How eukaryotic cells arose

Examples of eukaryotes

The discovery that there are two main types of living cells (prokaryotes and eukaryotes) gave rise to a revolution in the way of classifying living things. Although (as usual) biologists do not agree on a single classification, the following one seems very reasonable:

1.      Empire prokaryote (bacteria). DNA free in the protoplasm.

a.       Kingdom eubacteria (true bacteria). They use acyl ester lipids.

b.      Kingdom archaea. They use isoprenoidal-ether lipids. They include sulphobacteria, methanobacteria and halobacteria.

2.      Empire eukaryote (cells with nuclei). DNA inside the nucleus. They have a cytoskeleton.

c.       Kingdom archaezoa (primitive eukaryotes). They have no organelles.

d.      Kingdom protozoa (advanced unicellular eukaryotes) with symbiotic organelles.

e.       Kingdom Fungi.

f.       Kingdom metaphyta (plants).

g.      Kingdom of metazoa (animals).

Outstanding problems in the history of life

Gregor Mendel

In a previous article I wrote about the origin of life and related problems. That is only the first of the outstanding issues regarding evolution. There are many more, for we are far from having an explanation for everything that happened during the history of life.

The theory of evolution through natural selection was first proposed by Darwin and refined by his followers when new discovered biological phenomena solved some of the problems posed since the beginning of the theory:

1.      The laws of heredity (Mendel, 1865).

2.      Mutations (Hugo de Vries, 1900).

3.      The laws of genetics (Thomas Hunt Morgan, early twentieth century).

4.      The synthetic theory of evolution (Simpson, Dobzhansky and others, around 1930)

5.      The transmission of inheritance through DNA (Oswald Avery, 1944).

6.      The structure of DNA and the deciphering of the genetic code (Watson, Crick, Rosalind Franklin and others).

7.      The neutral theory of evolution (Motoo Kimura, 1968).

8.      Punctuated equilibrium (Stephen Jay Gould, 1972).

9.      Epigenetics (early twenty first century).

Rosalind Franklin