Evolution
The unifying theory of biology. All life on Earth is related through common descent and shaped by natural selection.
🌿 Natural Selection
Proposed by Charles Darwin in 1859. Organisms with traits better suited to their environment survive and reproduce more. Over generations, beneficial traits become more common. This is the primary mechanism of evolution.
🧬 Modern Synthesis
The modern evolutionary synthesis combines Darwinian natural selection with Mendelian genetics and population genetics. Evolution is defined as a change in allele frequencies in a population over time.
🌳 Speciation
New species form when populations become reproductively isolated. Geographic separation (allopatric speciation) is most common. Over time, isolated populations diverge until they can no longer interbreed. Darwin's finches in the Galapagos are a classic example.
🦴 The Fossil Record
Fossils provide direct evidence of past life. The record shows a progression from simple to complex organisms, with major extinction events (including the K-Pg event 66 million years ago that wiped out non-avian dinosaurs) causing mass die-offs and subsequent diversification.
🤝 Common Ancestry
All life on Earth shares common ancestors. Humans and chimpanzees share 98.7% of DNA. Humans and yeast share about 31%. Homologous structures (like the forelimbs of humans, whales, and bats) reveal shared ancestry despite different functions.
⏱️ Timeline of Life
Life began around 3.8 billion years ago. Multicellular life appeared around 600 million years ago. Land plants colonized land 470 million years ago. Dinosaurs ruled from 230-66 million years ago. Modern humans (Homo sapiens) appeared around 300,000 years ago.