Evolution & Natural Selection (2025)

evolution

A change in the chracteristics of a species over many generations

natural selection

the process in which an environmental factor acts on a population and results in some organisms having more offspring that survive to reproduce than others

mutation

A change in a gene or chromosome that is the original cause of variation in living things

common ancestor

An ancestor (distant relative) that two organisms have in common.

adaptation

A characteristic that improves an individual's ability to survive and reproduce in a particular environment.

Variation

differences between individuals within a species. These variations help the organism survive in its environment.

Divergent evolution

When new species evolve from a common ancestor. Over time the two new species will not be able to interbreed, creating two new species. This could be due to geographical isolation or environmental changes.

biodiversity

the number and range of species that exist on Earth or in an ecosystem

selection pressure

the effect of the selective agent on a population

selective agent

an environmental factor that acts on a population during natural selection

species

a group of similar individuals that interbreed only among themselves to produce fertile offspring under natural conditions

Jean-Baptiste Lamarck

inheritance of acquired characteristics
eg. giraffes stretching their necks

Charles Darwin

proposed a process called "Natural Selection"
whereby which species change over many generations.

acquired traits

characteristics or behaviour not genetic or inherited

genetic traits

Characteristics that are encoded in DNA

"Survival of the fittest"

Phrase originated from Darwin's evolutionary theory, to describe the mechanism of natural selection

Fitness

is defined as reproductive success
Not always the strongest, most aggressive (just the best adapted to the environment!)

The Process of Natural Selection

variation, selection, reproducing, adaptation

Speciation

is the process by which one species splits into two or more separate species

The Process of Speciation

1. Variation within the population

2. Reproductive Isolation (Due to geographical or climatic barrier)

3. Natural Selection

Leads to changes that prevents the
groups breeding with each other

What is geographical isolation?

occurs when individuals cannot interact due to separation by barriers, such as bodies of water.

What is ecological isolation?

occurs when individuals inhabit different ecological niches or habitats, preventing interaction.

What is temporal isolation?

occurs when individuals are ready to breed at different times of the day or year.

What is behavioural isolation?

occurs when individuals have different mating behaviours, such as variations in mating calls.

What is structural isolation?

occurs when physical characteristics of individuals vary drastically, preventing breeding.

Types of Isolation

Geographical, Ecological, Temporal, behavioural, structural

Adaptive radiation

a form of divergent evolution in which one ancestral species rapidly gives rise to multiple new species.

hybrids

Offspring of different species

hybridization

The process of creating hybrids

Hybrids cons

often have health problems and are infertile (unable to produce offspring).

What is artificial selection also known as?

Selective breeding

What is the process of artificial selection?

The identification by humans of desirable traits in plants and animals

What is the goal of artificial selection?

To enhance and perpetuate desirable traits in future generations

Selective Breeding Methods

Cross-breeding and Inbreeding

Cross-breeding

Mating individuals with different desirable traits to combine these features in their offspring

Inbreeding

Mating closely related individuals

What is the study of fossils called?

Paleontology

How does the fossil record support evolution?

It shows gradual changes in species over time

What are transitional fossils?

Fossils that show characteristics of two different groups of organisms

What are homologous structures?

Structures with different functions but the same basic structure

What is convergent evolution?

When unrelated species develop similar traits due to similar environments

What is divergent evolution?

When a species evolves into multiple different species over time

How does DNA provide evidence for evolution?

By showing that closely related species have similar DNA

What does molecular evidence suggest about evolution?

Organisms with more genetic similarities share a common ancestor

How does embryology support the theory of evolution?

It shows that embryos of different species look similar in early stages

What is a vestigial structure?

A structure that has lost its original function

Why do some species share similar bone structures?

Because they evolved from a common ancestor

How does biogeography support evolution?

It shows that similar species are found in different locations due to common ancestry

What are analogous structures?

Body parts in completely different species that evolve similarly.

What do analogous structures indicate about evolution?

Different species evolve similar traits to overcome similar environmental pressures.

Who proposed the theory of acquiring new traits due to 'use and disuse'?

Lamarck

What is the concept of transmission of acquired characteristics associated with?

Lamarck's theory

According to Lamarck, what creates a need for certain 'acquired' traits?

The environment

What did Lamarck believe about extinction?

He believed there was no extinction.

What is a key concept of Darwin's theory regarding inheritable traits?

Inheritable traits already exist.

What does Darwin's theory say about the transmission of traits?

Transmission of genetic characteristics.

What does natural selection do to certain traits?

Certain traits are 'selected' by nature because the organism is better able to survive.

What is a consequence of natural selection mentioned in Darwin's theory?

Extinction.

genotype

refers to the genetic material passed between generations

phenotype

is the observable characteristics or traits of an organism.