B2.8 - Speciation Flashcards
What does evidence for early forms of life come from?
Fossils.
What are fossils?
The ‘remains’ of organisms from many years ago found in rocks.
Describe 4 ways which fossils can be formed:
- from the hard parts of animals which don’t decay easily
- from parts of organisms that have not decayed because one or more of the conditions needed for decay are absent
- when parts of the organism are replaced by other materials as they decay
- as preserved traces of organisms, eg footprints, burrows and rootlet traces.
Why are there few traces of early life forms left?
Many of them were soft bodied.
How may traces of early life forms have been destroyed?
By geological activity.
What can we learn from fossils?
How much or how little organisms have changed as life on earth developed.
What may extinction be caused by?
-changes to the environment over geological time
-new predators
-new diseases
-new, more successful, competitors
-a single catastrophic event, eg massive volcanic
eruptions or collisions with asteroids
-through the cyclical nature of speciation
How does isolation affect new species?
two populations of a species become separated, eg geographically
How does genetic variation affect new species?
each population has a wide range of alleles that control their characteristics
How does natural selection affect new species?
in each population, the alleles that control the characteristics which help the organism to survive are selected
How does speciation affect new species?
the populations become so different that successful interbreeding is no longer possible.
