Natural Selection & Evolution Flashcards
All 30 cards in this deck
In which year did Charles Darwin publish On the Origin of Species, and what theory did it set out?
1859; the theory of evolution by natural selection.
Where did Darwin collect much of his evidence, and which animals gave him a key example?
On the voyage of HMS Beagle; the Galápagos finches, whose beak shapes varied with the food available on each island.
What was Alfred Wallace's contribution to the theory of evolution by natural selection?
He independently came to the same idea of natural selection and published jointly with Darwin in 1858; his work on warning colouration gave further evidence.
What is natural selection?
The process by which organisms best adapted to their environment survive, reproduce and pass on their advantageous alleles to offspring.
What impact have Darwin's and Wallace's ideas had on modern biology?
Natural selection is the accepted explanation for the diversity of life; it underpins classification and explains things like antibiotic resistance and pesticide resistance.
True or false? Darwin's theory was accepted by everyone as soon as it was published.
False. Many people rejected it, partly for religious reasons and partly because genes and inheritance were not yet understood, so he could not explain how characteristics were passed on.
What is evolution?
The gradual change in the inherited characteristics of a population over time, over many generations.
What are the steps of evolution by natural selection?
e.g. a population of beetles on green leaves, some green and some brown
- There is variation in the population caused by different alleles — some beetles are green, some brown.
- Those best adapted survive and reproduce; others are eaten or die — green beetles are camouflaged and survive.
- Survivors pass the advantageous allele to their offspring, so it becomes more common each generation — the population becomes mostly green.
How does camouflage increase an organism's chance of survival and reproduction?
e.g. a bittern hidden among reeds
It makes the organism harder for predators to see, so it is more likely to survive, breed and pass on the alleles for camouflage.
True or false? Bacteria become resistant because the antibiotic causes them to change so they can survive.
False. The resistance arises from a random mutation that happens by chance; the antibiotic only selects the bacteria that already have it.
A graph shows the percentage of bacteria resistant to an antibiotic rising year on year. What conclusion can be drawn?
The resistant bacteria have a survival advantage and are being selected for, so resistance is increasing in the population by natural selection — evidence supporting Darwin's theory.
How old is the fossil Ardi, and what do its features show?
4.4 million years old; long ape-like big toe for climbing but able to walk upright, long arms, short legs and a small (chimp-sized) brain.
How old is the fossil Lucy, and what do her features show?
3.2 million years old; arched feet and no ape-like big toe, so she walked upright more efficiently, with a brain slightly larger than Ardi's.
What did Richard Leakey's team discover, and how old were the fossils?
Fossils about 1.6 million years old (Turkana Boy, Homo erectus) with short arms, long legs, human-like feet and a much larger brain (about ).
True or false? Lucy is an older fossil than Ardi.
False. Ardi is 4.4 million years old and Lucy is 3.2 million years old, so Ardi is older.
How did stone tools change over time as humans evolved?
From simple pebble tools chipped to a sharp edge (about 2.5 million years ago), to shaped hand axes (about 1.6 million years ago), to small, complex flint tools such as arrowheads and needles (about 50 000 years ago).
How can stone tools be dated from their environment?
By dating the rock layers (strata) they are found in, or fossils found in the same layer — tools in deeper layers are older.
What is a pentadactyl limb?
A limb with five digits and the same basic arrangement of bones, found in many different vertebrate species.
Why does the pentadactyl limb suggest that bats and cats evolved from a common ancestor?
They have the same bone structure; such a structure is unlikely to have arisen more than once during evolution, so a common ancestor must have had it.
True or false? The pentadactyl limbs of different vertebrates all carry out the same function.
False. They have the same bone structure but different functions, e.g. flying, swimming, running.
Name the vertebrate groups that have pentadactyl limbs.
Amphibians, reptiles, birds and mammals.
Who proposed the three domains classification, and what evidence was it based on?
Carl Woese; genetic analysis, especially comparing ribosomal RNA sequences of different organisms.
Name the three domains.
Archaea, Bacteria and Eukarya.
Why did genetic analysis lead to the five kingdoms being replaced by three domains?
Sequencing showed that the prokaryotes are really two very different groups (Archaea and Bacteria), differing in their genes, rRNA and cell chemistry, so they cannot be one kingdom.
Which organisms are in the domain Eukarya?
All organisms whose cells contain a nucleus — protists, fungi, plants and animals.
How do scientists use gene sequencing to work out how closely related two species are?
e.g. a human and a chimpanzee
- Sequence the same gene (or DNA/RNA) from both organisms.
- Compare the sequences for similarities and differences.
- The more similar the sequences, the more closely related the species and the more recent their common ancestor — human and chimp sequences are very similar.
True or false? Bacteria and Archaea belong to the same domain because both are prokaryotes.
False. Genetic analysis showed they are so different in their genes and cell chemistry that they are placed in two separate domains.
True or false? Fossils provide evidence for human evolution because they show how features such as brain size and walking upright changed over time.
True. Comparing fossils of different ages shows a gradual change in human features, which supports evolution.
Why can natural selection not help a population with very low genetic variation to survive a new disease?
e.g. a population of closely related cheetahs
Few or none of the individuals carry an advantageous (resistance) allele, so very few survive to reproduce and pass it on.
True or false? A population of closely related individuals has a higher risk of extinction than one with high genetic variation.
True. With little variation, it is unlikely that any individual has alleles giving an advantage if the environment changes, so the whole population may die out.