Evolution and Adaptation

Grade 7 · Science · Study Guide

An introduction to how species change over time through natural selection and how adaptations help organisms survive in their environments.

Evolution is the process by which populations of organisms change over many generations. Charles Darwin proposed the mechanism of natural selection, which explains how evolution happens. The idea is straightforward: individuals in a population naturally vary. Some variations are heritable — they can be passed from parent to offspring. If a variation helps an individual survive and reproduce in its environment, that individual will tend to have more offspring, passing that trait on. Over time, helpful traits become more common in the population.

An adaptation is any inherited trait that increases an organism's chances of survival and reproduction in a specific environment. Adaptations can be structural (like a bird's beak shape), behavioral (like migration), or physiological (like the ability to store water in a cactus).

Evidence for evolution comes from many sources: the fossil record shows gradual changes in species over millions of years; comparative anatomy reveals similar bone structures in very different animals (like the forelimb bones of humans, whales, and bats); and DNA comparisons show how closely related different species are.

Speciation — the formation of new species — occurs when populations become isolated and evolve differently over time. Natural selection does not mean organisms choose to change or that change is always toward 'better' — it simply means that traits which improve survival in a given environment become more common over time.

Key terms

Evolution
The change in the heritable characteristics of a population over successive generations.
Natural selection
The process by which organisms with favorable traits survive and reproduce more successfully, passing those traits to offspring.
Adaptation
An inherited trait that improves an organism's ability to survive and reproduce in its environment.
Fossil record
The collection of all known fossils; provides evidence of how organisms have changed over time.
Variation
Differences in traits among individuals in a population that can be inherited.
Speciation
The evolutionary process by which new, distinct species form, often when populations become geographically isolated.

Flashcards

Natural selection
The process where organisms with traits better suited to their environment survive and reproduce more, passing those traits to offspring.
Heritable trait
A characteristic that can be passed from parent to offspring through genes.
Survival of the fittest
A phrase summarizing natural selection — organisms best suited to their environment are most likely to survive and pass on their traits.
Structural adaptation
A physical feature of an organism (like a duck's webbed feet) that helps it survive in its environment.
Behavioral adaptation
A behavior (like hibernation or migration) that helps an organism survive in its environment.
Common ancestor
A shared ancestral species from which two or more different species descended over time.
Fossil
The preserved remains, traces, or impressions of an organism that lived in the past.
Camouflage
An adaptation where an organism's coloring or shape blends in with its surroundings, helping it avoid predators.

Questions

  1. Which scientist proposed the theory of natural selection as the mechanism for evolution?

    1. Gregor Mendel
    2. Louis Pasteur
    3. Charles Darwin
    4. Albert Einstein
    Show answer

    Answer: Charles Darwin

    Charles Darwin published his theory of natural selection in 'On the Origin of Species' in 1859 after observing variation among animals during his voyage on the HMS Beagle.

  2. An adaptation is a trait acquired during an organism's lifetime that helps it survive, even if it cannot be passed to offspring.

    Show answer

    Answer: False

    An adaptation must be heritable — able to be passed from parent to offspring through genes. A trait gained during a lifetime (like muscles from exercise) is not an adaptation in the evolutionary sense.

  3. The preserved remains or traces of ancient organisms are called ______.

    Show answer

    Answer: fossils

    Fossils are the preserved remains, casts, or traces of organisms from the past. They are found in sedimentary rock and provide direct physical evidence of evolution over time.

  4. A population of moths lives in a forest. Dark-colored moths survive better on dark tree bark because they are harder for birds to spot. After many generations, what would you expect?

    1. The population would have more light-colored moths
    2. The population would have more dark-colored moths
    3. The population would remain unchanged
    4. All moths would become the same shade
    Show answer

    Answer: The population would have more dark-colored moths

    This is natural selection in action. Dark moths survive better (are harder for birds to spot on dark bark), so they reproduce more. Over generations, the dark-moth trait becomes more common — this is evolution.

  5. DNA evidence can be used to determine how closely related two species are.

    Show answer

    Answer: True

    Scientists compare DNA sequences between species. The more similar the DNA, the more closely related the species are — and the more recently they shared a common ancestor.

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