Darwin, Wallace & Lamarck

This lesson covers:

  1. Early theories of evolution, such as Lamarck's
  2. The work of Darwin and Wallace in the development of the theory of evolution by natural selection
  3. Darwin and Wallace's theory of evolution by natural selection
  4. Why Darwin and Wallace's theory was only gradually accepted

Darwin, Wallace and Lamarck


Scientists' understanding of evolution has changed over time, from early theories like Lamarck's to the currently accepted theory of natural selection proposed by Darwin and Wallace.

Lamarck's theory


Jean-Baptiste Lamarck's early theory of evolution suggested that organisms could acquire new traits during their lifetime, and that these traits could be passed to their offspring.


Illustration showing a giraffe's neck growing longer over its lifetime as it reaches for leaves.

According to Lamarck's theory, giraffes have long necks because:

  1. Giraffes started with short necks adapted to lower vegetation.
  2. They stretched their necks to reach higher branches for food, resulting in longer necks during an individual's lifetime.
  3. This acquired longer neck trait was passed to offspring, and successive generations have longer necks for reaching higher branches.

Lamarck's theory was proven incorrect by modern genetics


We now know that characteristics acquired by an organism during its lifetime do not affect the DNA sequence of the organism, and cannot be passed down from one generation to the next. 

Charles Darwin and Russel Wallace


Charles Darwin made a number of important observations:

  1. Individual organisms within a species show a wide range of variation for a specific trait.
  2. Darwin observed variations between species adapted to different environments.
  3. Older layers of rock contained fossils of less complex organisms, while more recent layers showed more complex organisms.

Charles Darwin and Russel Wallace independently proposed the theory of natural selection:

In his book, "On the Origin of Species", Darwin proposed that natural selection is the driving force behind the gradual development of species over time.


Russel Wallace independently arrived at a similar conclusion to Darwin, and they later presented a joint paper together, providing additional support to the theory.

Darwin and Wallace's theory is very different from Lamarck's theory


Illustration showing two giraffes, one with a shorter neck labelled less likely to survive and one with a longer neck labelled more likely to survive.

According to Darwin and Wallace's theory, giraffes have long necks because:

  1. Some giraffes had longer necks than others, due to variation within the species.
  2. Giraffes with longer necks were better adapted to their environment, as they could eat leaves from taller trees.
  3. Giraffes with longer necks had a higher chance of surviving and reproducing, and passed on the trait of long necks to their offspring.
  4. Over many generations, this process produced modern giraffes, with very long necks.

It took time for the theory of evolution to become widely accepted


Many people didn't accept Darwin and Wallace's theory, for several reasons:

  1. Religious reasons - Darwin's theory challenged the religious belief that God created all life forms.
  2. Lack of evidence - a lack of hard evidence made many scientists hesitant to accept Darwin & Wallace's theory.
  3. DNA hadn't been discovered yet - the mechanism for inheritance and variation, now understood through genetics, was unknown during Darwin's time.

According to Darwin and Wallace's theory, what is the driving force behind the gradual development of species over time?

Environmental adaptation

Genetic mutation

Inheritance of acquired traits

Natural selection

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According to Darwin and Wallace's theory, why do giraffes have long necks?

All of the above

Giraffes with shorter necks had a higher chance of surviving and reproducing

Giraffes with longer necks were better adapted to their environment

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According to Lamarck's theory, giraffes have long necks because:

None of the above.

Giraffes started with short necks adapted to lower vegetation.

They stretched their necks to reach higher branches for food, resulting in longer necks during an individual's lifetime.

This acquired longer neck trait was passed to offspring, and successive generations have longer necks for reaching higher branches.

Giraffes have always had long necks.

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According to Lamarck's theory, why do giraffes have long necks?

Giraffes stretched their necks to reach higher branches for food.

Giraffes have always had long necks.

Giraffes started with long necks adapted to lower vegetation.

Giraffes acquired longer necks during their lifetime and passed this trait to their offspring.

Giraffes inherited long necks from their ancestors.

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