The Never-Ending Story of Life: A Brief Journey Through Concepts of Biology

Chapter 1. The Origin of Eukaryotic Cells and Multicellular Organisms

First signs of life on Earth were most probably in form of unicellular organisms that rapidly diverged into different types while adapting to all conceivable environments. From those, the first eukaryotic cells appeared giving rise to the origin of multicellular organisms that after an unimaginable series of changes and adaptations ended in what we know today as fungi, plants and animals. This chapter explains how this long and complex process most probably happened in the last billions of years since the origin of life.

Chapter 2. Multicellular Organisms Propagation

The essential principle of life perpetuation through uninterrupted life cycles of individual organisms is described in detail. During this process, life flows by acquiring many forms such as the gametes formed by individuals, gamete fusion (egg fertilization), embryogenesis, growth and development, adulthood, sexual maturation and again, another cycle of life is initiated. Nevertheless, the key factor for this process to operate is based in the basic principle that individuals have a finite life span while life is propagated indefinitely.

Chapter 3. Grow Fast and Well or Die

Right after fertilization, most organism's early growth and development in general needs to happen very quickly. Why? Because most organisms are autonomous life forms from the very beginning of their existence. In this chapter the main strategies for multicellular organisms to produce enough offspring that would contribute to the next generation and therefore to become fertile and procreate will be described. Most remarkable, despite of the evident diversity that exists among animal species (insects, mollusks, crustaceans, birds, reptile and mammals) the fundamental principles that apply during the reproductive process are very similar.

Chapter 4. Why Do Animals Grow, Age and then Die?

As simple as it sounds, the main purpose of the multicellular organism-that is, the body of an animal-is to ensure that life will continue by ensuring transfer into the next generation. Nonetheless, from the biological point of view, life is long enough for most organisms to have a chance to grow, mature, learn, have experiences, and mate with the right reproductive partner. If this last thing occurs, the organisms can produce descendants to enhance chances of perpetuation. Once this is finish, each organism has accomplished their main purpose and therefore their remaining time will depend on how fast age, become dysfunctional and die.

Chapter 5. How Do Tissues Regenerate After an Injury?

Tissues and organs naturally regenerate through the processes called tissue and organ homeostatic regeneration or physiological regeneration. We also know that different tissues undergo homeostatic regeneration at different speeds, and can be classified as having faster, medium, or slower regeneration rates. Now, the question is what happens to tissues' capacity for regeneration after tissue injury (trauma). This type of post-traumatic regeneration is called pathological regeneration and it will depend of each tissue of how it regenerates or not by forming a scar tissue.

Chapter 6. Epilogue: The Future of Humankind Could Depend on Unicellular Life

It is very clear for most of us that life in our planet is becoming more and more restricted in terms of having enough resources to support everyone subsistence. This without question could cause in the near future a massive crisis for survival. But before this would happen we could have one or two more chances to survive. Our first option is to solve our population growth dynamics and the second is to prepare ourselves for a long trip to other words, outside our solar system. Both scenarios are considered to evaluate ho