What is Natural Selection?

Natural selection is a core concept of evolution. To understand it, we must first look at descent with modification and common descent. Descent with modification is the observable fact that offspring differ slightly from parents and each other due to random genetic mutations. Common descent posits that all life on Earth is related, stemming from a single ancestor through gradual descent with modification over generations. This is a conclusion based on extensive evidence from fossils, genetics, anatomy, mathematics, biochemistry, and species distribution.

Historically, common descent faced rejection because it couldn't explain how complex, ordered life could arise from random chaos alone. Living organisms display extreme complexity, and descent with modification produces only random variation. The challenge was to explain how complex life evolved from simple life through random variation, a puzzle solved by Charles Darwin's discovery of natural selection.

Naturalist Charles Darwin, during his global travels, became fascinated by common descent. He observed that islands harbored unique species resembling those on nearby continents, suggesting a common origin. For example, Galapagos tortoises, while distinct from African species, were similar to a South American species. Darwin hypothesized that an ancestral tortoise might have drifted to the islands and, through descent with modification, evolved into distinct island species.

Darwin noted that island creatures weren't randomly different but remarkably adapted to their specific environments. Galapagos tortoises on islands with abundant grass had dome-like shells, while those on islands with scarce grass had expanded front legs and saddle-like shells to reach high cactus pads. This suggested a 'sculpting' process that random descent with modification alone couldn't explain.

To understand this sculpting, Darwin turned to selective breeding. Farmers have long transformed wild plants and animals into domestic forms by selectively breeding individuals with desired traits. Random variations create new traits, and farmers choose which ones to propagate. For instance, broccoli, cauliflower, kale, Brussels sprouts, and cabbages all originated from a single weed through human selection for different traits.

Darwin proposed that nature itself acts as a selector. Despite lacking intelligence, nature is a harsh environment. When organisms produce varied offspring, natural challenges determine which variations survive and reproduce. Over generations, this leads to creatures becoming increasingly fit for their specific environments. Darwin termed this process Natural Selection, which is now an observable fact and has greatly advanced our understanding of the natural world, allowing for serious consideration of common descent.

Natural selection is the process by which random evolutionary changes are consistently and orderly selected for by nature. Descent with modification generates new traits randomly, and nature then chooses which traits persist. Positive changes accumulate over generations, while negative traits are discarded. This continuous process enables nature to produce incredibly complex and beautiful life forms, even without a conscious mind.