Common Ancestry
Polar bears and brown bears share a recent common ancestor, which means they…
evolved from the same ancestral species
What is a Phylogenetic tree?
A diagram that shows evolutionary relationships between species.
The formation of new species is called…
speciation
A barrier that prevents species from mating or producing fertile offspring is called…
reproductive isolation
What are Homologous Traits
Structures that are similar due to shared ancestry but do different things.
DNA evidence shows polar bears are most closely related to brown bears. This type of evidence is considered the strongest because…
DNA directly reflects genetic similarity and evolutionary relationships
On a phylogenetic tree, a branching point represents…
a common ancestor
Polar bears originally evolved from brown bear populations that became isolated in Arctic environments. This is what type of speciation?
allopatric speciation
Melting ice allows polar bears and brown bears to meet and mate. This reduces…
reproductive isolation
The forelimbs of polar bears and brown bears are homologous because they…
have the same underlying structure from a common ancestor
As Arctic ice melts, polar bears may increasingly interact with brown bears. What does their ability to produce hybrid offspring suggest about their ancestry?
they diverged relatively recently from a common ancestor
If polar bears and brown bears are shown branching close together, what does that indicate?
they are closely related / share a recent common ancestor
If polar bears fail to adapt quickly enough to warming temperatures, what is the most likely evolutionary outcome?
extinction
If hybrid “pizzly” bears are fertile and reproduce, what happens to reproductive isolation between species?
it decreases or breaks down.
Different fur color between polar and brown bears is best explained by…
adaptation through natural selection
Polar bears evolved adaptations like white fur and fat insulation after separating from brown bears. This is an example of…
divergent evolution from a common ancestor
If hybridization continues, how might this complicate building a phylogenetic tree?
gene flow makes relationships less distinct and harder to trace
Explain why increased hybridization due to climate change could prevent full speciation of polar bears.
gene flow keeps populations genetically similar, preventing divergence
Why are homologous traits important when predicting how polar bears might evolve?
they reveal shared genetic potential and evolutionary history
If climate change causes habitats to overlap permanently, what could happen to the genetic distinction between polar and brown bears over time?
gene flow could blur differences, reducing species separation
In a tree including polar bears, brown bears, and black bears, which two would share the most recent common ancestor?
polar bears and brown bears
Predict a long-term outcome: If Arctic ice disappears completely, what evolutionary pressure would most strongly drive speciation in remaining bear populations?
natural selection based on new environmental conditions (diet, temperature, habitat)
If polar bears begin adapting to land environments, which homologous trait might change function over time?
limbs (from swimming to walking/hunting on land)