Origin of Species - Lecture 3

Question 1

What is life?

Answer 1

○ NASA’s definition: any system that shows Darwinian evolution
○ Involves the flow of matter, energy and information
○ Homeostasis/localised negative entropy

Question 2

Where did life most likely began?

Answer 2

○ Deep sea 3.8-4.2 billion years ago
○ First replicating molecules may have come from proton gradients around alkaline hydrothermal vents

Question 3

What is the RNA world?

Answer 3

Appeared around 3.8 billion years ago and then disappeared

Question 4

What is the earliest life?

Answer 4

○ All DNA life traces back to LUCA (last universal common ancestor)
○ Probably used RNA as enzymes which could copy themselves
○ Amino acids can form spontaneously but they will have been used by life after the RNA world
○ DNA and RNA are very fragile so they need protection (a cell)

Question 5

How can you have a cell without DNA?

Answer 5

○ Tiny pores in rocks around vents
○ Lipid “protobionts” can “reproduce” and metabolise
○ RNA can spontaneously reproduce within them
○ Glucose-phosphate can be metabolised within them

Question 6

What were the first prokaryotes?

Answer 6

○ Methane-producing bacteria
○ O2 levels remained low
○ Cyanobacteria produce O2 which was consumed by methanogenic bacteria
○ Most methanogens died out due to changes (lack of) trace metals in the sea

Question 7

What are eukaryotes?

Answer 7

○ Have a nucleus, mitochondria, chloroplasts (in plants), golgi bodies, sex, phagocytosis
○ 1,000,000 times the volume of a prokaryote
○ Some eukaryotes are multicellular (most lineages are unicellular)

Question 8

What is eukaryogenesis?

Answer 8

○ Happened once around 2 billion years ago
○ Archaebacterium engulfed heterotrophic eubacterium which became mitochondria
○ Was a chance event (not a product of natural selection)
○ Energy provided by mitochondria allows for large complex life
○ 2nd event for plants: autotrophic eubacterium engulfed by eukaryotic plant ancestor

Question 9

What is Ediacaran Biota?

Answer 9

○ Before Cambrian explosion
○ Spriggina: 3cm long worm thing with bilateral symmetry
○ Dickinsonia: Ccan reach up to 1m long and might have had a gut as it has cholesterol stuck in the fossil
○ Rangeomorphs: fractally branched, looked like plants but actually animals
○ Erniettomorphs: modular or quilted

Question 10

What is the Cambrian Explosion?

Answer 10

○ 540-515 million years ago
○ Most of the types of animals we now see first appeared
○ Arthropods, chordates, worms, etc.
○ Soft bodies preserved in Burgress Shale (Canada), China, Greenland, Russia

Question 11

Why is the Opabinia strange?

Answer 11

○ Five eyes
○ 7cm long

Question 12

What are the potential causes of the Cambrian Explosion?

Answer 12

○ Physiological change - dissolved oxygen levels allow active life-style?
○ Geographical change - new sea and new niches?
○ Geochemical change - sea-level changes leads to abundance of trace metals to make exoskeletons?
○ Biological change - increase in zooplankton allows new predators to arise, increasing selection pressure?