Evolutionary Biology (Gareth Jenkins 10-15)

Question 1

What three characteristics must something have in order to be classed as ‘Life’?

Answer 1

• Has a replication potential (heterotrophs Vs autotrophs)
• Have catalytic proteins
• Ability to store, transmit and express information (DNA/RNA)

Question 2

What was significant about Miller’s (1953) experiments?

Answer 2

He produced amino acids and compounds like hydrogen cyanide & formaldehyde, which underwent further reactions to form nucleotides. The conditions he used were synonymous with the conditions of early Earth as described by the Oparin-Haldane theory.

Question 3

What is the general idea of the Oparin-Haldane theory?

Answer 3

Organic molecules accumulated in a prebiotic soup, after being synthesised in a highly reducing atmosphere, when exposed to an external energy source like UV or lightening.

Question 4

What is the significance of clay minerals in supporting the Oparin-Haldane theory?

Answer 4

a criticism is that hydrolysis in a ‘soup’ environment would be too high for polymers of significant length to form. Clay minerals provide an environment where hydrolysis would be reduced.

Question 5

Discuss why hydrothermal vents in the deep sea may have been the site for the origin of life.

Answer 5

The chemicals used in Miller’s experiments are also present in alkaline hydrothermal vents. UV may have been too harsh for life, so this may have been the alternative. Pores in the serpentine rock are ideal environments for the synthesis of organic molecules. Carbon may have been fixated on CO2 and methane-rich emissions; modern-day autotrophs found in these environments exploit this system.

Question 6

Explain the theory of Panspermia.

Answer 6

Life originated extra-terrestrially.
- microbes potentially ejected from their homeworld by impacts may have been carried through space on debris and fallen to Earth in a second impact event.
McKaye et al 1996: found bacteria-like fossils on a meteorite from Mars.

Question 7

What is LUCA?

Answer 7

The last universal common ancestor of all life.

thought to be a type of cyanobacteria (lead to photosynthesis? and therefore the evolution of aerobic respiration?)

Question 8

Advantages of sexual reproduction?

Answer 8

• guards against the accumulation of deleterious mutations.
• creates variation
• can change genomes faster to keep up with ever-changing challenges

Question 9

Disadvantages of sexual reproduction?

Answer 9

• recombination can destroy adaptive complexes of genes.

- half of the offspring are male, so halves the reproduction rate of an asexual genotype.

Question 10

When did the Cambrian explosion begin and why was it important?

Answer 10

• started 543mya
• a major increase in the abundance of skeletal fauna
• the appearance of Crustacea, annelids, Mollusca, Vertebrata etc.
• Very rapid
• The first sign of this kind of life in the fossil record.

Question 11

What is the significance of the Burgess Shale?

Answer 11

in 1909, Charles Walcott discovered exceptionally preserved fossils of benthic, marine fauna, which has been buried in anoxic mudstone. Even soft tissues were recorded due to the fine sediment.

Question 12

What do molecular clocks suggest about the existence of precambrian fauna?

Answer 12

molecular clocks suggest that many clades diversified much earlier than the Cambrian ‘explosion’ but there are just no known fossils.
It was probably an explosion of forms, not lineages.

Question 13

What could have caused the Cambrian Explosion?

Answer 13

• Increased O2 availability?
  - would have lead to faster metabolism and larger size.
  - larger size required for the evolution of tissues and high metabolism for movement.
  - motility = new niches, adaptations to new food sources (mouths and guts) and there would also be increased predator-prey diversity due to coevolution.

Question 14

What are Hox genes?

Answer 14

They evolved with multicellularity and carry information about cell arrangement.
They regulate transcription of other genes and proteins and control animal development by producing chemical gradients.

e.g. in lobopodians, maxillipeds form where Hox7 is expressed.

Question 15

Which 2 patterns of evolution are found in the fossil record and may explain the diversification in the Phanerozoic?

Answer 15

Punctuated Equilibrium: periods of rapid change followed by long periods of stasis.

• Involves peripatric speciation
• ancestral species must coexist with the new species.

Phyletic Gradualism: morphospecies occur sequentially.
-evolution of ancestors without speciation (anagenesis)

Question 16

Give an example of Phyletic gradualism and Punctuated equilibrium.

Answer 16

Phyletic gradualism: in foraminiferan, 4 morphospecies occur in the fossil record sequentially, they show a gradual change over time.

Punctuated Equilibrium: morphological change and speciation in Bryozoa.
- 19 living fossils existing at the same time.

Question 17

What does the rate of background extinction suggest?

Answer 17

The probability of a family or class going extinct is more or less constant but varies between taxa.

(responsible for 96% of all extinctions)

Question 18

What is thought to have been behind the Terminal Ordovician mass extinction?

Answer 18

The glaciation of the south pole

• alternating glaciation and interglaciation episodes caused repeated regressions and transgressions of sea level.
• O2 poor water from deep oceans flooding coastal areas during transgressions.

Mainly affected benthic and planktonic species.

Question 19

What is thought to have been behind the Late Devonian mass extinction?

Answer 19

a series of pulse events over 1my.

• global oceanic anoxia confirmed by the presence of black shales; organic-rich sediments characteristic of anoxic conditions.
• Global cooling possibly due to asteroid/comet impacts- but this is controversial as the timescales don’t quite add up
• mostly affected huge Devonian reefs. Cool water species survived, possibly because they were tolerant due to the previous mass extinction.

Question 20

What is thought to have been behind the End Permian mass extinction?

Answer 20

Formation of Pangaea and Siberian traps:

• a huge reduction in continental shelves
• large-scale changes to heat, CO2 and SO2 atmospheric levels.
• reduced oceanic circulation= anoxia.
• huge land mass = seasonality and weather extremes.
• direct temperature change wouldn’t have caused such a huge wipeout; melting of ice sheets released huge amounts of methane.
• Also evidence of huge coal deposits being ignited by the traps, increasing CO2 further.

Question 21

What is thought to have been behind the End Triassic mass extinction?

Answer 21

• cause not totally known
• involved huge sea level fall and anoxic conditions, perhaps due to volcanic activity in the central Atlantic magmatic province (CAMP).

Question 22

What is thought to have been behind the Cretaceous-Palaeogene (Cretaceous- Tertiary/K-T/ K-P) mass extinction?

Answer 22

Meteorite impact- Chicxulub around 65mya.

• iridium layer/ shocked quartz/ microtektites (glass particles)
• lead to acid rain, earthquakes and eruptions, wildfires, an enormous tsunami (Texas sandstone bar), cooling from dust clouds and blocking of photosynthesis.

Question 23

Why is the K-P extinction thought to be very important for mammals?

Answer 23

The decline of the dinosaurs made way for new ecological opportunities, producing the rise of the mammals?
-long-fuse model best supports this (diversity already exists but thrives under new opportunities)

Question 24

Species can be described as endemic, cosmopolitan or disjunct, what do these mean?

Answer 24

Endemic = limited to a certain area
Cosmopolitan = found on all continents (strictly speaking it includes Antarctica but pigeons are considered cosmopolitan)
Disjunct = not confined to a certain area but distributed in more than one region with a gap.

Question 25

What is the difference between a fundamental niche and realised niche?

Answer 25

Fundamental niche = where the conditions are right and an organism could theoretically live there

Realised niche = niche occupied in the presence of competing species.

Question 26

In the late Jurassic, what did Pangaea split into?

Answer 26

Laurasia (north) and Gondwanaland (south)

Question 27

What is Wallace’s Line?

Answer 27

A faunal boundary line that separates the ecozones of Asia and Wallacea, a transitional zone between Asia and Australia.
Fauna of New Guinea is more similar to Australia than Borneo.

Question 28

What are the three Milankovitch cycles?

Answer 28

Eccentricity (96,000y)
Obliquity (40-41,000y)
Precession (19-23,000y)

can cause Glaciation and Interglaciation

Question 29

How does Post Glacial Recolonisation increase species diversity?

Answer 29

During an Ice age, hedgehogs and bears (for example) migrated to the Balkans and Italy. Theses surviving populations are called refugia, and they evolve genetic differences to other isolated populations. When the ice cap retreats and the populations mix again, reproductive barriers may have formed.

Question 30

What does the Kin Selection theory predict?

Answer 30

that parents should invest considerable time into their offspring as they continue the existence and spread of genes. (e.g. infanticide in lions and many primates)

Question 31

How may stepchildren be treated differently due to biology?

Answer 31

Daly & Wilson:

• stepchildren 70X more likely to be killed
• Risk of lung cancer from smoking is also 11% higher

1988 Trinidad study:

• fathers get on better with and spend more time with their biological children.
• step-father relationship is better if the child is born before the father joins the family.

Flinn & England 1995:
- stepchildren more days ill and have lower reproductive success later in life.

Question 32

Explain how a better understanding of human evolution may change how we treat medical issues as an example.

Answer 32

Pregnancy sickness may be an adaptive trait, protecting women from eating foods that contain chemicals that may harm the embryo.

• Occurs in the first trimester of pregnancy, when the embryo is most vulnerable.
• women who experience pregnancy sickness tend to have lower rates of miscarriages and fewer birth defects of offspring. BUT, This could be due to low levels of chorionic gonadotrophin.
• Taking medicine to suppress pregnancy sickness may lead to more consumption of harmful foods and a higher risk of miscarriages and birth defects.

Question 33

What is Negative Assortative Mating?

Answer 33

suggests that people with highly dissimilar major histocompatibility complex (MHC) genes are more attracted to each other.

• a similarity in MHC genes may increase infertility and miscarriages.
• A diversity of MHC genes may provide greater defences against pathogens.

(Note the sweaty t-shirt experiment)

Question 34

If homosexuality is of genetic predisposition, how can it evolve?

Answer 34

• Kin selection: help raise kin for longer and increases the survival of relatives.
• Overdominance: heterozygote advantage? homozygotes would be gay, but heterozygotes may be more attractive to females.
• Sexually antagonistic selection: allele costly in males, counterbalanced by being a fitness advantage in females?

Question 35

What is the adaptive hypothesis for Menopause?

Answer 35

• human children are dependant on mothers for many years after weaning.
• a woman’s chance to have a baby declines ( increased risks, her daughters will start reproducing etc)
• Women may reach an age where the chances of propagating their own genes are maximised by ceasing reproduction and helping to rear the children of their daughters.
• maternal grandmothers improve the nutritional status of children in rural gambia.
• If menopause is adaptive then taking oestrogen supplements may be creating conditions which the woman’s body may not be designed to cope with.

Question 36

Give an example of unintelligent design in humans.

Answer 36

testes have descended via evolution but the vas deferens still loops unnecessarily.