History of Life on Earth

Natural Selection

Step 1: Charles Darwin proposed Natural Selection as the primary mechanism driving evolution. Step 2: Natural selection means 'survival of the fittest' - organisms with advantageous traits survive and reproduce more. Step 3: Those with less favorable traits are eliminated over time through the 'struggle for existence'. Step 4: This process leads to gradual changes in populations over generations. Step 5: Darwin observed this during his voyage on HMS Beagle, particularly studying finches on the Galapagos Islands.

Darwin's theory modified with Mendelian genetics

Step 1: Darwin didn't know how heritable variations arose or were passed to offspring. Step 2: Mendel's principles of genetics were discovered around the same time but Darwin wasn't aware of them. Step 3: Later scientists incorporated Mendelian genetics into Darwin's theory. Step 4: This combination became known as Neo-Darwinism or the Modern Synthetic Theory of Evolution. Step 5: It explains both how variations occur (through genes/mutations) and how they're inherited (through Mendel's laws).

1.5-2 million years ago

Step 1: Fossil evidence shows human evolution began approximately 1.5-2 million years ago. Step 2: This coincided with climate changes and glaciation that reduced forest cover. Step 3: Human ancestors had to adapt from tree-dwelling to ground-walking lifestyle. Step 4: The first human-like ancestor was Australopithecus, including the famous fossil 'Lucy'. Step 5: Modern humans (Homo sapiens sapiens) evolved only about 50,000 years ago.

Homo sapiens sapiens

Step 1: Modern humans are scientifically classified as Homo sapiens sapiens. Step 2: 'Homo' refers to the genus (human), 'sapiens' means wise. Step 3: The double 'sapiens' distinguishes modern humans from earlier Homo sapiens like Neanderthals. Step 4: This classification reflects our advanced cognitive abilities and cultural development. Step 5: Modern humans evolved about 50,000 years ago and have remained largely unchanged biologically since then.