Biology 2E: Chapter 18 Evolution and The Origin of Species

Week 4 Evolution Part 1

What is evolution by natural selection?

A mechanism for how species change over time, in which individuals with favorable heritable traits are more likely to survive and reproduce, causing those traits to become more common over generations.

What are Darwin's 4 postulates of natural selection?

1. Individuals vary in their characteristics.

2. Most characteristics are heritable and passed from parent to offspring.

3. More offspring are produced than can survive, causing competition for resources.

4. Individuals that survive the competition reproduce and pass their characteristics to the next generation.

How does variability lead to differences in reproductive success?

Individuals have different traits. If certain heritable traits make an individual better able to survive environmental conditions or competition, that individual is more likely to reproduce and pass those traits to offspring

What are the four types of evidence for evolution?

Fossil record, homologous structures, biogeography, and molecular biology.

How does the fossil record provide evidence for evolution?

It shows that organisms from the past are not identical to organisms alive today, demonstrating that organisms have changed over time.

How do homologous structures provide evidence for evolution?

Similar structures in different organisms can indicate that the organisms share a common ancestor.

How does biogeography provide evidence for evolution?

The geographic distribution of organisms corresponds with Earth's history. Organisms that existed before Pangea separated can be distributed worldwide, while organisms that developed afterward may occur only in certain regions.

How does molecular biology provide evidence for evolution?

Similar DNA sequences among organisms, especially closely related organisms, support the idea that they share common ancestry.

What are the two types of speciation?

Allopatric speciation and sympatric speciation.

What is allopatric speciation?

Speciation that occurs when a population becomes geographically separated into different locations.

What is sympatric speciation?

Speciation that occurs while populations remain in the same geographical area.

Compare allopatric and sympatric speciation.

Both can lead to reproductive isolation and new species. The difference is that allopatric speciation involves geographic separation, while sympatric speciation occurs in the same area.

What are the two categories of reproductive isolation?

• Pre-zygotic: prevents mating or fertilization.

• Post-zygotic: occurs after fertilization.

What are the three types of pre-zygotic isolation?

Temporal, habitat, and behavioral isolation.

What is temporal isolation?

Species reproduce at different times or have different breeding schedules.

What is habitat isolation?

Species are separated by where they live or occur, preventing reproduction.

What is behavioral isolation?

Differences in reproductive behaviors prevent species from mating.

What are the three types of post-zygotic isolation?

Hybrid inviability, hybrid sterility, and hybrid breakdown.

What is hybrid inviability?

An embryo is produced but cannot survive development.

What is hybrid sterility?

A viable hybrid offspring is produced, but it cannot reproduce.

What is hybrid breakdown?

Hybrid offspring reproduce, but later generations have reduced fitness or viability.

Two species reproduce during different seasons. What reproductive barrier is this?

Temporal isolation → pre-zygotic

Two species live in different habitats and therefore do not reproduce with each other. What barrier is this?

Habitat isolation → pre-zygotic

Two species mate and produce an embryo, but the embryo doesn't survive development. What barrier is this?

Hybrid inviability → post-zygotic

A population is physically separated into two geographic locations and eventually forms two species. What type of speciation is this?

Allopatric speciation.