Download Natural Selection 2

Natural Selection 2
Adaptive Evolution
Natural Selection Leading to Adaptive
Radiation
• Life descends from shared
ancestors
• Changes over time via sexual
reproduction, mutation etc
• Favorable traits are selected for and
therefore become more common in
future generation - this is Natural
Selection
Principles of Natural Selection
• Individuals in the population are different
• Variations are inheritable and can be subject to mutation
• More offspring survive to sexual maturity and reproduce
(causes competition)
• Some individuals have traits that are better suited to their
environment – they have desirable genetic information. More
likely to be passed on to future offspring
Fitness
• Natural selection produces changes over time within
a population
• Natural selection acts on the phenotypes of
individuals, so some will survive and reproduce,
while others will not – this is genetic fitness
• Adaptive radiation comes from natural selection –
mechanism which leads to new populations that are
better suited to the environment
Artificial Selection
• Requires human intervention
• Only organisms with what we
believe to be desirable traits are
allowed to breed
• Leads to establishment of new
populations via artificial selection
Selection Pressures
• Factors that influence the survival of an individual, a
population or a species.
• Competition
– Food, shelter, territories
– Within a species
– With different species for same/similar resources
• Predator-prey relationships
• Sexual selection
– Selection of traits that will attract mates
Sexual Selection
Sexual Selection
• Linked to mating behaviour in animals
• Form of selection where some inherited
characteristics are considered more desirable
• Those possessing these characteristics are
more successful at finding mates
Sexual Selection
• Special characteristics can
sometimes be a hindrance to
animals as energy has to go into
making otherwise useless
appendages e.g. antlers
• Aside from energy cost, mating
displays might attract predators
• Still holds evolutionary advantage
as traits correlate strongly to
genetic fitness
He’s the man
Sexual Dimorphism
• Males and females of the same species have
different appearances or size
Directional Selection
• When individuals at one end of the curve have
higher fitness than individuals in the middle or at the
other end
Stabilizing Selection
• When individuals near the center of the
curve have higher fitness than individuals
at either end of the curve
Disruptive Selection
• When individuals at the upper and lower ends of the curve
have higher fitness than individuals near the middle
• Can create 2 distinct phenotypes
Microevolution
• Small scale changes in gene frequency
• Occurs in a few generations
• Within a species/population
• Small evolutionary changes
• Observable changes
• E.g bacterial resistance to antibiotics
Macroevolution
• Large scale changes to gene frequencies
• Occurs over a long period of time
• At or above the level of species
• Extended microevolution
• Not directly observed
• Fossil evidence
• E.g. reptiles -> birds
Macroevolution – formation of new
species that occupy different niches
Microevolution – formation of subtle
differences within the same speices
Are humans still evolving?
• Yes – increased gene flow leads to greater
heterozygosity in a population which can lead
to health and survival
• Recent gene changes
– Skin pigmentation
– Lactose tolerance
– Breaking down alcohol
– Early reproductive age in some comminities
Questions
1. Define microevolution
2. Define macroevolution
3. Describe one piece of evidence that supports the
idea that humans are still evolving
4. In what way is the modern synthesis of the theory
of evolution different to that proposed by Darwin
and Wallace?
5. Summarise the different processes that can lead to
microevolution