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Evolution and the Origin of Life

One of the most misunderstood concepts of science, and most controversial (in culture), is the theory of evolution.

13.8 billion years ago, the universe was created. It contains stars, some of which have planets. On one of these planets, Earth, life began. Life has evolved over billions of years to become the diverse and complex life we see today. Evolution, the most widely accepted theory for the origin of life, explains how life has changed over time.

Definitions​

Evolution should not be understood as a deliberate or intentional process. Organisms do not volitionally choose to evolve, nor do they consciously direct the course of their own evolutionary trajectory. A giraffe does not decide for their offspring to have longer necks

Cite: Dobzhansky🔗
.

It is important to distinguish between evolution and natural selection. Evolution broadly refers to the gradual change in heritable characteristics within a population over time. Natural selection, on the other hand, is a key mechanism driving evolution. It describes the differential survival and reproductive success of individuals possessing traits that make them better suited to their environment.

Furthermore, it is essential to recognize that evolution is not synonymous with progress. It is not a linear process culminating in the production of more complex or "advanced" organisms. Rather, it is a dynamic, non-directional process, with no inherent goal or endpoint. The evolutionary process is contingent upon the interplay between genetic variation, environmental pressures, and reproductive success.

An important concept in evolution is that of a species. A species is a group of organisms that can interbreed and produce fertile offspring. Humans are, for instance, homo sapiens. Over time, species can change. This is called speciation. Speciation is the process by which new species are formed. It occurs when a group of individuals becomes isolated from the rest of the population. Over time, the isolated group may evolve into a new species. This will be discussed in more detail later.

Darwin and Natural Selection​

In the 1850s, Charles Darwin proposed the theory of natural selection. He suggested that species undergo "descent with modificaiton", and that all species share a common ancestor. He explained this through the idea of natural selection, in which a heritable trait increases its frequency in a population if it's beneficial for survival and reproduction.

Variation​

Natural selection is rooted in genetic variation among individuals within a species. This variation stems from mutations—alterations within the DNA sequence—which may arise due to environmental factors (e.g., radiation, chemical exposure) or inherent errors during DNA replication. While most mutations exert deleterious effects, a select few confer phenotypic advantages

Cite: Clancy🔗
. These beneficial mutations increase the likelihood of survival and reproduction, ensuring their propagation across generations. Conversely, detrimental mutations often compromise fitness, hindering their transmission within the gene pool.

A common example illustrating this is the case of the peppered moth (Biston betularia). Prior to industrialization, the light-colored morph predominated. However, industrial pollution darkened tree bark with soot deposits. This environmental shift conferred a selective advantage upon the darker moths, increasing their camouflage and decreasing predation. The lighter moths were subject to heightened predation, resulting in their declining numbers. Ultimately, this selective pressure led to a population shift where the majority of peppered moths exhibited the darker coloration

Cite: Rutowski and Hannam🔗
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Fine-Tuning of Earth​

The Earth exhibits numerous characteristics seemingly conducive to life: optimal solar distance, a protective atmosphere, and substantial liquid water reserves. Moreover, its magnetic field and ozone layer mitigate the effects of harmful radiation. These attributes are frequently cited within religious contexts as evidence of intelligent design

Cite: Wallace🔗
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Proponents of this viewpoint state that Earth was uniquely tailored for our particular form of life. Conversely, evolutionary theory suggests that life adapts to its environment. Natural selection favors organisms best suited to prevailing conditions, implying the potential for life to flourish on planets deviating significantly from Earth's parameters. Extremophiles, organisms thriving in seemingly uninhabitable environments on Earth (e.g., thermophiles in near-boiling geothermal springs)

Cite: National Park Service🔗
, showcase this adaptability, as well as the potential for life to exist in diverse environments.

Consequently, rather than the Earth being fine-tuned for life, it is life that has become fine-tuned to the Earth. This concept parallels the Anthropic Principle, which posits that the observable universe is contingent upon our existence within it. Alterations to the universe's fundamental constants would yield different observers perceiving a correspondingly altered reality.

Importantly, terrestrial life has reciprocally shaped the Earth. The initial atmosphere, predominantly composed of carbon dioxide, was transformed by living organisms into its current nitrogen and oxygen-rich state. Oxygen in the atmosphere is almost entirely attributable to photosynthesis:

While initial life forms were exclusively anaerobic, the oxygenation of the atmosphere proved toxic, selectively driving the evolution of aerobic organisms - including ourselves, for whom oxygen is now an existential necessity.

The universe is not really fine-tuned to life.

The vast majority of the universe is inimical to life as we understand it, with only a small fraction potentially habitable. Earth stands as the only place with life. Considering this, assertions of the universe being "meticulously designed for life" appear dubious. If such fine-tuning truly existed, wouldn't life be far more common throughout the cosmos? It's clear that the observable universe exhibits a profound indifference towards life.

Cross-species Evolution​

Life on Earth has evolved from a common ancestor. This is known as cross-species evolution. It is the most widely accepted theory for the origin of life. It is supported by a large amount of evidence, such as the fossil record, DNA, and the similarity of species.

However, some believe that evolving between species is impossible. They argue that there are no transitional fossils, and that the odds of evolving from one species to another are too low. They argue that there are no examples of one species evolving into another species.

The process, called speciation, is in fact well documented.

The future​

The inherent nature of evolution is gradual, making discernible changes within a single lifespan highly improbable

Cite: S. Baird🔗
. Nonetheless, the cumulative effect over vast periods, spanning millions of years, results in profound organismal transformations. A retrospective examination two million years in the past reveals ancestral hominids possessing markedly smaller brain capacities
Cite: Blaxland and Dorey🔗
. To extrapolate potential evolutionary trajectories, an analysis of traits directly influencing survivability and reproductive success is crucial.

Our own large brains present a compelling argument for their evolutionary advantage, at least within the last two million years. It is important to acknowledge, however, that historical trends do not guarantee the perpetual advantage of this trait. Extrapolation from the past into the future must be undertaken with caution.

References​