lesson 1: Evolution and theories of origin of life

Video Lesson:

Competencies:

By the end of this section, the learner will be able to:

• Explain evolution and its role in genetic changes over generations.
•  Discuss different theories about the origin of life.
• Describe natural selection, mutation, meiosis, and hybridization.
• Evaluate scientific evidence supporting or refuting origin theories

Brainstorming Questions:

1. “Can you imagine where living things first appeared in this universe?”

2. “What do you think was the first form of life on Earth?

3. “How do you believe life evolved from simple organisms to complex beings?”

Key words

• Evolution: The gradual change in the genetic makeup of a population over generations, influenced by processes like natural selection, mutation, meiosis, and hybridization. This can lead to the development of new species.
• Origin of Life: Refers to the emergence of self-replicating, heritable organisms. Various theories explain this, ranging from intelligent design to scientific theories like the Big Bang and biochemical evolution.
• Special Creationism: A belief that life on Earth was created by a divine or supernatural force. This view varies across religions and contrasts with scientific explanations of evolution.
• Spontaneous Generation (Abiogenesis): The disproven theory that life can arise from non-living matter. Louis Pasteur’s experiments demonstrated that microorganisms from the air cause contamination, proving that life comes from existing life.
• Eternity of Life: A theory suggesting that life has always existed in the Universe, which is also eternal and unchanging. Proponents argue that life is a fundamental characteristic of the Universe.
• Cosmozoan Theory (Panspermia): Proposes that life came to Earth from outer space, carried by meteorites or cosmic dust in the form of spores or simple particles. These particles then evolved into various life forms on Earth.
• Biochemical Origin: A theory that life evolved from simple organic molecules formed from abiogenic materials in Earth’s early atmosphere. This idea was supported by experiments like Miller’s, which showed how organic compounds could arise from basic elements.
• Autotrophs: Organisms that produce their own food using inorganic materials. They are the foundation of food chains. The first autotrophs were likely prokaryotes, which evolved into various life forms. There are two main types: chemoautotrophs and photoautotrophs.
• Chemoautotrophs: Organisms that obtain energy from chemical reactions and use carbon dioxide as their carbon source. Found in extreme environments, they are considered one of the oldest forms of life on Earth.
• Photoautotrophs: Organisms that use light energy and inorganic carbon to produce organic materials, typically through photosynthesis. Eukaryotic photoautotrophs utilize chlorophyll in chloroplasts to capture light energy

Evolution is the change in a population’s genetic makeup over generations, driven by factors like meiosis, hybridization, natural selection, and mutation. This process can cause populations to diverge and potentially lead to the emergence of new species.

1.1. Theories of the origin of life

The origin of life refers to the development of self-reproducing, heritable organisms. Historically, this topic was debated between intelligent design and creationism. The Big Bang theory introduced ideas about how complex life evolved from simple cells through self-organization, paralleling the universe’s evolution from simple to complex structures.

what is the theories that explain about the origin of life?

There are several theories about the origin of life. Some of them are mentioned below.

• Special creationism
• Spontaneous generation (abiogenesis)
• Eternity of life
• Cosmozoan theory, Panspermia or Spore broth theory
• Biochemical origin

1.2. Special creationism

Special creationism suggests that life on Earth was formed by supernatural or divine forces, while evolution is based on scientific evidence. These two views have fundamental differences that may never be reconciled. Special creation varies among religions, each with its own interpretation of how a supreme being created life.

There are different mechanisms of special creationism theories these are:-

• Young Earth creationism
• Old Earth creationism
• Day-age and gap creationism
• Progressive creationism
• Theistic evolution/
• Evolutionary creationism
• Intelligent design

1.3. Spontaneous generation (abiogenesis)

Spontaneous generation was the belief that life could arise from non-living matter. Early thinkers like Aristotle and John Needham supported this idea, but Lazzaro Spallanzani’s experiments suggested that air carried germs, not life itself. Louis Pasteur ultimately disproved spontaneous generation with his swan-neck flask experiments, showing that microorganisms in the air cause contamination, proving that life comes only from existing life.

Louis Pasteur, the notable French scientist, showed that broth (or wine) only went sour if micro-organisms were allowed to enter. Also no micro-organisms appeared in the broth unless they were allowed to enter from the outside (Figure 1). Pasteur made a series of flasks with long, twisted necks (“swan-neck” flasks), in which he boiled broth to sterilize it (Figure 1. His design allowed air inside the flasks to be exchanged with air from the outside, but prevented the introduction of any airborne microorganisms, which would get caught in the twists and bends of the flasks’ necks. If a life force besides the airborne microorganisms were responsible for microbial growth within the sterilized flasks, it would have access to the broth, whereas the microorganisms would not.

He correctly predicted that sterilized broth in his swan-neck flasks would remain sterile as long as the swan necks remained intact. However, should the necks be broken, microorganisms would be introduced, contaminating the flasks and allowing microbial growth within the broth. Pasteur’s set of experiments irrefutably disproved the theory of spontaneous generation and also articulated “Omne vivum ex vivo” (“Life only comes from life”) F. Redi and L.paseure disproof spontaneous theory

1.4. Eternity of life

The idea that life on Earth has no beginning or end suggests that life neither requires a special act of creation nor arises from non-living matter. Advocates of this theory argue that life is a fundamental characteristic of the Universe, which has always existed alongside the Universe itself. When these ideas were popular, many prominent scientists, including Albert Einstein, believed in a static Universe. They reasoned that if life exists in an unchanging Universe today, it must have always been present.

Cosmozoan theory, Panspermia or Spore broth theory

The Cosmozoan theory suggests that life came to Earth from outer space, carried by meteorites or other cosmic materials in the form of tough spores. Proposed by Richter in 1865, the theory claims that “protoplasm”—the basic building blocks of life—arrived on Earth as tiny spores or particles from an unknown part of the universe, eventually evolving into the different forms of life we see today. Helmholz (1884) speculated that ‘protoplasm’ in some form reached the earth with falling meteorites as figure below.

1.5. Biochemical origin

The current ideas we have about how life may have evolved on Earth as a result of biochemical reactions (sometimes called abiogenesis) owe much to two biologists working early in the twentieth century.

Aleksandr Oparin, a Russian biologist who first put forward his ideas in 1924, and John Haldane, an English biologist independently put forward almost identical ideas in 1929 (before Oparin’s book had been translated into English). Both believed that organic molecules could be formed from abiogenic materials in the presence of an external energy source  such  as  ultraviolet radiation and that the primitive atmosphere was reducing (having very low amounts of free oxygen) and     contained ammonia and water vapour, among other gases. Both also suspected that the first life- forms appeared in the  warm, primitive ocean and were heterotrophic (obtaining  preformed  nutrients  from the compounds in existence on early Earth) rather than autotrophy.

They proposed that common gases in the early Earth atmosphere combined to form simple organic chemicals, and these intern combined to form more complex molecules. Then, the complex molecules became separated from the surrounding medium, and acquired some of the characters of living organisms. They became able to absorb nutrients, to grow, to divide (reproduce), and so on.

Later Miller had apparently approved the Oparin-Haldane model by mixing the basic elements to produce simple organic compounds, and then combining these to produce the building blocks of proteins and nucleic acid using spark discharging experiment that show in figure 2 .

1.6. Autotrophs

Autotrophs form the basis for all food chains: they are the organisms which create sugars, proteins, lipids, and other materials for life. The first organisms appeared about 4 billion years ago were prokaryotes. They had no true nucleus. It seems likely also that they had RNA rather than DNA as their genetic material. It was assumed that they gave rise to three distinct lines of evolution leading to:-

• Archaebacteria
• Eubacteria
• Eukaryotes

Archaebacteria:- prokaryotes including thermophilic sulphobacteria, methanobacteria and halophilic bacteria

Eubacteria:- prokaryotes; ordinary bacteria & cyanobacteria (blue-green bacteria and sometimes known as blue-green algae).

Eukaryotes:- eventually evolving into protoctistans, fungi, plants, animals (nearly all are aerobic).

One great change that affected the evolution of early life forms was the shift from the reducing atmosphere to an atmosphere containing oxygen. This took place about 2.4 billion years ago. The two major types of autotrophs are :-

• Chemoautotrophs
• Photoautotroph.

Chemoautotrophs are organisms that get their energy from chemical reactions and use carbon dioxide as their source of carbon. The most well-known chemoautotrophs are chemolithoautotrophs, which use inorganic materials like iron, hydrogen, hydrogen sulfide, sulfur, or ammonia for energy, while using CO2 for carbon. All chemoautotrophs are prokaryotes, meaning they belong to either the Archaea or Bacteria domains. They are often found in extreme environments, such as deep-sea vents, deep underground, or in acidic areas. This way of getting energy is thought to be one of the oldest on Earth.

Photoautotrophs are organisms that use light energy and inorganic carbon to produce organic materials. Eukaryotic photoautotrophs absorb energy through the chlorophyll molecules in their chloroplasts.