Unit 7 Natural Selection

Charles Darwin

Father of evolution who published On the Origin of Species that presented theories such as natural selection causing “descent with modification”.

Evolution

process by which species change over time through the gradual accumulation of genetic variations

Natural Selection

process by which individuals with traits better suited to their environment are more likely to survive and reproduce.

fitness

an organism’s ability to survive and reproduce in a particular environment.

adaptations

advantageous traits inherited through natural selection.

Selective Pressures

predators, climate, competitions for resources are all examples of what?

Heritable Variation

Within a population, individuals vary in their heritable traits.

Overproduction of Offspring

Most species produce more offspring than can survive to adulthood, which leads to a competition for resources.

Artificial Selection

humans selectively breed individuals with desirable traits to produce offspring with those traits.

Population

a group of individuals of the same species that live in the same area and interbreed, sharing a common gene pool

gene pool

the total collection of alleles in a certain population.

Fixed alleles

all members of the population are homozygous for a certain allele

Microevolution

small-scale evolution that occurs within a species over time

Mutations

random changes in the DNA sequence that can introduce new alleles into a population - can have a good, bad, or no effect on survival and don’t always lead to evolution

Genetic drift

random fluctuations in allele frequencies, particularly in small populations, due to chance events.

Founder effect

when a small group of individuals breaks away from a larger population to form a new, less diverse population.

Bottleneck effect

When a large population is drastically reduced in size due to a sudden event, such as a natural disaster

Gene flow

also called migration - the transfer of alleles between populations, which can introduce new genetic material into a population.

Phenotype

Does natural selection act on phenotypes or genotypes of organisms?

Directional

Favors one extreme phenotype, causing the allele frequencies to shift in one direction

Stabilizing

Favors the average phenotype, reducing variation in the population

Disruptive

Favors extreme phenotypes at both ends of the spectrum, increasing variation and potentially leading to speciation

Sexual

individuals with traits that are attractive to the opposite sex have a higher chance of reproducing, which can lead to the evolution of traits that improving mating success but not survival

Hardy-Weinberg Equilibrium

mathematical equation that predicts the frequencies of genotypes in a population. It tells us if natural selection or other factors are causing evolution at a particular locus.

equilibrium conditions

No mutations

Random mating

No natural selection

Extremely large population size

No gene flow

Radiometric Dating

Carbon-14’s predictable decay rate allows scientists to estimate the age of organic materials.

Rock layers

the relative positioning of fossils within layers of sedimentary rock

Transitional fossils

show intermediate traits between ancestral and modern forms, highlighting evolutionary changes over time

Comparative Morphology

examines the similarities and differences in the physical structures of organisms.

Homologous structures

anatomical features that share a common evolutionary origin, even if they serve different functions in modern species

Embryonic homology

similarities in embryonic development across species suggest a shared ancestry.

Vestigial structures

remnants of features that served important functions in ancestors but are now reduced or unused.

Molecular homology

DNA and protein sequences reveal evolutionary relationships

Analogous structures

unrelated species independently evolve similar traits due to similar environmental pressures, not shared ancestry.

convergent evolution

Analogous structures are an example of?

Cellular

all eukaryotes share membrane-bound organelles, such as nuclei and mitochondria from shared evolutionay origins

chromosomal

linear chromosomes and introns in genes are shared features of eukaryotic cells from shared evolutionary origins.

Biogeography

the study of the geographic distribution of species

Continental drift

the movement of tectonic plates explains how closely related species can be found on continents that are now far apart

Endemic species

found in specific locations and nowhere else, highlighting the role in isolation in evolution.

Species distributions

distribution of species often aligns with their evolutionary history

Phylogeny

the study of evolutionary relationships among species with a crucial aspect of systematics and taxology

phylogenetic trees

diagrammatic representations of the evolutionary history of organisms.

Lineage

A sequence of species that have evolved from a common ancestor

Node

A branching point representing a common ancestor

sister taxa

two groups that share an immediate common ancestor

Basal taxon

a lineage that diverged early in the history of the group

Ancestral

traits that were present in a common ancestor

derived

traits that have evolved more recently

synapomorphy

a shared derived characteristic that can be used to define clades

in-group

the group of organisms under study

out-group

a distantly related group of organisms to the organisms under study.

Cladograms

a type of phylogenetic tree that focuses on the relationships between organisms based on shared derived characteristics

principle of parsimony

the scientific principle that things are usually connected or behave in the simplest or most economical way, especially with reference to alternative evolutionary pathways.

Speciation

The process through which new species arise

Allopatric

occurs when populations of a species become geographically isolated from one another

prezygotic barriers

isolation prevents mating or fertilization between species

habitat

species live in different habitats and rarely encounter each other

temporal

species breed at different times

behavioral

differences in mating behaviors prevent species from recognizing each other as potential mates

mechanical

structural differences in reproductive organs prevent successful mating

gametic

even if mating occurs, the sperm and egg may not be compatible

Reduced hybrid viability

Hybrid offspring may not survive to maturity

Reduced hybrid fertility

hybrids may be sterile and unable to reproduce

Hybrid Breakdown

Offspring of hybrids my be fertile, but their subsequent generations are inviable or sterile

Postzygotic barriers

occur after fertilization: reduced hybrid viability, reduced hybrid fertility, hybrid breakdown

sympatric

occurs when mechanisms such as polyploidy lead to a new species that can only breed among themselves.

punctuated equilibrium

species remain relatively unchanged for long periods and experience rapid bursts of change

gradualism

species evolve slowly and steadily over time.

divergent

related species develop different traits

adaptive radiation

a single ancestor species rapidly diversifies into a range of forms to exploit different niches

convergent

occurs when unrelated species evolve similar traits to adapt to comparable environments.

4.5

Earth formed approximately ___ billion years ago

3.8

about ___ billion years ago conditions on Earth became suitable for life

Stromatolites

layered structures created by the activity of micro-organisms

cyanobacteria

played a significant role in shaping Earth’s early atmosphere by producing oxygen through photosynthesis

hydrothermal vents

___ and lightning strikes may explain the transition from inorganic to organic molecules

Oparin and Haldane

hypothesis that proposed that Earth’s early atmosphere was rich in compounds like methane, ammonia, and hydrogen, which could react to form organic molecules

Miller-Urey

experiment simulating earth’s early conditions by administering electrical shocks to a mixture of gasses, which formed amino acids.

RNA world hypothesis

theory that suggests that early life forms may have relied on RNA to store genetic information.

ribozymes

supporting the RNA world theory, molecules that can catalyze chemical reactions