Evolutionary Trees (Cladograms)
What does a node (a fork/split point) on an evolutionary tree represent?
An ancestral species (or common ancestor) splitting into two or more descendant species
Life originated in the oceans around 4.28 billion years ago. For roughly how long did life remain exclusively in the water before moving to land?
For over 3.75 billion years (land life started ~550 mya during the Cambrian explosion).
How did 13 distinct species of finches end up on the Galápagos Islands?
They all evolved from a single ancestral finch species that arrived from the mainland 2–3 million years ago.
What type of geographical barrier separated the salamander populations as they migrated south through California's Central Valley?
The Central Valley itself (a hot, dry environment between the coastal mountains and Sierra Nevada ranges).
Out of all the species that have ever evolved on Earth over the last 4 billion years, approximately what percentage are now extinct?
Over 99%
According to the vertebrate evolutionary tree, which group split off most recently from birds: mammals or crocodiles?
Crocodiles (~150 mya split)
What was the "Cambrian Explosion"?
An event around 550 mya where a wide variety of major animal groups evolved in a relatively short period (~20 million years).
What physical trait changed significantly among finches to help them adapt to different food sources (e.g., large seeds vs. insects)?
Beak size and shape.
Coastal salamanders adapted using camouflage (blending into forests), whereas inland Sierra salamanders adapted using what type of survival strategy?
Warning coloration / Mimicry (bright colors that mimic poisonous species to deter predators).
In the abundance of known species pie chart, which group makes up over 58% of all documented living species?
Insects (~925,000 out of 1.58 million species)
Look at the vertebrate tree. Why are fish placed at the very base of the tree compared to land vertebrates?
Vertebrates originated with fish in the oceans (~530 mya) before amphibians, reptiles, mammals, and birds evolved onto land.
Why do evolutionary biologists consider a 20-million-year event like the Cambrian explosion to be "short"?
Compared to Earth's 4.6-billion-year history, 20 million years is less than 0.5% of geological time.
What drives natural selection in finch populations during severe droughts?
Birds with beak traits best suited for the remaining food sources survive and reproduce, passing those traits to offspring.
What happens when the two lineages meet again at the southern end of the valley?
They have diverged so much that they can no longer interbreed (acting as separate species)
Contrast speciation and extinction. How do both work together in evolution?
Speciation creates new species, while extinction permanently removes species. Extinction clears ecological space, opening up resources for newly evolved species to diversify through natural selection.