Biology Quote by Carl Sagan
““In less than ten thousand years, domestication has increased the weight of wool grown by sheep from less than one kilogram of rough hairs to ten or twenty kilograms of uniform, fine down; or the volume of milk given by cattle during a lactation period from a few hundred to a million cubic centimeters. If artificial selection can make such major changes in so short a period of time, what must natural selection, working over billions of years, be capable of? The answer is all the beauty and diversity of the biological world. Evolution is a fact, not a theory.””
About This Quote
Source Book: Cosmos, Carl Sagan, 1980
Domestication shows rapid, large‑scale change; thus natural selection over billions of years can produce the immense diversity of life.
In simple terms: Artificial selection proves evolution can create big changes quickly.
Key Takeaway
Recognize evolution’s power and evidence.
Themes
evolution
domestication
science
diversity
Mood
inquisitive
reflective
Type
educational
explanatory
When to use this quote
- agricultural breeding
- conservation biology
- education
- public outreach
Key Concepts
natural selection
artificial selection
genetics
Questions to Reflect On
- How does artificial selection illustrate natural processes?
- What evidence supports evolution beyond domestication?
A Different Perspective
Complex traits may involve many genes, making direct inference difficult.
![“[ When a religious couple wrote to Sagan about fulfilled prophecies, he wrote back in May 1996 :] If ‘fulfilled prophecy’ is your criterion, why do you not believe in materialistic science, which has an unparalleled record of fulfilled prophecy? Consider, for example, eclipses.” quote by Carl Sagan](https://sms4smile.com/quotes/img-quotes/875/carl-sagan-160_belief_when-a-religious-couple-wrote-to-sagan-a_25095.jpg)
