Speciation Flashcards
How are fossils formed?
-The most common type is the gradual replacement of the hard parts of animals by minerals.
Process:
Things like teeth, shells, bones which don’t decay easily can last a long time when buried. These are covered by sediment before it is damaged.
Protected, over million the years these become mineralised and they turn into rock. Fossil stays distinct inside of rock.
-Preservation
Process:
When conditions for decay aren’t present, for example there might be a lack of oxygen, poisonous gases or the temperature might be too low. These are not the right conditions for microbes which cause decay.
Another example is in glaciers where it is too cold for decay microbes to work and lastly peat bogs,where it is too acidic for decay microbes to work.
-From casts and impressions
Process:
When organisms are buried in a soft material like clay. The clay later hardens around it and the when the organism decays, it leaves a cast of itself.
Things like footprints can be pressed into these materials when soft, leaving an impressions when it hardens.
An animals burrow or a plant’s roots can be preserved as casts.
Why is the fossil record incomplete?
- Destroyed by geological activity
- Most organisms that died did not fossilise, as conditions for fossil formation were rare
- Many of the earliest forms of life were soft bodied organisms and soft tissue tends to decay away completely. So few traces are left behind.
Many hypotheses speculating how life began cannot be supported or disproved because there’s a lack of valid and reliable evidence.
What does an endemic species mean?
When a species evolves in isolation and is found in only one place in the world, it is said to be endemic to that area.
What is extinction?
Extinction is the permanent loss of all members of a species.
What causes extinction?
- NEW PREDATORS
- Prey animals are wiped out by predators very quickly because the prey animals do not have the adaptations to avoid them.
- New predators might be introduced when an existing species moves into an existing territory through human intervention.
- NEW DISEASES( caused by microorganisms)
- Don’t have genes or alleles to give them resistance. They are most likely to cause extinction in islands, where the whole population is close together so the spreading of infectious diseases is more likely.
SUCCESSFUL COMPETITION
*New mutations can give one type of organism a real advantage over another. They eat and breed so fast that the other animal can’t survive.
CATASTROPHIC EVENT
*For example an asteroid can desimate a population
ENVIRONMENTAL CHANGE
*Not adapted to survive the conditions, might be too hot or too cold for them to survive.
CYCLICAL NATURE OF SPECIATION.
What are fossils?
Fossils are the remains of organisms from many thousands or millions of years ago that are going preserved in rocks. They show how an organism has changed over time.
What is a species?
A species is a group of organisms which can interbreed to produce fertile offspring.
What is speciation?
The development of a new species due to isolation and natural selection. Speciation occurs when populations of the same species become so different that they can no longer breed together to produce fertile offspring.
What is isolation?
Isolation is where populations of a species are separated. This can happen due to a physical barrier, like floods and earthquakes which can cause barriers that geographically isolate some individuals from the main population
Describe how isolation and natural selection leads to speciation.
Species become separated through a physical barrier( e.g floods). These barriers geographically isolate some individuals from the main population.
Conditions on either side of the barrier will be slightly different( different climates). Because the environment is different in each side, different characteristics will become more common in each population due to natural selection.
There will be genetic variation in each population because they have a wide range of alleles. In each population, individuals with characteristics that make then better adapted to the environment have a better chance of survival and so are more likely to breed successfully.
So the favourable alleles that control the beneficial characteristics are more likely to be passed on the next generation.
Eventually, individuals from the different populations will have changed so much that they won’t breed with one another to produce fertile offspring.
