Two islands of finches, long apart, now with birds crossing between them. Three genes: one for beak size, one for colour, one for the colour a female likes. See whether a difference in what the females like helps the two islands' beaks stay apart.
Click the seeds in the Target card to set how many of each island's seeds are hard. Small beaks crack soft seeds, large beaks hard ones.
Preference strength, the arrow from preference on the diagram, sets how much a female favours a male of the colour she likes.
Fitness surfacesLeft, from the seeds: across, the beak gene (○ two small-beak alleles, ◐ one of each, ● two large); up, a young bird's chance to live to breed on each island. A small beak eats soft seeds, a large beak hard ones, ◐ either, poorly.Right, from the preference strength: across, male colour (dull, in between, bright); up, female preference (the colour she likes). Darker: a higher mating probability when they meet.Circles: run 1's birds (left) and this generation's pairs (right), the bigger the more of them.
Genes, traits, reproductionThree genes, each with two alleles, on different chromosomes: beak (small, large), colour (dull, bright), preference (likes dull, likes bright). A bird with one allele of each is in between. The colour shows in males.Seeds: each island's, set in the Target card. A beak suited to them lives more.Mating: a female meets up to 4 males in turn; the mating surface shows the probability that a meeting ends in mating. If none of the 4 does, she does not breed this year.Preference strength, the arrow from preference onto colour → mating: how fast the mating probability falls as his colour moves away from the one she likes. Colour → mating follows it: dashed at 0, where his colour makes no difference to mating. Grey arrows: fixed.
Target100 birds an island, 1 in 10 swapping islands each generation. The islands start apart: the orange island's birds small-beaked, dull and liking dull; the blue island's large-beaked, bright and liking bright. Go plays 100 generations, 16 times.The picture: what a hit looks like; the red box, where the thick line, the 16 runs' average, should end.Under it, each island's four seeds: click one to set how many are hard; the 0 clears them.
To finish
Hit the three targets. 0 of 3
Stage B is open.
R code
B
Finish Stage A to unlock this section.
One island now, with no birds crossing. Every female likes bright males, and a bright male is likelier to die. See where the colour settles when one arrow pays for it and the other charges for it.
Preference strength, the arrow onto colour → mating, sets how much a female favours a brighter male. Cost of brightness, the red arrow, sets how much likelier a bright male is to die.
Fitness surfacesLeft, from the cost of brightness: across, a male's colour (0, ¼, ½, ¾ or all of his four colour alleles bright); up, his chance to live to breed. Circles: run 1's young males, the bigger the more of them.Right, from the preference strength: across, male colour; the mating probability when a female who likes bright meets him, darker higher. She keeps meeting males until one becomes her mate, so a male's share of the matings follows his mating probability. Circles: this generation's pairs.
Genes, traits, reproductionColour: two genes, each with a dull and a bright allele, add up to a male's colour (0, ¼, ½, ¾, 1). It shows in males; females carry the alleles and pass them on.Preference strength, onto colour → mating: how fast the mating probability falls as a male is duller than bright. Colour → mating follows it: dashed at 0.Cost of brightness, the red arrow: how much less likely the brightest male is to live (a male half bright pays half). Grey arrows: fixed.
Target500 birds on one island; every female likes bright. At the start 1 in 5 colour alleles is bright. Each colour allele turns into the other 1 time in 500 a generation. Go plays 100 generations, 16 times.The picture: what a hit looks like; the red box, where the thick line, the 16 runs' average, should end.
To finish
Hit the two targets. 0 of 2
Stage C is open.
R code
C
Finish Stage B to unlock this section.
Now what a female likes is a gene: a female with two liking-bright alleles favours bright males, one with none takes any male, one with one of each is in between. The liking does a female no good itself: her survival and her young are the same whoever she takes. See whether it spreads anyway, and what a cost to being choosy does to it.
Cost of choosiness, the red arrow from preference to reproduction, sets how much less likely a choosy female is to breed.
Fitness surfacesLeft, from the cost of brightness: a male's chance to live by his colour. Circles: run 1's young males.Right: the mating probability when they meet, male colour across, female preference up (takes any, in between, likes bright), darker higher. Circles: this generation's pairs.
Genes, traits, reproductionStage B's colour genes and mating; the preference is now a gene, with a liking-bright and a takes-any allele.Preference strength, onto colour → mating, is held at 6: for a female with two liking-bright alleles, half as strong for one.Cost of choosiness, the red arrow from preference to reproduction: how much less likely a female with two liking-bright alleles is to breed (half for one). Cost of brightness, held. Grey arrows: fixed.
Target500 birds on one island. At the start 1 in 5 colour alleles is bright, 3 in 10 preference alleles like bright. Go plays 100 generations, 16 times.The picture: what a hit looks like; the red box, where the thick line should end.
To finish
Hit the two targets. 0 of 2
Stage D is open.
R code
D
Finish Stage C to unlock this section.
Each bird now also carries harmful mutations, as in Lesson 16: each one cuts its chance to live, half of a parent's pass to each young bird, and every young bird gets a few new ones. Choosiness costs a female, as at the end of Stage C. See when the liking for bright pays its way.
How much they dull his colour, the red arrow from harmful mutations to colour. New harmful mutations a young bird gets, the arrow into harmful mutations.
Fitness surfacesLeft: a bird's chance to live by its harmful mutations (before the cost of brightness), each taking 5% off. Circles: run 1's young birds, the bigger the more of them.Middle, from how much they dull his colour: the colour a female sees on the brightest male, by his harmful mutations.Right: the mating probability, by the colour she sees. Circles: this generation's pairs, by his colour genes.
Genes, traits, reproductionStage C's genes and mating, the preference strength at 6, the cost of brightness and the cost of choosiness held.Harmful mutations: each takes 5% off a bird's chance to live (grey, fixed). The red arrow to colour: how much they dull the colour a female sees on a male.New harmful mutations a young bird gets: on average, on top of half of each parent's. Grey arrows: fixed.
Target500 birds on one island, carrying at the start about as many harmful mutations as the new ones each generation keep there. Go plays 100 generations, 16 times.The picture: what a hit looks like; the red box, where the thick line should end.
To finish
Hit the two targets. 0 of 2
Stage E is open.
R code
E
Finish Stage D to unlock this section.
Back to Stage B: every female likes bright, and brightness costs survival. Up to now the colour showed only in males. Here it can show in females too, where it costs them as it costs a male and wins them nothing. See what that does, and what a gene that switches colour off in females does.
Tick the box under the diagram to let the colour show in females. Cost of brightness, the red arrow, as in Stage B.
Fitness surfacesLeft, from the cost of brightness: the chance to live by colour, for a male (solid) and, when the colour shows in females, for a female in whom it all shows (dashed). Circles: run 1's young birds.Right: the mating probability when a female who likes bright meets a male, by his colour. Circles: this generation's pairs.
Genes, traits, reproductionStage B's colour genes, preference and mating; the preference strength held at 2.Colour genes → female colour: on when the box is ticked. The gene that switches colour off in females lands on that arrow.The cost of brightness acts on whoever shows the colour: the red arrow from male colour, and the one from female colour, which follows it. Grey arrows: fixed.
Target500 birds on one island; every female likes bright; at the start 1 in 5 colour alleles is bright, and where it is there, 1 in 10 alleles at the switching-off gene is the off allele. Go plays 100 generations, 16 times.The picture: what a hit looks like; the red box, where the thick line should end.
To finish
Hit the two targets. 0 of 2
That is the whole lesson.
R code
Good job!
That is all of Lesson 21. Your completion code is below — copy it and hand it in.