We know that the germ cells of sexually reproducing organisms are made in specialised reproductive tissues. From the previously discussed illustration, it is clearly understood that the weight of the beetle is reduced because of starvation, and this will not cause any changes in the genetic makeup of the germ cells. Thus the condition of low weight is not a trait and hence, cannot be inherited to its progeny.
Some generations of beetles are underweight due to malnutrition; this isn't an example of evolution because the variation isn't passed down through the generations. As changes in non-reproductive tissues cannot be passed on to the germ cells, we can conclude that an individual's life experiences cannot be passed on to its descendants and cannot affect evolution.
These traits are known as acquired traits.
Thus acquired traits can be defined as follows:
The characters which are not inherited over generations via the DNA of the germ cells as they are caused due to change in the non-reproductive tissue are known as acquired traits.
The size of the beetles in the population decreased due to scarcity of food, pierced ears, scars on the manatee, children learning to read, muscular body of a wrestler, etc., are some of the examples.
Scars on the manatee, muscular body of a wrestler, pierced ears
The presence of acquired traits was proved by Weismann's germplasm theory.
In this experiment, Weismann cut off the tails of rats for \(22\) generations and allowed them to breed. However, their offsprings were again tailed because the cells responsible for the growth of the tail are somatic and are not germ cells.
An image illustrating Weismann's germplasm theory
These are caused by alterations in the DNA of germ cells from generation to generation, such as the production of green beetles in a red beetle population.
Differences between acquired and inherited traits:
|1.||These traits don't transfer to the offspring from their parent but develop in response to the environment.||These traits are developed due to the change in the gene of DNA.|
|2.||These traits develop throughout the lifetime of an individual and degenerates along with the death of the individual.||These traits are transferred through the genetic material from the parents to the offspring.|
|3.||These are formed as a result of somatic variations.||These are formed as a result of genetic variations.|
|4.||These traits are not present in the genetic makeup.||These traits are present in the genetic makeup.|
|5.||These traits cannot direct evolution.||These traits can direct evolution.|
|6.||Example: Larger muscle size, skills, etc.||Example: Hair, eye colour etc.|