Lamarck’s Theory
The theory is based on the following;
- Environmental pressure
- Use and Disuse
- Inheritance of phenotypically acquired characteristics
It states that when the environment demanded the need or use of a particular structure in an organism (Environmental pressure), then the structure developed in response to the demand. This led to the natural use or disuse of structures producing changes in the individual during its lifetime (Use and Disuse) e.g.
Giraffes used to have short necks, when all the grass was exhausted; they started stretching their necks in search of leaves on trees. Therefore, they developed long necks which then were inherited by their offspring.
However when a structure is not continually used, it reduces in size and becomes functionless.
The phenotypical changes or structures acquired during the life time of an individual were then transmitted to their offspring and subsequent generations. This resulted in the emergence of new forms or even new species, which acquired more advantages over their ancestral forms in exploiting a particular niche.
Examples: A long necked giraffe has an advantage over a short-necked giraffe in tall canopy vegetation with highly competitive browsers.
Lamarck’s theory regarding the role of the environment phenotypic changes is true.
For instance, a body builder’s muscles develop greatly due to regular exercise.
Shortcomings of Lamarck’s Theory
The explanation that phenotypically acquired characteristics are inherited is unacceptable. Phenotypically acquired characteristics cannot be inherited.