Evolution: Key Concepts and Historical Context

Scientific process begins with observations; a hypothesis is a possible explanation based on observations.

Descent with modification: all living organisms descended from pre-existing organisms; traits are inherited and some traits become modified over time.
Example: whales and dolphins descended from land mammals; their bodies became adapted to life in water.

Darwin lived in the $1800s$ ; his hypotheses were revolutionary and radical at the time.
Before Darwin, many in the Western world believed in a fixed, unchanging set of living organisms and a very young Earth.
Traditional view: Earth was about $6{,}000\text{ years}$ old; species were fixed and Horse-type organisms were thought to be the original forms.
The Darwinian revolution challenged the view of a young Earth and fixed species.

We will discuss the people on the timeline and how their work influenced Darwin, without requiring memorization of every date.

Aristotle lived around $384\text{ BC} \text{ to } 322\text{ BC}$ and sought to explain biological diversity.
He and others believed species were fixed (unchanging over time).
Scala Naturae (ladder of nature): a hierarchical ranking of life.
- Bottom: inanimate matter (e.g., rocks, soil).
- Next: lower plants (e.g., moss; fungi often considered plants at the time).
- Above: higher plants (trees, flowering plants).
- Above: simple animals.
- Top: humans.

Carl Linnaeus lived in the $1700s$ and developed the system of binomial nomenclature.
Each described species has a scientific name consisting of two parts: genus name and species name.
Examples:
- Humans: $\text{Homo sapiens}$ where $\text{Homo}$ is the genus and $\text{sapiens}$ is the species.
- Domestic dog: $\text{Canis familiaris}$ where $\text{Canis}$ is the genus and $\text{familiaris}$ is the species.
Within each genus there can be many species.