Lecture 11A - Evolution

Question 1

What is Natural Selection?

Answer 1

Natural selection is a process in which inherited variations between individuals cause differences in survival and reproduction.

Question 2

What is the Theory of Evolution?

Answer 2

All species of organisms arise and develop through the natural selection of small, inherited variations that increase the individual’s ability to compete, survive, and reproduce.

Question 3

What is Evolution?

Answer 3

Evolution holds that all species are related and gradually change over generations. In a population, the genetic variations affect the physical characteristics of an organism.

Evolution is an aggregate effect over populations. It’s a process of continuous branching and divergence of populations of organisms.

Question 3

What are the 3 ways theory of evolution explain the phenomena in the natural world?

Answer 3

Adaptation
- Natural selection favours adaptations that best enable creatures to survive under the circumstances in which they live.

Increasing Diversity
- Over time the number of species on earth has generally increased (despite periods of mass extinction).

Increasing Complexity
- The history of life on earth starts with relatively simple life forms, with more complex organisms appearing later in the geological record.

Question 4

How is evolution simulated/modelled - features?

Answer 4

Features to produce evolution:
- Replicator: a population of agents that can reproduce in some way.
○ If it’s a perfect copy it’s a replication
○ If it’s an imperfect copy it’s a mutation (ie children)
- Variation: variability in the population, that is, differences between individuals.
○ Diversity in the population
- Differential Survival or reproduction: The differences between individuals must affect their ability to survive or reproduce.
○ Has the ability to reproduce and survive based on their fitness
○ The agent might live long enough to reproduce
§ If it does not it dies
For modelling evolution the above three mechanisms are sufficient.

Question 5

How is evolution simulated/modelled - basic machinery?

Answer 5

• How to represent the genotype?
  ○ A vector of numbers of zeros and ones for example
  
  • How to setup the fitness value? How to relate it to different genotypes?
  • Which agents will die over generations? How to choose them?
  • How many agents will be reproduced? Which agents will be reproduced?
    ○ Close proximity
    ○ Sexual or asexual, etc

NOTE: IT NEEDS TO BE JUSTIFIED OF WHY ITS DONE

Question 6

What is a Genotype?

Answer 6

• Genotype: the genetic information of each agent that to be copied when the agent replicates.
  ○ A genotype can be represented by a sequence of 𝑁 binary digits (0 or 1), where 𝑁 is a parameter that we can choose.

Question 7

What is Fitness?

Answer 7

Fitness: a quantity related to the ability of an agent to survive or reproduce.

Question 8

What is the Fitness Landscape?

Answer 8

• Fitness landscape: a function that maps genotype to fitness.
  ○ This fitness is the “height” of the landscape. Genotypes which are similar are said to be “close” to each other, while those that are very different are “far” from each other.

Question 9

What is speciation?

Answer 9

• Speciation Generally, a population is considered a species if their genotypes form a cluster, that is, if the genetic differences within the population are small compared to the differences between populations.
  
  • Since locations are represented with arrays of bits, we’ll define distance as the number of bits that differ between locations. To quantify the dispersion of a population, we can compute the mean of the distances between pairs of agents.

Question 10

Extra notes to consider about the model provided

Answer 10

• This model is not meant to be realistic
  
  • Rather, it is a demonstration that the features of the model are sufficient to produce the behaviour we are trying to explain.
  • This doesn’t prove that evolution in nature is caused by these mechanisms alone. But it is reasonable to think that they at least contribute to natural evolution.
  • Similarly, it doesn’t prove that these mechanisms always cause evolution. But the results are robust, i.e. in almost any model that includes these features — imperfect replicators, variability, and differential reproduction — evolution happens.