Darwin and the Rate of Evolution

Idea before Evolution: Innuits

land rose out of the water and a raven secured this floating land by stabbing its beak in it

Idea before Evolution: Ancient Egypt

interaction between water, air, darkness and eternity, the god Ra rose from a blue lotus flower

Idea before Evolution: Literal interpretation of the bible

human were specially created, that all life is young and humans were separate creations

Argument from Design - William Paley

• 1800

• there must be a designer for Earth and its design is related to its function

Who suggested Natural Selection before Darwin and what was their idea?

• 1831

• Patrick Matthew

• Naval Timber and Arboriculture

• idea not noticied

Why did Darwin wait so long to release Origin of Species?

• his wife was very religious

• he was originally planning Natural Selection (massive book) but was rushed to released the idea after Alfred Russell Wallace also made the same observation

How with The Origin recieved?

• many were surprised

• Thomas H. Huxley was surprised he didn’t come up with the idea himself

• Some were sceptical

• Huxley become Darwin’s biggest supporter

Two Main Issues with Natural Selection

1. Is natural selection compatible with the nature of inheritance

• at various times considers wrong models

• blending inheritance and natural selection were not compatible

2. Is the earth old enough?

• people were sceptical if the earth was old enough to be consistent with Darwin’s mechanism

How old is the Earth?

• Darwin, consulting with geologists, through it was 300 million years

• William Thomson believed he could destroy Darwinian evolution by showing Earth was too young

How did Thomson calculate a Young Earth?

• earth started out as molten

• knowing its size and the current rate of heat loss from the surface, you can calculate the age since the molten state

  • heat gradient known from mines: one degree every 50 feet

• assumes no unknown source of energy

• came up with 20-40 million years

Why was Thomson so wrong?

• he didn’t know about radioactive decay

  • discovered by the Curies

• dating could be done accurately

• radioactivity makes a huge effect on the age of the sun

• missing calculation: lack of convection in the upper mantle

• new calculations: around 2 billions years

Fishers Fundamental Theorum

Evolution should go faster if there is strong selection and lots of variation

• change in fitness from one genertion to the next should be equal to the variance in fitness

• if there is no variation then fitness cannot increase as selection cannot operate

• if there is lots of variation, then selection can eliminate the least fit and preserve the most fitn

• if there is lots of variation, but selection doesn’t care much the variation, then evolution should be slow

Current estimate for age of earth

• 4.5 billion years

• earliest fossil evidence is 3.5 billion evidence

• earliest eukaryote: 1.8 billion years

Example of Fast Evolution: Wing size in fruit flies

• Europe: a cline running north south in wing length

• North America: no wing length cline after one decade

• rate of morphological evolution on a continental scale is very fast, relative even to rates measured within local populations

Example of Fast Evolution: Cod since WWII

• 1950s: took 10 years to mature and spawn at same site

  • would hang around in feeding grounds

  • produced many offspring

• Since WWII: rise in use of industrial motor powered fishing boats

  • make it possible to catch in feeding grounds

  • selection favoured those that breed earlier and do not grow as large

  • mean age of spawning has decrease

Example of Fast Evolution: Sticklebacks

• studied stickleback fish in 3 isolated coastal lakes

• each lake independentlz evolved two non-interbreeding forms

  • bottom dwelling

  • open water limnetic fish

• fish originated from a single marine ancestor trapped in lakes formed years ago

• mating tests showed females prefer males that resemble themselves

• reinforced reproductive isolation

Example of Fast Evolution: Salmon

• studied introduced salmon populations in Canada

• two adjacent populations share a common ancestry but breed in different environments

  • a river

  • a lake beach

• using DNA microsatellites, natural tags, and phenotypic traits, researchers tested for reproductive isolation

• evidence showed reproductive isolation evolved in fewer than 13 generations

• this demonstrates that speciation can occur extremely rapidly and be linked to adaptation to new environments

How do we calculate s from the rate of spread of an allele?

Using computer:

• calculate successive gene frequencies and work out, for a given s, what the gene frequency would be after the known number of generations

• if the value obtained is higher than actually found we repeat the process with a lower value of s

• if too low we can increase the value of s

• we can converge on the value of s