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Natural selection

Charles Darwin developed the idea of evolution by natural selection

“Any trait that helps an organism survive and reproduce under a given set of environmental conditions is said to have adaptive value. For example, a rabbit’s ability to blend in with its surroundings may allow it to escape capture by a fox” (BRLE)

Adaptive radiation is a process in which organisms diversify rapidly into a multitude of new forms.  This may happen when a change in the environment makes new resources available, or creates new challenges.  (Wikipedia)

The below is from http://evolution.berkeley.edu/evolibrary/article/0_0_0/evo_25

Natural selection

The process is relatively simple but often misunderstood.
To see how it works, imagine a population of beetles:

  1. There is variation in traits.

    For example, some beetles are green and some are brown.

Color variation in these beetles
  1. There is differential reproduction.

    Since the environment can’t support unlimited population growth, not all individuals get to reproduce to their full potential.
    Here, green beetles tend to get eaten by birds, so they survive to reproduce less often than brown beetles do.

Differential reproduction
  1. Offspring inherit traits from parents.

    Surviving brown beetles have brown baby beetles because this trait has a genetic basis.

Heredity of the traits of the beetles who survive
  1. Some genes become more common.

    The gene for brown becomes more common in the population.
    When some genes become more common, while others become less common, we say that a population has evolved.

Eventually, the advantageous trait dominates

Download this series of graphics

If you have variation, differential reproduction, and heredity, you will have evolution by natural selection as an outcome. It is as simple as that.

Sources of variation:
1. Mutations – random mistakes in DNA when cells divide
2. Crossing over during meiosis (during production of eggs and sperm)

Results of genetic variation

Structural changes:

functional changes:

behavioral changes:


The degree of kinship between organisms or species can be estimated from the similarity of their DNA sequences; this similarity often closely matches organisms’ or species’ classification based on anatomical similarities.

The graphic above shows that:

All of these primates had a common ancestor, the ancestral primate.
The human and chimpanzee have the closest evolutionary relationship as their DNA is the most similar


Bats, dolphins, and many forms of mammals, all use adaptations of the same original five-fingered animal hand.

adaptive radiation from five fingered hand

Charles Darwin discovered adaptive radiation occurring in finches, on the Galapagos Islands.

Here is a color graphic summarizing how one species of finch radiated over time to become many.

Finches color

Here is the same information, as presented on a New York Regent’s exam.

Finches BW regents



Are all of these changes successful?

Extinction is shown on a tree of life, when a line comes to an end, without any branches.

australo hominid primate cladogram extinction

BRLE = Prentice Hall Brief Review The Living Environment (Pearson)

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