Jean-Baptiste Lamarck's Theory of Evolution: Overview

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  • 0:00 How Are Traits Inherited?
  • 0:53 Larmarck's Theory of…
  • 2:29 Inheritance of…
  • 4:43 Challenges to Lamarck's Theory
  • 5:43 Judging Lamarck's Impact
  • 6:10 Lesson Summary
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Lesson Transcript
Instructor: Angela Hartsock

Angela has taught college Microbiology and has a doctoral degree in Microbiology.

You might know about Charles Darwin and his theory of evolution. However, it was the lesser known, yet influential, Jean-Baptiste Lamarck who put forth a theory that laid the early foundations for the study of evolution.

How Are Traits Inherited?

Think about the following scenario: a child decides that she wants to be a bodybuilding champion and earn the Ms. Intergalactic title. She spends six hours every day for ten years in the gym and earns the coveted crown as Ms. Intergalactic! Having accomplished this goal, Ms. Intergalactic decides that since she has worked so hard, she should have children so she can pass on her strength to her children. The question is, will the children born to Ms. Intergalactic inherit her strength?

You may have already correctly assumed that, no, the children would not inherit her strength. However, if you posed that same question in the early 1800s, the theory of evolution that was prevalent at the time would have said that Ms. Intergalactic's children could, in fact, inherit her strength.

Lamarck's Theory of Inheritance

Jean-Baptiste Lamarck (1744-1829) was a French naturalist and biologist who laid the groundwork for the current theories of evolution. Scholars before Lamarck had attempted to explain evolution as a natural, organic changing of species, but what made Lamarck stand apart was that he was the first person to develop and present a plausible mechanism for this change.

Lamarck's theory can be boiled down to two broad claims. First, new species evolved from previous species. Today, we know that each organism carries DNA that encodes the characteristics or traits that we associate with its species. This DNA is inherited from parent to offspring and small changes in the DNA over millions of years result in the diversity of species that we see today.

As you can imagine, in the 1700s, DNA had not even been discovered yet, and genetics experiments were not available to Lamarck. He based this tenet on observation and his idea that all species could be ordered from simplest to most complex. By examining this order, you could trace the development of new traits and species up the complexity ladder.

Now, with our contemporary understanding of Charles Darwin's theory of evolution, we know this tenet at its most basic is correct: New species result from small, incremental changes inherited from parent to offspring. Experimental evidence has continued to support the basics of Lamarck's claim. However, the details of his theory, including the ordering of species based on complexity, are not accurate. Organisms found in the fossil record show the same complexity as organisms found today.

Inheritance of Acquired Characteristics

Lamarck's second broad claim was, acquired traits are inherited by offspring. Lamarck's second tenet is that this evolution of species occurs by the inheritance of acquired characteristics (like Ms. Intergalactic's strength). We now know that this is incorrect, but let's examine what Lamarck meant by 'acquired characteristics.'

Lamarck's theory stated that evolution worked on individuals, like Ms. Intergalactic. He postulated that any change to an individual during its lifetime would be passed directly to its offspring. So if mom has big muscles, then baby has big muscles. His classic example involved the necks of giraffes.

Lamarck observed that giraffes have disproportionately long necks. He also observed that giraffes seemed to be built perfectly for eating the leaves from the tops of trees. He hypothesized that the original giraffe had a normal sized neck but that by constantly stretching its neck up to reach leaves on higher branches, the neck would become stronger and longer. Any offspring of that giraffe would then inherit a longer and stronger neck. By each individual increasing its neck length a small amount, then passing that on to its descendants, it becomes clear how the neck was able to become so long in the modern giraffe.

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