Inheritance of Acquired Traits



Misconception: Some people think that traits acquired during the lifetime of an organism are passed on to their offspring.They think that these passed acquired traits are what cause evolutionary change.
  • The classic example of this is that giraffes must stretch their necks in order to reach the leaves on the trees. Since they stretch their necks they get a little longer and this extra length is passed to their offspring.
  • Another example is that of a weightlifter. If someone were to lift weights and acquire large muscles they would pass on these large muscles to their child.
  • If someone goes tanning a lot and has tan skin they will pass this to their offspring.


The Correct Explanation: Evolutionary change happens primarily through natural selection. Populations of organisms have variation. Individuals are different. Certain individuals may have a difference that gives them some kind of advantage. Because of this advantage they will be more likely to reproduce and pass on whatever their advantage may be. If this happens for many generations that advantageous trait will become more prominent in the population.

For example, if giraffes were living in an area with tall trees those giraffes with the longest necks (due to natural variation in their genotypes) would be able to reach more food. They would have some advantage over those with shorter necks and would be more likely to reproduce. Over many generations the proportion of longer necks in the population would be higher than the short necks. Eventually the genes for short necks may even be lost or become rare in the gene pool. One must also consider that the trees in this story would also be subject to natural selection. The taller trees would be less likely to be eaten by giraffes. So as the trees became taller the necks of the giraffes would become longer. They would be evolving in response to each other (coevolution).

So rather than the long neck being acquired by an individual and then passed on, the proportion of long necked individuals in the population that lived to reproduce would be greater than the proportion with short necks that reproduced. This causes an increase in the occurrence of the trait in the population over time.


Cause of Misconception: This misconception has been common throughout the last few centuries. It was outlined by Jean-Baptiste Lamarck in the early 1800s. The most common reason for this misconception is that natural selection is not very obvious and does not follow from everyday experience. Inheritance of acquired traits makes sense superficially and agrees with experience. There is a deep rooted concept that animals do things because they need to. While this is true, it leads to the idea that traits are lost through disuse and enhanced through use. A giraffe's neck is longer because it needs to reach the leaves and it uses its neck to get the leaves. If a giraffe were to start eating from bushes people might think that it would have a short neck because it did not use it. Basically this is a common misconception because thinking that traits that are enhanced through use and are passed on is more intuitive than the mechanisms of natural selection, even though it is inaccurate.


Reference:
Gregory, Ryan T., Understanding Natural Selection: Essential Concepts and Common Misconceptions. Evo Edu Outreach (2009) 2:156–175