of their primitive asexual reproduction. They used simple fission, whereby
species essentially cloned themselves,which offered little evolutionary change.
A primitive form of metabolism also kept organisms in a low-energy state,
which retarded the rate of evolution.
The first major evolutionary advancement was the development of an
organized nucleus and sexual reproduction, forming a new single-celled
organism called a eukaryote (Fig. 30). It evolved from prokaryotes possibly as
early as 3 billion years ago. The eukaryotic cells were typically some 10,000
times larger in volume than prokaryotes. They contained a nucleus that sys-
tematically organized genetic material, substantially increasing the number of
mutations and the rate of evolution. Eukaryotes metabolized their energy
sources by r espiration.Therefore, their presence indicates substantial quantitiesFigure 30The
eukaryotic cell incorporates
organelles along with a
nucleus that contains the
DNA hereditary material.
Historical Geology
NucleusLysosomeGolgi bodyEndoplasmaMitochondrionVesiclesNucleus