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Flashcards in Evolution 3 Deck (21):

What is 'fitness' linked to?

Linked to environment, not progress.


What will happen if a population doesn't have genetic variation?

The population may still survive but won't evolve much which could lead to the population dying out.


What is macroevolution?

Patterns in change of species composition over gelogical time periods.


What are living fossils?

Some species remain virtually unchanged for millions of years.


Give an example of a 'living fossil'

The coelacanth, Latimeria from the Comoro Islands.

Horseshoe crab


How can the rate of evolution be measured and give an example.

By measuring changes in the size and shape of fossils.
E.g Macfadden measured horses teeth.


What is the formula for measuring the rate of evolution?

r = ln X2 - ln X1 / Δt

r = rate of evolution in Darwins

ln X2 = Natural log of mean measurement of more recent specimen.

ln X1 = Natural log of mean measurement of more ancient specimen.

Δt = Distance apart between specimens in millions of years.


Why must fossil measurements be measured in logs?

Because otherwise the rate of evolution would appear to speed up as structures got larger and different sized animals couldn't be compared.


What is another way of measuring the rate of evolution and give an example.

By measuring changes in the number of structures.
E.g Sheldon recorded the number of ribs on the pygidium of fossil trilobites.


What features should be ,measured on fossils as they evolve?

Non continuous characters.


What is gradualism?

The rate at which new species appear is gradual as well as the rate of evolution.


What are the flaws of gradualism?

Most fossil records don't reflect this - new species appear suddenly.

The result of an incomplete fossil record - intermediates rare.


Explain Eldredge and Gould's interpretation of the fossil record.

Long periods of no evolutionary change (stasis) are punctuated by rapid evolution when speciation occurs.


What is the theory of punctuated equilibrium?

New species arise by splitting off from lineages.

Small isolated populations evolve rapidly.

Sub population gives rise to new species.

New species originates in a very small part of ancestral range so fossils are rare.


Where is there evidence for punctuated evolution?

From lake Turkana in Africa.
Aquatic snails here show little evolution for prolonged periods with occasional bursts of evolutionary change.

Species change when water level rises.

Isolated small populations of snails evolved when water levels were low and the lake was fragmented.


Why do species become extinct?

Predators may kill all their prey.

Parasites may kill all their hosts.

Superior competitors may eliminate inferior ones.

A species food supply may disappear.

Specialists at greater risk of extinction than generalists.

Species that are naturally rare have greater risk of extinction than abundant rapidly reproducing species.

Environmental factors (temperature or water level)


Name the major mass extinctions and when they happened.

Permian/Triassic boundary 225 million years ago mass extinction eliminated 50% of all marine species.

Cretaceous/Tertiary boundary 65 million years ago a mass extinction eliminated 30% of all marine species and the dinosaurs.


What are the 'big 5' mass extinctions?

Ordovician - Silurian

Late Devonian

Permian - Triassic

Triassic - Jurassic



What evidence is there for Cretaceous/tertiary mass extinction?

Iridium found all over world. Rare element in extraterrestrial objects.
65 million years


What evidence is there for a meteor strike?

Crater discovered in 1992 near Chicxulub in Mexico - 65 million years ago.


What geological evidence is found at the crater in Mexico?

Shocked quartz crystals and tektites.