Lamarckism – Theory and Example

Natural Selection and Adaptations 

 Key Concepts

• Evolution
• Emergence of evolutionary thoughts
• Lamarckism
• Acquired characters
• Lamarck’s giraffe
• Limitations of Lamarckism

Introduction

We have learnt about the history of life on Earth. The geological time scale helps to divide the history of life on Earth into different eons and eras. Different life forms were dominant during different periods. Mass extinctions caused certain life forms like dinosaurs to become extinct. The geological time scale helps to arrange all the life forms in a manner so that the older ones are at the bottom and the newer life forms are at the top of the table. Fossils are the remains of the dead and sometimes extinct organisms. They help us study about the organisms that existed in the past. 

Explanation

Evolution is the theory that suggests that all types of living things that exist today have been developed from life forms that existed earlier. Imagine you come across a horse about the size of a cat.  

Would you believe that you are looking at an ancestor of the modern horse? 

50 million years ago, Eohippus, an ancestor of the modern-day horse, was only 20 cm tall and had five toes. A modern horse is about 150 cm tall at the shoulders and has only one toe. This helps the theory that the newer species have descended from older species through a process called evolution.  

Evolution is a biological theory which states that all organisms on Earth– plants and animals have a common origin, and the differences that we can see today are the result of changes that occurred in successive generations. 

This means that all organisms that we see today on Earth have evolved from a common ancestor. 

The geological time scale tells us that Earth is about 4.6 billion years old, and the first life form emerged in the form of tiny, single-celled prokaryotes over 3 billion years ago.  

After about 2 billion years ago, those cells evolved into larger cells with a nucleus. The smaller prokaryotic cells were engulfed by the larger cells and eventually evolved into organelles like mitochondria.  

About a billion years ago, the multicellular organisms appeared. Larger animals and plants have been evolving for the past 500 million years. 

The emergence of evolutionary thoughts: 

Earlier, it was believed that the earth and all its living organisms were created by god. This theory was preached in many religions with minor changes. As years passed on, various philosophers came forward with their explanations for evolution. Biologists started to put forward their ideas of evolution. 

Today, we know that evolution is a scientific theory that explains how life changes through time. This theory is based on the scientific evidence gathered from data and observations. Many lines of evidence provide evidence for the theory of evolution. These include the comparative anatomy, DNA analysis, and the fossil record. 

Lamarckism: 

Jean-Baptiste Lamarck (1744 – 1829) was a French biologist. His theory states that living things pass acquired characteristics to their offspring. His theory is popularly known as “Lamarckism”. 

He proposed this theory in 1809. 

Acquired characters: 

Acquired characters are those characters that are acquired by an organism throughout its course of life.  Acquired characters are not present by birth, they are gained by experience. Such characters cannot be inherited. 

Examples of acquired traits include muscle development in athletes, skills like painting, swimming, dancing, singing, etc. 

Lamarck’s theory contains four main postulates: 

1. Use and disuse of organs: 

• Lamarck said that the organs that are used extensively would become stronger and larger, whereas organs that are not in use will become deteriorated. 

2. Organisms driven to a greater complexity: 

• He stated that as organisms became adapted to their surroundings, they became increasingly complex from the simpler forms.  

3. Inheritance of acquired characters: 

• He stated that characters acquired by an individual during its lifetime are inherited by their offspring as well.  
• To prove this, he explained with an example of a blacksmith. A blacksmith has strong arms due to the nature of their work. He proposed that the children of the blacksmith will inherit the development of strong muscles. 

4. Effect of environment and new needs 

• He stated that the environment influences all organisms.  
• Even a small change in the environment brings about changes in the organisms. 
• This leads to the rise of new needs, which in turn produces new structures and changes the habits of the organisms. 

Lamarck explained his theory with the example of the giraffe. He said that the ancestors of the giraffe looked like horses with small necks and forelimbs.  

As they lived in areas where there was no surface vegetation, they had to stretch their neck and forelimbs in order to eat leaves from tall plants. 

Eventually, these parts got elongated, and this trait was transmitted to future generations. 

In this example, we can see that the elongation of the giraffe’s neck is a result of variation caused due to environmental factors. The lack of surface vegetation acted as a driving force towards the elongation of a giraffe’s neck. 

As the giraffe’s neck was used extensively, the trait was passed on to the next generation. As a result, the giraffe’s of the successive generation had elongated necks. 

Adaptation is a change in the structure or behavior of an organism to survive in its environment. 

As a result, elongation of the giraffe’s neck is also considered an adaptation. 

Lamarck gave other examples like the webbed feet of aquatic birds, extinction of limbs in snakes, the vestigial wings of flightless birds, etc., to prove his theory. 

Limitations of Lamarck’s theory: 

• Lamarckism has no experimental proof. 
• New organs are not developed in organisms by their wish or requirement. 
• It is not necessary that the acquired characters are transmitted to the new generation.  

Summary

• Evolution is the theory that suggests that all types of living things that exist today have
  been developed from life forms that existed earlier.
• This means that all organisms that we see today on Earth have evolved from a common
  ancestor.
• Earlier, it was believed that the Earth and all its living organisms were created by God.
• Various philosophers and biologists put forward their ideas of evolution in the later years. One such biologist was Jean-Baptiste Lamarck (1744 – 1829).
• His theory is popularly known as “Lamarckism” and states that living things pass acquired characteristics to their offspring.
• He proposed this theory in 1809.
• Acquired characters are those characters that are acquired by an organism throughout its course of life.
• Lamarck’s theory contains four main postulates:

1. Use and disuse of organs.
2. Organisms driven to a greater complexity.
3. Inheritance of acquired characters.
4. Effect of environment and new needs.
   

• Lamarck’s theory had certain limitations as there was no experimental proof.
• It is not necessary that the acquired characters are transmitted to the new generation.