Question

25. The most convincing theory for the origin of eukaryotes is the serial endosymbiotic theory. Describe the major evidence supporting this theory. Once the eukaryotes evolved about 1.5 BYA, the stage was set for what new adaptations or what Dawkins called “watershed events”?

Answer 1

Mitochondria and chloroplasts are the two organelles that provide the most convincing evidences, supporting the endosymbiotic theory for the origin of eukaryotes. The major evidences are- i) mitochondria and prokaryotes both have their own cell membranes, ii) mitochondria has its own circular genome, just like the prokaryotes, and it is passed seperately to the offsprings, iii) mitochondria uses the same multiplication procedure as the bacteria, iv) mitochondria is resistant to some antibiotics, same as the bacteria.

Once the eukaryotes evolved about 1.5 BYA, certain watershed events came out, which refers to the new inventions in basic embryological plans. These were not of great survival values, but these events led to the evolutionary radiations. For example-invention of segmentation in earthworms or insects, which ultimately led to better evolution of the lineages.