Download Speciation and types of evolution

Speciation
What’s a species?
A group of organisms that normally interbreed
in nature to produce fertile offspring
What’s speciation?
The formation of a new species
How does speciation happen?...
Step 1- Geographic isolation
A population of a species becomes
physically separated
(E.g. by a lake or mountain).
Step 2- Natural selection
Each population changes over many
generations through natural selection
and mutation.
This results in subspecies populations
that have their own different
characteristics but can still
interbreed.
Step 3- Reproductive isolation
The populations change sufficiently
for them to no longer be able to
interbreed.
->A new species has been produced
(speciation).
What changes might cause
reproductive isolation?
• Change in colour patterns
• Change in mating habits
mates no longer
recognised
• Seasonal differences in mating times
• Changed chromosome that prevents sperm of
one group from fertilising eggs of another
Types of evolution
• Speciation shows us how new species might
arise from a common ancestor.
• Different evolutionary paths have been
suggested:
– Divergent evolution
– Convergent evolution
– Parallel evolution
Divergent evolution
• Divergent evolution is when new forms of a species evolve from a
common ancestor
E.g. The Galapagos Island finches or the geographically isolated
rabbits
• Results in phenomenon known as adaptive radiation where
ancestral organisms become adapted to their new environment and
evolve into new forms suited to the environment
• Figure 3.2.8 What environment would have resulted in the whale?
The bat?
Convergent evolution
• Convergent evolution or convergence occurs when
organisms evolve and develop similar adaptations due to:
– Living in similar environments and habitats
– Having similar lifestyles and food source
• Similar habitats -> similar characteristics selected for -> organisms
that look similar despite having very different genes passed down
from very different ancestors
• These organisms may have analogous structures, specific body
parts that are similar looking.
• Figure 3.2.10
Parallel evolution
• Parallel evolution occurs where related species evolve similar
features while separated from each other
• E.g. Old World monkeys and New World monkeys share many
features because of their common ancestors, apart from their very
different tails
To summarise
• Divergent = common ancestry, different
environments, different organisms
• Convergent = no common ancestry, similar
environments, similar organisms
• Parallel = common ancestry, different
environments, similar organisms