1.3 Theories on the origin of organisms

The search for the fundamental units of life and their properties has generated the cell theory. Back in the XVI century Matthias Schleiden and Theodor Schwann used the new invention of the light microscope to address the important question of what defines living objects. By systematic observations and careful analysis they concluded that living objects are made of units that were called cells. This was the beginning of the cellular theory.

Let’s have a look at Figure 1.1, which shows a series of photographs taken with a phase contrast or differential interference (DIC) microscope. In the field of view you can see a single cell and over time you can notice visible changes in its structure. Based on this type of observation, cellular biologists have established the dynamic structure of single cells, a defining property of organisms.

Figure 1 Individual frames from a video of a stage-10 Germinal Vesicle of Drosophila, showing gradual formation of induced nuclear bodies. The first frame (t = 0) was taken approximately five minutes after the egg chamber had been gently squashed between a glass slide and coverslip. In this GV the first bodies to form were numerous and irregular in outline, but eventually most coalesced into three large bodies. Arrow points to the karyosome, which remained unchanged. Imaged by DIC. Bar = 10 µm. A video of another GV can be watched in the Supplemental Material. From Singer AB, Gall JG (2011) An inducible nuclear body in the Drosophila germinal vesicle. Nucleus 2:5, 403-409, DOI: 10.4161/nucl.2.5.17250

Let’s now take a different type of historical perspective and let’s consider the origins of our planet Earth. Consideration of the materials and environmental conditions of the primitive earth. The Miller experiment in the USA. The ideas of Russian scientist Oparin and the modern synthesis sparked by Margulis, Lazcano and others. The idea that water came from outer space, the evolution of the atmosphere. The idea that life arose multiple times independently on planet earth and importantly, that the first living objects were all cells.

The evolution of single cells and the existence of prokaryote and eukaryote cells. The evolution of multi-cellular organisms. The distinction between animate and inanimate life. The notion of living objects as biological systems.

Consideration of emergent properties, which are not defining properties of living systems, since they can be observed in non-living systems (Box 1.1 Magnetism as an emergent property; pendulum video).