Origin of Life and Evolution: Theories and Evidence

Theories on the Origin of Life

The primordial soup hypothesis is incapable of explaining the origin of life because the early atmosphere wasn't composed of the gases described by Oparin and Haldane. Also, we know that in the early atmosphere, there was no ozone layer, so it would make the first molecules very unstable because of UV radiation. The hypothesis was supported by the Miller-Urey experiment, which consisted of the following: a mixture of gases was put in a container, and high-voltage electric shocks were applied. Then, gases were condensed in another container, simulating the primitive ocean. Finally, several organic compounds were found in that simulated "primordial soup," including amino acids. As an alternative to the primordial soup hypothesis, the hydrothermal vents theory emerges. The first molecules could have arisen around hydrothermal vents on the ocean floor and were protected from solar radiation because they were at great depths.

Biodiversity and Evolutionary Theories

• Fixism: Independent origin, lineal (creationism, religious version).
• Transformism: Independent origin, change over time.
• Evolutionism: Species are related, all descend from a common ancestor, change.

Evidence for Evolution

1. Anatomical Evidence:

• Homologous organs: Common structure, different function (divergent evolution).
• Analogous organs: No common structure, same function (convergent evolution).
• Vestigial organs: Lose their original function in evolution (determine changes of species through evolution).

2. Paleontological Evidence (study of fossils):

• Transitional fossils: Share characteristics with present-day groups of living things.
• Living fossils: Organisms that haven't changed over time.

3. Embryological Evidence:

• Ontogeny recapitulates phylogeny: the embryos are similar if their evolutionary relationship is close.

4. Biogeographical Evidence:

• Some animal species are similar despite being found at great distances because they all descend from a common ancestral species.

5. Ethological Evidence:

• The instinctive behavior of animals has a genetic basis, so evolutionarily related species show similar behavior.

6. Molecular Evidence:

• All living things have chemical and molecular uniformity, basic metabolic processes are similar, and genetic codes are universal (evolutionary trees).

Lamarckism

Strengths:

• It recognizes the relationship between anatomical structures and their purpose.
• It explains that organisms adapt to the environment they live in.

Weaknesses:

• It claims that acquired characteristics are transmitted from parents to offspring.
• It claims that animals have an internal need to improve themselves and become more complex.

Darwinism and Modern Synthesis

Darwinism cannot explain how variations are inherited by subsequent generations. How are traits transmitted from one generation to the next? Mendel's laws and the chromosomal theory of inheritance provide an understanding of the mechanism of transmission of hereditary characteristics and their nature.

Darwinism cannot explain why individuals in a population vary slightly from one to another. What is the origin of population variability? Mutations, genetic recombination occurring during prophase I of meiosis, and randomness associated with sexual reproduction are the sources of population variability.

Adaptation

Adaptation refers to survival or reproductive success and to the characteristics of the evolutionary process in their environment.