Macroevolution (1)

Question 1

What is macroevolution?

Answer 1

Macroevolution is the change that occurs at or above the level of species over long periods of time. Macroevolution happens on a scale that transcends the boundaries of a single species.

Question 2

What is macroevolution in contrast to?

Answer 2

It is in contrast to microevolution, which refers to smaller evolutionary changes (typically described as changes in allele frequencies) within a species or population.

Question 3

What does macroevolution include?

Answer 3

Macroevolution includes the remarkable trends and transformations in evolution, such as the origin of mammals and the radiation of flowering plants.

Question 4

How easy is it to see macro-evolutionary history?

Answer 4

It is not easy to ‘see’ macro-evolutionary history; there are no first-hand accounts to be read. Instead, history of life is reconstructed using multiple lines of evidence, such as molecular sequencing data, geology, fossils and living organisms.

Question 5

What is Phylogeny?

Answer 5

Phylogeny is the scientific study of evolutionary relationships among species.

Question 6

What is Phylogenetics?

Answer 6

Phylogenetics is the study of evolutionary relationships among groups of organisms which have been discovered through the lines of evidence mentioned earlier.

Question 7

How can Phylogeny be represented?

Answer 7

Phylogeny can be represented in phylogenetic tree, where the trunk and stems are lineages of ancestors, the branching points representing divergences between lineages, and the tips of the branches living species (or extinct species that died without descendants).

Question 8

What is the tree of life?

Answer 8

The tree of life is a metaphor describing the relationship of all life on Earth in an evolutionary context.

Question 9

What are some patterns that are repeated in the tree of life? (4)

Answer 9

1. Stasis/equilibrium
2. Lineage-splitting (or speciation)
3. Adaptive radiation
4. Extinction

Question 10

What does the stasis/equilibrium entail?

Answer 10

Many lineages on the tree of life exhibit stasis/equilibrium, which just means that they don’t change much for a long time.

Question 11

Some lineages have changed so little for such a long time that they are often called ______ . Coelacanths make up a fish lineage that branched off of the tree near the base of the vertebrate clade. Until 1938, scientists thought that coelacanths went extinct 80 million years ago. But in 1938, scientists discovered a living coelacanth. Hence, the coelacanth lineage shows about 80 million years of ____ , it has the same body form.

Answer 11

living fossils

stasis

Question 12

What does lineage splitting (or speciation) entail?

Answer 12

Patterns of speciation and times of speciation can be identified by constructing and examining a phylogeny, i.e. the evolutionary history of a species (or group), especially in reference to lines of descent and relationships among other groups of organisms. The phylogeny might show cladogenesis or anagenesis

Question 13

What is Cladogenesis?

Answer 13

Cladogenesis is an evolutionary splitting event where a parent species splits into two distinct species, forming a clade.

Question 14

What is a clade?

Answer 14

A clade is a life-form group consisting of a common ancestor and all its descendants—representing a single ‘branch’ on the ‘tree of life’.

Question 15

What is anagenesis?

Answer 15

In anagenesis the ancestral species gradually accumulates changes, and eventually, when enough is accumulated, the species is sufficiently distinct and different enough from its original starting form that it can be labelled as a new form - a new species. Note that here the lineage in a phylogenetic tree does not separate. Anagenesis is not often shown in the phylogenies that you will be looking at.

Question 16

Palaeontologists see the role of cladogenesis as more important in evolution to that of anagenesis. Anagenetic trends are often associated with _______ trends, and cladogenetic ones with _______ trends.

Answer 16

micro-evolutionary macro-evolutionary

Question 17

What does the adaptive radiation phase entail?

Answer 17

Adaptive radiation is the burst of divergence from a single lineage to give rise to many new species from a single ancestor. This pattern of macro-evolution, a form of cladogenesis, occurs to fill up new ecological niches as in the case of the finches on the Galapagos Islands. Over time, the organisms that have evolved from the common ancestor adapt and change even further.

Question 18

Examples of adaptive radiation

The fossil record contains many examples of adaptive radiation. (3)

Answer 18

• Some 315 million years ago, the reptiles became truly terrestrial (land-living) as they no longer relied on returning to water for reproduction (as do all Amphibian (frog) species). The development of the amniotic egg - an egg that retains its own water supply and can survive on land – allowed reptiles to breed on land.Once on land they diversified rapidly into the various new terrestrial environmental niches.
• Later a similar, even more rapid burst of diversification gave rise to the birds.
• After the dinosaurs became extinct, there was an explosion of mammalian evolution from 65 to 50 mya with many different species appearing at the same time in the fossil record. This was as a result of climatic change as well as the extinction of the dinosaurs. Suddenly there were many empty niches that could be filled by the adaptable early mammals.

Question 19

What does extinction entail?

Answer 19

Extinction is extremely important in the history of life. It can be a frequent or rare event within a lineage, or it can occur simultaneously across many lineages (mass extinction).

Question 20

How often does extinction occur?

Answer 20

Every lineage has some chance of becoming extinct. Over 99% of the species that have ever lived on earth have gone extinct.

Question 21

What are some trends that appear in macro-evolution? Trends that appear in the tree of life include the following: (3)

Answer 21

• The major trend has been towards increased complexity, e.g. prokaryotes (no nucleus) to eukaryotes (have a nucleus), single-celled protists to multi-cellular organisms, primitive societies to the emergence of human societies and the origin of language.
• Increasing body size, e.g. in horses (see page 202) and increases in body size and cranial capacity during hominin evolution 850cc –> 13 30cc in about 2 million years
• Evolving from marine habitats, then to terrestrial habitats, before evolving the ability to fly.

Question 22

Palaeontologists have observed examples of both _____ and ____ ______ in the fossil record. Both happen, but scientists are trying to determine which pace is more typical of evolution and how each sort of evolutionary change happens.

Answer 22

gradualism

punctuated equilibrium

Question 23

What is gradualism?

Answer 23

This hypothesis puts forward that species evolve gradually by small changes over long periods of time. Darwin put forward this suggestion in his book Origin of Species

Question 24

What is a well-known example of gradualism?

Answer 24

A well-known example of gradualism is the evolution of humans. Instead of fast advancements and spontaneous spurts of rapid evolution humans followed a ‘linear’ pattern of evolution - a pattern of gradual evolution. Although the fossil record is still incomplete, the slow gradual changes in the evolution of Homo sapiens are well documented.

Question 25

____ ___ ____ (1941-2002) was one of the most influential evolutionary biologists of the 20th century and perhaps the best known since Charles Darwin. He made scientists rethink well-established ideas about the patterns, pace and processes of evolution.

Answer 25

Stephen Jay Gould

Question 26

What is punctuated equilibrium?

Answer 26

Punctuated equilibrium refers to the speed at which evolution takes place. According to the theory Gould formulated, punctuated equilibrium, evolution is not gradual as proposed by Darwin.

Question 27

What were Stephen Jay Gould’s findings? (4)

Answer 27

• By studying the fossil record he found long periods of time, sometimes millions of years, where species did not change or changed very little (known as equilibrium). • This alternated with (was punctuated by) short periods of time where rapid changes occurred through natural selection.
• As a result new species were formed in a short period of time (rapidly), relative to the long periods of little or no change
• This is supported by the absence of transitional fossils (often termed ‘missing links’) indicating the period of rapid change.

Question 28

When do phenotypic modifications occur?

Answer 28

Phenotypic modifications occur when species first branch off from the parent species and then change little after that – as long as the environment stays stable.

Question 29

Gould predicted that events such as ___ ___ and _____ impacts created great environmental changes. These sped up evolution because, for species to survive, they would need to adapt quickly to the new environment. Those that did not adapt became ____. This theory is becoming accepted by more and more scientists.

Answer 29

volcanic eruptions
meteor
extinct

Question 30

As an example, a study of fossil snails at Lake Turkana (Kenya) demonstrated that the snails showed __ _____ for very long periods followed by occasional sudden change. These changes were associated with changes in lake levels due to climate change.

Answer 30

no change