Lesson 8: Evolution

Question 1

What was Charles Darwin’s theory?

Answer 1

explains how new species come into existence, how organisms become adapted to their environments, and why specific groups of organisms share specific traits

it also correctly postulated that all life on Earth is related and shares a single common origin

Question 2

What are heritable traits?

Answer 2

heritable means that the trait is part of an organism’s genetic code and, therefore, either will be, or (depending on the type of reproduction) has a chance to be, copied to the organism’s offspring

heritability is the reason that sons and daughters tend to resemble their parents

a trait must be heritable in order for that trait to evolve

Question 3

What is variation?

Answer 3

sometimes organisms have heritable traits that are new, not copied from the organism’s parents

one source for new heritable traits is random genetic mutation

in order for selection to occur on any given trait in a population

Question 4

What is an advantage?

Answer 4

an organism’s traits affect how successfully that organism is able to reproduce

often, a trait’s effect is indirect, that is, it improves or hinders an organism’s ability to survive, which, in turn, affect how many reproductive opportunities the organism has

one variation of the trait must provide an advantage (or, differential success) over the other variations in order for evolution to occur

Question 5

What is competition?

Answer 5

natural environments have limited resources, and competition for these resources permits only some organisms to successfully reproduce before they die

some of the versions of a given trait must be “selected out” of a population in order for evolution to occur, and this must occur because of competition for limited resources

Question 6

What is the theory of evolution?

Answer 6

the differential success of certain variations of a heritable trait, because of competition for limited resources, leads to the change over time (evolution) of the trait in a population

Question 7

How does the evolution of a species not require the extinction of its ancestor?

Answer 7

for instance, a new species might simply branch off from an ancestral species if only a single population of the ancestral species was exposed to new environmental conditions that favored new traits

while the population in the new environment would acquire new traits better adapted to that environment and evolve into a different species, the ancestral species might continue to exist in its ancestral environment

Question 8

Why is evolution not random?

Answer 8

while new traits may be introduced by random mutations, the determination of which traits are successfully passed on to later generations is not random

instead, it is based on a specific criterion: how well each trait improves an organism’s reproductive success

Question 9

What is natural selection?

Answer 9

the competitive selective process by which detrimental traits are competitively discarded and advantageous traits are retained

Question 10

What are shared common ancestors?

Answer 10

organisms are grouped together based on their most recent shared common ancestors

Question 11

What is the shared common ancestor of all dinosaurs?

Answer 11

all dinosaurs are classified together in a group because as dinosaurs evolved from a single species of amniote tetrapod

within the dinosaurs, all ornithischians are classified together because they evolved from a single particular species of dinosaur, while saurischians are classified together in a different group because they evolved from another particular species of dinosaur

Question 12

What is a character?

Answer 12

is any heritable trait that can be described and labeled

Question 13

What is a shared derived character?

Answer 13

a character that is present in two or more groups and their common ancestor, but is not present in any more distantly related groups

Question 14

What is a synapomorphy?

Answer 14

a shared derived character

Question 15

What is an example of a synapomorphy in dinosaurs?

Answer 15

all species of ornithischians have a special bone in the lower jaw that forms a beak, called the predentary, and no other dinosaurs have this special beak bone

thus, the character of the predentary was passed on to all ornithischians from their ancient shared ancestor and is a synapomorphy that testifies to this shared ancestry and can be used to define the group

Question 16

What is convergent evolution?

Answer 16

the evolution of similar traits in two different lineages

Question 17

What is parsimony?

Answer 17

the idea that “all other things being equal, the simplest answer is usually the right one”

also referred to as Occam’s razor

Question 18

What are phylogenetic trees?

Answer 18

to determine the evolutionary relationships between large numbers of species, many of which may be closely related, and to take into consideration a large number of characters, paleontologists use computer programs

these programs analyze a list of characters that is first compiled by the researcher

this list is called a character matrix

based on the character matrix, the computer program applies the principle of parsimony to arrange the organisms in a sequence of relationships that requires the fewest instances of convergent evolution

the resulting arrangements look like diagrams of a “family tree” and are called “phylogenetic trees”

Question 19

What is a node on a phylogenetic tree?

Answer 19

a node is where two branches diverge, and shows the point at which two linages shared a common ancestor

after a node, the pattern of subsequent branches and nodes shows how the descendants of that common ancestor continued to diverge from each other

Question 20

What is a clade?

Answer 20

a group of species that share a common node

clades can be very small, or very large, there are no size limits

a clade must contain the ancestor of a group and all of its descendants

a group that does not include all of the descendants of a common ancestor is therefore not a clade

Question 21

Who was Thomas Henry Huxley?

Answer 21

a close colleague of Charles Darwin and one of the earliest advocates for the theory of evolution

Huxley was also the first scientist to recognize that birds evolved from dinosaurs, and he cited the newly discovered specimens of Archaeopteryx as fossils of a “missing link” between dinosaurs and birds

showed that transitional forms do exist in the fossil record, just as the theory of evolution predicted, and also showed that birds are a branch of the dinosaur family tree

Question 22

What were the characteristics of the dinosaur Sinosauropteryx?

Answer 22

was the first non-avian (non-bird) dinosaur to be discovered with feathers

the feathers had a simple structure compared to the feathers of modern birds and were used for insulation, not for flight, but they were feathers just the same

many other small theropod specimens have since been found with feathers, some with complex flight feathers

Question 23

How are birds related to dinosaurs?

Answer 23

birds are the only clade of dinosaurs alive today

birds can be classified as theropod dinosaurs, because they evolved from theropod dinosaurs

Question 24

How are birds classified?

Answer 24

many paleontologists use Aves to refer to the crown group of birds, which includes all living birds as well as extinct taxa like the dodo and moa

another clade name, Avialae, is generally equivalent to “flying dinosaurs”, which includes extinct species that looked very similar to modern birds, including Archaeopteryx