ unequal success in reproducing and having to pass on their genes to the next generation. As the driving force behind species evolution, this idea is a crucial component of the natural selection theory of evolution. selection.

Differential reproductive success occurs when some individuals in a population outperform others in terms of reproduction. This can be due to a number of factors, such as physical characteristics, behavior, or environmental conditions. Individuals with a physical trait that allows them to better escape predators or find food, for example, are more likely to survive and breed than individuals without that trait.

As a result, that individual’s characteristics are more likely to be passed down to the next generation, and the prevalence of those characteristics in the population will rise over time.

Differential reproductive success leads to species evolution over time in this way. As individuals with advantageous traits become more prevalent in a population, the population evolves and becomes more adapted to its surroundings. Natural selection is responsible for the diversity of life on Earth, as well as the phenomenal adaptations that species have developed over time to thrive and survive in their environments.


Genetic mutations are changes to an organism’s genome’s DNA sequence. Mutations can occur naturally as a result of DNA replication errors or as a result of exposure to environmental factors such as radiation or chemicals.

Mutations can have a wide range of effects on an organism, ranging from completely harmless and having no effect to being harmful and potentially fatal. Some mutations can result in the development of new traits or abilities that give a survival advantage, whereas others can result in genetic disorders.

Mutations play an important role in the evolution process. Mutations provide the raw material for natural selection to act on by introducing new genetic variation into a population.

Beneficial mutations that provide a survival advantage will become more common in a population over time because those individuals are more likely to survive and reproduce. Natural selection results in the evolution of new species and the development of new adaptations.

Genetic mutations are a source of genetic variation that plays an important role in the evolution process by providing raw material for natural selection to act on. While some mutations can be harmful, others can be advantageous, resulting in the evolution of new species and adaptations over time.

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Convergent Evolution

This is when two different species evolve similar traits independently of each other, usually because they live in similar environments and face similar selective pressures. For example, both sharks and dolphins have evolved streamlined bodies and fins for efficient swimming, even though they are not closely related, and evolved these traits separately.

Divergent Evolution

This is when a single species evolves into multiple distinct species over time, usually because different populations become isolated from each other and adapt to different environments. For example, Darwin’s finches on the Galapagos Islands evolved different beak shapes and sizes depending on the types of food available on each island.

Adaptive Radiation

This is when a single ancestral species rapidly evolves into many different species, often because they move into new and diverse environments with many unoccupied ecological niches. For example, the cichlid fish of Lake Victoria in Africa evolved into hundreds of different species with different feeding habits and body shapes, allowing them to exploit different parts of the lake ecosystem.

Hardy-Weinberg Principle

This is a mathematical model that describes how genetic variation is maintained in a population over time, assuming certain conditions are met (such as no mutation, no migration, random mating, no selection, and a large population size). Essentially, it predicts that the frequencies of different alleles (versions of a gene) will remain constant from generation to generation if these conditions are met. For example, if a population of snails has two alleles for shell color (brown and green) and the frequency of the brown allele is 0.6, then the frequency of the green allele should be 0.4 if the population is in Hardy-Weinberg equilibrium. 


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Biological Evolution FAQs

What is the proof for evolution?

The fossil record, comparative anatomy, comparative embryology, and molecular biology are all sources of evidence for evolution.

What is the process of natural selection?

Natural selection favours individuals with characteristics that are best suited to their environment. Individuals with these traits are more likely to survive and reproduce, so they become more common in a population over time.

What exactly is the distinction between evolution and adaptation?

Evolution is the process by which living organisms’ species change over time, whereas adaptation is the process by which a species becomes more suited to its environment through the accumulation of changes in its traits over time.

What exactly is genetic drift?

Genetic drift is an evolutionary mechanism characterized by random changes in the frequency of a population’s alleles over time. It is not founded on the principle that certain characteristics provide a survival advantage, as natural selection is.

Can evolution happen quickly?

Yes, in certain conditions, including such rapid changes in the environment or the introduction of a fresh selective pressure, evolution can occur quickly. In most cases, however, evolution occurs progressively over many generations.

What role does genetic mutation play in evolution?

Genetic mutations are important in evolution because they provide raw material for natural selection to act on. Genetic mutations that offer a survival advantage become more common in a population over time.

Is evolution a violation of thermodynamic laws?

No, evolution does not violate thermodynamic laws. Evolution is a biological process that is fueled by mutations, selection, and genetic drift. The laws of thermodynamics are physical laws that govern how matter behaves.

Kathleen Currence is one of the founders of eTutorWorld. Previously a middle school principal in Kansas City School District, she has an MA in Education from the University of Dayton, Ohio. She is a prolific writer, and likes to explain Science topics in student-friendly language. LinkedIn Profile

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