Natural Selection, Tree-Thinking, and Population-Thinking

This set of flashcards covers vocabulary and key concepts for Unit 1 Lesson 2, including the differences between typological, population, and tree thinking, and the specific biological mechanisms of natural selection as seen in Darwin's finches.

Typological Thinking

A perspective dominant in western society prior to the $1800\text{s}$ where species are described by an ideal "type" and any variation is viewed as noise or error.

Population Thinking

A biological concept where individuals exist as parts of populations and variation is considered an inherent and important feature of biology rather than noise.

Tree Thinking

The idea that evolution is a process of branching where species are related to one another through ancestor-descendant relationships.

Phylogeny

An evolutionary tree that depicts ancestor-descendant relationships and is used to study the origin of traits and species relationships.

LD50

The dose of a substance required to kill half ($50\%$) of the members of a tested population, serving as an indicator of toxicity and an example of population thinking.

Peter and Rosemary Grant

Scholars who conducted a real-world study on an isolated population of Darwin's finches in the Galapagos to observe natural selection.

El Niño ($1976$-$1978$)

A climatic event in the Galapagos that led to extreme drought, resulting in a lack of food for finches and a subsequent increase in the average beak depth of the surviving population.

Heritability

The proportion of the variation observed in a population that is due to variation in genes.

BMP4 (bone morphogenic protein 4)

A signaling molecule and growth factor; in ground finches, higher levels of its mRNA are associated with larger beaks.

Criteria for Natural Selection

The three requirements for selection to occur: variation in a trait, variation in fitness, and an association between variation in fitness and variation in the trait.

Evolution

Changes in allele frequencies that occur between generations; it requires that traits are heritable so they can be passed to the next generation.

Replicator

The unit of natural selection defined as something that can make copies of itself, such as genes, individuals, populations, or species.

Field Study Heritability Challenges

The difficulty in removing variation caused by the environment is a major factor when trying to estimate the heritability of a trait in nature.