In this task, we ask you to rewrite a sentence in simple English without changing its general meaning. Essentially, you want to make the sentence easier to read by using simpler words, utilizing more straightforward sentence structures, and omitting non-essential information etc.

The earliest clear statement of how chromosomes may spread in a population not because of their positive fitness effects on the individual organism , but because of their own " parasitic " nature came from the Swedish botanist and cytogeneticist Gunnar O ̈ stergren in 1945 .
The Swedish botanist and cytogeneticist Gunnar O ̈ stergren in 1945 noted how chromosomes may spread in a population because of their own ” parasitic ” nature .