Giant Viruses

John Maynard Smith

In 1966, H.J. Muller defined living beings as follows: Any being capable of multiplying with inheritance and variation. With this definition, which prioritizes reproduction and evolution as the definition of life, viruses should be considered as living beings. Other biologists, such as John Maynard Smith, thought that this criterion was too broad. It would mean that nucleic acids are alive, since they are capable of reproducing with inheritance and variation. That is why they propose adding another criterion: A living being is capable of reproducing and metabolizing. This would exclude nucleic acids, and therefore viruses, which are nucleic acids enclosed in a protein capsule, and viroids, which are isolated nucleic acids.

The tree of life, the family tree of all species of living beings, seems to indicate that all beings formed by one or more cells descend from a single individual, the first living being, which is called LUCA (Last Universal Common Ancestor). As I said in another post, some think that perhaps LUCA was not a single individual, but a network of individuals. But where do viruses come from?

Biological evolution and cultural evolution in the history of life and man

The title of this post is the translation into English of a book of mine, published in 2017 by the publisher CEU Ediciones. As its name implies, the book is divided into three main parts, the first of which (the first four chapters) reviews the origin, evolution and history of life (biological evolution), while the second (chapters 5 and 6) focuses on the origin, evolution and history of man (cultural evolution). Finally, the third part (chapters 7 to 9) compares both types of evolution, emphasizing their similarities and differences; reviews the current situation of human evolution; and offers some ideas about the future.

As is often the case, this book did not come out of nowhere, but rather builds on previous works of mine. Especially in the first part, some of the titles of some chapters and subchapters may be familiar to the readers of my blog, because they are similar to some of my posts:

Science and civilizations

In my book Biological Evolution and Cultural Evolution in the History of Life and Man, published in Spanish, I analyze the cultural history of 23 civilizations and compare their evolution. In the particular case of science, I wrote this:

...the first-generation civilizations (Mesopotamia, Egypt and the American) reached their maximum scientific development in mathematics and astronomy. Egypt and Mesoamerica added medicine to these sciences. A second-generation (Greco-Roman) and a third-generation civilization (Islam) also practiced the natural sciences. As for the West, it is a unique and unprecedented case, as its scientific development has been overwhelming.

...astronomy was the first cultivated science... Mathematics emerged in parallel... It was soon found that both sciences were related, for mathematics supported astronomy, making it possible to perform complex calculations and predictions.

The pagan religions... tried to predict the future, using for that purpose sacrificed animals, which led to an accumulation of anatomical knowledge, soon applied to man, which mixed with ancient knowledge about the properties of medicinal plants, led to the formation of a corpus of medical doctrines.

On the other hand, the development of the physical, chemical and biological sciences was less urgent... and so it was attempted only by civilizations that had freed from the necessities of survival an important part of human work... This happened for the first time in Greece, the cradle of philosophy and most of the modern sciences.

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