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Our Evolutionary Inheritance

Help Lien : L'origine de la vie : Les propriétés de l'écosystème (VI) Lien : Les plus anciennes traces de vie Lien : Cosmology: The Study of the Universe
Lien: L'univers, la matière, l'évolution... Lien : L'âge de l'Univers par ses constituants Lien : Cosmos 'a billion years older' Lien : L'univers a-t-il vraiment son âge ?
Original modules
Tool Module: What Is Evolution? What Is Evolution?

All matter is composed of atoms, and atoms in turn tend to bond together to form molecules. These molecules thereby acquire new properties that the atoms alone did not possess. Such properties are called emergent properties.

For example, some molecules, such as lipids, have parts that are repelled by water, or “hydrophobic”. These molecules tend to turn their hydrophobic parts to one another, to avoid contact with water. A double layer of lipids thus forms. This layer can close on itself to create an internal environment and an external environment... in other words, a cell membrane.The cell can then begin to develop more complex structures.


According to the theory of the Big Bang, the universe as we know it was born about 14 billion years ago (12 to 16 according to the methods of calculation). Our sun and the planets formed much later: about 4.6 billion years ago. The earliest traces of living things on Earth date back 3.8 billion years. Thus, we can say that life on Earth began some time between 4.6 and 3.8 billion years ago.

The appearance of life on Earth was part of a broader process that had been going on since the Big Bang: an increase in the complexity of matter. At some point in time, the structure of the molecules of which matter was composed became so complex that they took on new properties, those of living things. At this point, chemical evolution left off and biological evolution began.

Source: University of California, San Diego
Center for Astrophysics and Space Sciences

The first living things must have resembled the bacteria present on Earth today. These early organisms had three new basic characteristics:

- a permeable membrane that separated them from the outside world;

- genetic material that enabled them to replicate (reproduce);

- proteins that constituted the actual building blocks of life, for which the assembly instructions were contained in these organisms’ genetic material.

All living cells, whether they come from a mouse or a whale, a bacterium or a banyan tree, have three things in common. All of them have a cell membrane, proteins, and a genetic code made up of DNA.

The universality of this genetic code is one of the strongest pieces of evidence for evolution and for the common relationship among all living things. Genes are long sequences of DNA that contain the instructions for making proteins. Some of these genes are present in identical form both in human beings and in far less evolved life forms, such as shellfish.

Lien: La reconstruction / déconstruction de l'arbre de vie


Lien : MEMBRANE Lien : GÈNE Lien : ADN
Chercheur : Cyrille Barrette

Shedding Some Light on the First Cell Membranes

The molecules that compose living organisms are made up of the same atoms as the molecules that compose non-living matter. Thus organic molecules differ not in the nature of their components, but rather in the way that these components are arranged.

Organic molecules do, however, show a marked tendency to contain certain atoms, such as carbon, oxygen, hydrogen and nitrogen. Organic molecules also contain smaller but still appreciable amounts of calcium, phosphorus, potassium, sulphur, sodium and magnesium.

With the possible exception of the simplest atom, hydrogen, which formed during the first few moments that the universe existed, most of the atoms found in the human body were formed through fusion of simpler atoms in the intensely hot centres of early stars. When these stars died, they exploded, ejecting vast clouds of all these atoms out into space. In this way, the evolution of the cosmos provided the elements without which life itself could never have evolved.


Human brain cells, just like the first cells that appeared on Earth, are composed of a certain number of basic ingredients whose presence seems to be an essential condition for all living things on this planet.

First of all, water accounts for about 80% of the mass of every form of life. This is because the first living cells originated in the water.

Second, the complex molecules that characterize living organisms are made up of simpler molecules that constitute the basic building blocks of life.

For example, lipids, or fatty acids, are the molecules from which cell membranes are made. Simple sugars, the cells preferred energy source, are stored in long chains of complex sugars.

Proteins, which form the structure of cells and promote certain essential chemical reactions, are composed of chains of 20 different smaller molecules called amino acids. These chains can be several hundred amino acids long. The chains forming any given protein are twisted together in a unique way that gives that protein its function.

The genetic material in each cell contains the coded instructions for all the components of that cell and is the only part of the cell that can replicate itself. The basic building blocks for this genetic material are called nucleotides. Just four nucleotides form the long chains of DNA and RNA. It is the sequence of these nucleotides on these chains that provides the genetic information needed to build all the other components of the cell.

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