Thursday, April 19, 2018

The end of the selfish gene

The German biologist August Weismann (1834-1914) was one of the most influential biologists of the late nineteenth century. His most important contribution was the theory of germinal plasma, also called in his honor Weismannism. According to this theory, there are two classes of cells in all multi-cellular living organisms (see Figure 1):
Figure 1
  • Somatic cells, represented in the figure by an S, that make up most of the body and do not play any role in inheritance.
  • Germ cells, represented in the figure by a G: the gametes, ovules and sperm, which pass the genetic information to the next generation.

Thursday, April 12, 2018

Epigenesis and epigenetics

Fertilization of the egg by the sperm
In the previous post we saw that at the beginning of the 19th century the theory of epigenesis seemed to have won the game. However, after 1850, and for just over a century, a cascade of new discoveries tipped again the balance towards the theory of preformation. Let us see what they were:
  1. The existence of a nucleus within animal and plant cells.
  2. The confirmation that the nuclei of the male and female gametes are fused during fertilization. This put an end to spermism and ovism and made it clear that the new being begins in the zygote.
  3. The confirmation that certain structures (the chromosomes) appear during cell reproduction inside the nucleus of the cell, which seem to play a very important role. It was also found that in the chromosomal endowment of the zygote, half of the chromosomes come from the father and the other half from the mother.
  4. A new science (Genetics) was originated in the experiments of Thomas Hunt Morgan, who showed that the chromosomes are linked to Mendelian inheritance.
  5. The works of Oswald Avery, who showed that DNA, a nucleic acid that appears in chromosomes, is the basis of Mendelian inheritance.
  6. The discovery of the structure of DNA (a double helix), made in the early 1950’s by Francis Crick, James Watson and Rosalind Franklin.
  7. The deciphering of the genetic code, which took place during the 1950s and the 1960s.

Thursday, April 5, 2018

Preformation and epigenesis

The history of the evolution of scientific theories about embryonic life (the origin of living beings) is very curious. I will try to summarize it in a couple of posts.
Throughout the history of science, the problem of the embryonic development of multicellular organisms has been one of the most arcane mysteries that man has tried to solve. Faced with this problem, two conflicting solutions have essentially been proposed:
         Preformation: During embryonic development there is just a growth of the pre-formed embryo, whose constitution and composition are completely ready-made from its origin. Everything is done from the beginning, whether in the egg, the sperm or the zygote.
         Epigenesis: Embryonic development is a process. Not everything is decided from the beginning; everything happens because something - a vital force, or an external or internal action - forces the embryo to develop in one way, rather than another.

Thursday, March 29, 2018

About the social order

In a comment to the Spanish version of a previous article in this blog, JI Gs wrote this:
All societies have an explicit social order, whether they are fundamentally believers or not in the immaterial; even animal societies, let alone insects, have a strict social order and the immaterial has no need to act to generate it or to maintain it.
I have two considerations to make:
Solitary bee (Megachile) and social bee (Apis)
  • Comparing human societies with insect societies is a false step. The human social order is based on a set of moral rules that has remained fairly constant over time, except in relation to sexual morality (see the appendix to The Abolition of Man by C.S. Lewis). The social order of insects is programmed in their genes and their nervous system. While in the human species it is possible, even frequent, that one or more members of society rebel against one or more rules, or even attempt to overthrow the entire social order, the members of insect societies cannot rebel. In other words, man is conscious and free, insects are not. Any comparison between them is out of place, because they are based on totally different structures.

Thursday, March 22, 2018

Can there be life without the weak interaction?

Beta and neutron decay

On January 30, 2018, the Science News magazine commented on an article recently published in arXiv which states that in a universe without the weak interaction, life would still be possible. When I read the Science News article, I immediately thought of an objection that could ruin both the thesis of the original article and its popularization. The first thing I did was looking up the original article, to see if my objection was mentioned or denied, but there was not a word about it. Next I detailed my objection in a comment in the web version of the Science News article, but so far no one has answered me. However, I think the objection is quite strong, and unless I am answered satisfactorily, in my opinion these articles are discredited.
According to the standard cosmological model and the standard model of particle physics, there are four fundamental interactions or forces in the universe: gravitation, electromagnetic interaction, and the strong and weak interactions, which regulate the work of atoms and elementary particles. In particular, the weak interaction affects all the elementary particles: leptons and hadrons, unlike the strong interaction, which affects only hadrons.

Thursday, March 15, 2018

Dark energy again

Albert Einstein
In a previous article I mentioned that Einstein introduced a third term in the right side of his cosmological equation, to force this equation to have as solution a stationary cosmos, that would not expand or contract. The attempt was unsuccessful, for such a cosmos would have been in unstable equilibrium, and the smallest variation would have pushed it to either expanding or contracting. The term in question depends on a constant (L, the cosmological constant), which we don’t really know what it is.
Einstein's cosmological equation
For most of the twentieth century, it was assumed that the value of the cosmological constant must be zero. In other words, the third term of the Einstein equation would not exist, wouldn’t be necessary. However, in 1998 it was discovered that the universe seems to be expanding rapidly. At least, this seems to be indicated by the study of supernovas in very distant galaxies, about one billion light-years away from us. To explain this discovery, the cosmological constant term was resurrected, but giving it a sign opposite to that proposed by Einstein, so that rather than the expansion being counteracted, it would be accelerated. This proposal has become the standard cosmological model, in which the first term of the equation, which represents the effect of the mass, currently counts as 31%, while the third, that of the cosmological constant, counts as 69%. In this model, the second is assumed to be zero. I leave apart the question that the mass term does not match, so it has been necessary to assume that there is also a dark matter, that we don’t know what it is.

Thursday, March 8, 2018

One hundred years since The Decline of the West

Oswald Spengler
This year it will mark one century since the publication in 1918 of the first volume of the book The Decline of the West, by Oswald Spengler. The second volume was published five years later, in 1923. This book was the first to raise the idea that our famed Western civilization is in decline. What can we say about it, a hundred years later?
The great historian of the twentieth century, Arnold J. Toynbee, agreed with Spengler on his fundamental idea, although not in the details. For Toynbee, Western civilization collapsed in the twentieth century, when the two world wars proved its inability to face new challenges. Of course, for Toynbee, the collapse of a civilization does not mean its disappearance, it does not even prelude it. We still have ahead - according to him - a few centuries of what Toynbee calls the Universal Empire, linked, however, to a certain cultural stagnation.
The first thing we have to notice is: if Spengler actually managed to detect the decadence of our civilization, it means that the decline had begun much earlier. Evolutionary movements, both biological and cultural, are imperceptible at the beginning. When they become visible, they are quite advanced in their development.