Chapter 19: Natural Selection & Evolution Flashcards
Evolution is…
…a gradual change in the range of organisms on Earth
New speicies come from existing species and other species die out
Natural selection is…
…the mechanism by which new species arise
The key points:
- Individuals in a species show a wide range of variation.
- This variation is because of differences in genes.
- Individuals with characteristics most suited to the environment are more likely to survive and reproduce.
- The genes that allowed the individuals to be successful are passed to the offspring in the next generation.
Darwin’s travels….
…in 1831, aged 22, a naturalist on HMS Beagle on a five year voyage…
south america, galapagos islands, australia, indian ocean and back
collected fossils, specimens and organisms and observed how they adapted to their environment
Darwin’s controversial thinking?
Noticed how fossils changed across various sediment layers (ie. they were changing over time)…and suggested that lifeforms were continually changing
…contrast to religous ideas: special creation; created onece and not changed since
Darwin’s key observations…
…and the deductions that follow
- Organisms produce more offspring than needed to replace them
- Despite this, stable, established populations tend to remain the smae size
- members of the same species are not identical…living things vary
deductions:
- there is a ‘struggle for existence’…there must be a competition for resources and many must die
- the ones that survive are best equipped or suited to their environment…those less suited will die: IE THE SURVIVAL OF THE FITTEST
Survival of the fittest…
…the best-suited organisms survive to reproduce
The next generations will therefore have more of the type that are adapted to suit the environment and fewre of the less well adapted
NOTE: not physical fitness but biological fitness, ie. how well suited or adapted an organism is to its environment
The Origin of Species, 1859…
….changed forever the way people think about how species arise…
…suggested that humans could have evolved from apes
(he was misunderstood and ridiculed)
Evidence for natural selection…
- there is variation within the species
- changing conditions (selection pressure) favours one form of species (selective advantage)
- the frequency of the favoured form increases under these conditions
- (and less favoured species, decreases)
- the changes are not due to any other factor
Natural selection in the Peppered Moth
& why a good example foe natural selection in action…and follows the five rules for natural selection (see previous card)
Originally, nearly all moths were peppered type…but over 50 years to 1895, in certain areas e.g. Manchester, there were mainly dark moths while peppered moths remained in countryside. Why:
- Camoflage important to help prevent moths being eaten by birds
- Industrialisation: killed lichen on trees that moths liked and darkened trunks with soot
- Dark moths were more camoflaged in sooty trunks…so more dark ones survived to reproduce
- In country, lichen still survived and peppered moth remain camoflaged so didnt have to adapt
Over time, with clean air act to reduce pollution, Peppered moths started to spread to cities again
Natural selection in antibiotic-resistant bacteria…
…mutations happen all the time in living organisms including bacteria.
meaning a mutation could give a bacteria resistance to an antibiotic…meaning the resistant bacteria will survive and reproduce > than non-resistant type…
…given bacteria speed of reproduction…they can build a resistant population v quickly
SO DOCTORS V RELUCTANT TO PRESCRIBE ANTIBIOTICS: USING THEM LESS MEANS SLOWING RESISTANT BACTERIA DOWN
Natural selection in sickle cell anaemia…
Sickle cell amaemia is caused by a mutant allele which affects the formation of haemaglobin in red blood cells.
Causes blood cells to become distorted (sickle shaped) when oxygen around it is low…can be fatal
Carriers show no symptoms…and their cells have a great benefit: they are resistant to malaria and parasite dies before it has time to develop
Natural selection and formation of new species…
…different forms of species emerge from different environments…e.g. same plant in different areas with different water levels: one with less water develops long roots and…over time….ends up being v different
The course of evolution…
- Life began in water
- The first life forms were unicell
- These unicells became more complex as cells acquire orangelles (e.g. mitrochondria & chloroplasts)
- Simple multicellular organims evolved from unicells
- The multicellular organisms became more and more complex…leading to plants, animals, fungi
- Some of these organisms colonised land and evolution of land animals
A niche…
a habitat of an organism and the role of the organism in the habitat. e.g. niche of a camel is that of a herbivore in hot deserts
