3.2 Flashcards
Theory of Evolution
Describes how species change gradually over many years from ancestral species into entirely new species.
Evolution
Evolution is a gradual change in the genetic character of populations over many generations, achieved largely through the mechanism of natural selection.
Natural Selection
Natural Selection is the gradual evolutionary change that results from genetic variation in each generation. Environment change gives new changes to the species, those that are suited survive, those that are not will not.
How does natural selection happen
- Within a population of one species, there is genetic diversity, which is called variation.
- Due to natural variation, some individuals will be fitter than others.
- Fitter individuals have an advantage and will reproduce more successfully than individuals who are less fit.
- The offspring of fitter individuals may inherit the genes that give that advantage
Individuals with adaptive traits—traits that give them some advantage—are more likely to survive and reproduce. These individuals then pass the adaptive traits on to their offspring. Over time, these advantageous traits become more common in the population.
Through this process of natural selection, favorable traits are transmitted through generations.
Due to the process of natural selection over generations there is a movement towards fitness in the whole population, the environment constantly selecting for the individuals that are best suited to that niche
What does natural selection lead to?
Speciation
Speciation
Speciation is the formation of new species when populations of species become isolated and evolve differently.
Speciation will depend on
Speciation will depended on:
isolation of species:the process by which two populations become separated by
change of environmental
change of gene pool
colonization
This leads to the species adapting overtime and thus speciation. For example a giraffe with a slightly longer neck will be able to reach leaves that others can not. This gives it an advantage and means that this giraffe will be more successful and likely to survive and breed, passing on their genes to future generations.
Speciation can occur gradually via geographic speciation (allopatric) or competitive speciation (sympatric)
But natural selection is not, on its own, sufficient to lead to speciation: isolation is required.
The role of isolation in forming new species
Populations must first become separated, so that genes cannot be exchanged between them (reproductive isolation). If the environments of the isolated populations are different, natural selection will work on each population so that, through evolution, new species are formed.
Isolation of populations can be caused by environmental changes forming barriers such as mountain formation, changes in rivers, sea level change, climatic change or plate movements.
The surface of the Earth is divided into crustal, tectonic plates that have moved throughout
→ This has led to the creation of both physical barriers and land bridges with evolutionary consequences.
Geographic Isolation
When two populations are separated by geographic barriers such as rivers, mountains, or bodies of water.
It is essential in the formation of new species. Without it, interbreeding would cause the genes from two populations to continue to mix and the characteristics of the ancestral species to remain.
Each species develops differently based on the demands of their unique habitat or the genetic characteristics of the group that are passed onto offspring.
How does geographic isolation contribute to the formation of new species?
Geographic isolation happens when a population is divided into two or more isolated groups by physical barriers such as rivers, mountains, or other geographical features. The separation prevents gene flow between the populations, leading to genetic divergence over time. With limited or no interbreeding between the isolated populations, each group undergoes its own unique evolutionary trajectory, adapting to the specific environmental conditions of their respective habitats. This process, known as natural selection, favors certain heritable traits that confer a reproductive advantage or better adaptability to the local environment. As a result, over successive generations, the populations may exhibit distinct genetic variations and phenotypic differences. If these differences become significant enough, the isolated populations may eventually become reproductively isolated from each other, leading to the formation of distinct species through the process of speciation.
Tectonic Plates and Biodiversity:
The earth’s crust is split into sections called tectonic plates
Plate tectonics have created the major mountain ranges of the world and their movement has changed the locations of landmasses and some of the links between land masses → this allows isolation of gene pools and subsequently unique species of plants and animals living on the same land masses. The movement of land masses has also meant that many continents have traveled through different climate zones (over millions of years) which has led to species adaptation and evolution.
Plate Tectonics: the movement of plates → move parallel to, be pushed under or collide with each other.
The movement of plates through different climatic zones allows new habitats to present themselves, and allow for different adaptations.
For example, the separation of Australia led to the preservation of its distinctive flora and fauna (eucalyptus and marsupials such as kangaroos). Similarly, Madagascar is the only place on Earth where lemurs are found today.
Mass Extinction
Mass extinctions of the past have been caused by various factors, such as tectonic plate movements, super-volcanic eruption, climatic changes (including drought and ice ages), and meteorite impact—all of which resulted in new directions in evolution and therefore increased biodiversity.
A mass extinction is defined as a period in which at least 75 % of the total number of species on the Earth at the time are wiped out. We have experienced 5 mass extinctions.
We are currently living through the ‘sixth’ mass extinction according to many scientists. The present rate of extinction of species is thought to be 140 000 species per year. The sixth extinction event is thought to be occurring at a rapidly increasing rate.
The two major causes for the sixth extinction are thought to be human hunting and the rapid rise in human population. As well as occupied territories throughout the Earth, and the development of
agriculture in the last 10,000. Species have been unable to adapt because of the speed of changes on Earth, largely caused by humans.
Pollution and climate change have added to the destruction of their ecosystems.
Although the mass extinction events led to a massive loss of biodiversity, with less than 1 per cent of all species that have ever existed still being alive today, they ultimately led to new biodiversity evolving. The large-scale loss of species led to new opportunities for surviving populations, with many groups undergoing adaptive radiation (where an ancestral species evolves to fill different ecological niches, leading to new species).
Genetic Variation
Within a population of one species, there is genetic diversity, which is called variation.
