1. Sexual Selection -
The Dating Game!

2. Sexual selection New species arise through natural selection.
The individuals that survive and reproduce are those with characteristics that give them an advantage over others.
One kind of natural selection is sexual selection.
There are two main types of sexual selection – mate choice and competition for mates.
Extra information
The theory of sexual selection was originally posed by Darwin, although significantly more theory has been added since e.g. cryptic female choice.
Scarlet macaw

3. Male Indian peafowl displaying
Mate choice
In some species, females choose males to mate with - this is known as intersexual selection.
Females prefer males with better “ornaments”.
Males have evolved bigger and better ornaments.
Examples of ornaments include bright colouration and extravagant plumage.
Ornament definition: A is a structure of an animal that appears to serve a decorative function rather than a practical function. Ornaments are used in displays to attract mates.
Extra information
“Good genes” vs “sexy son” theory.
Good genes theory: females choose males with large/conspicuous ornaments as it means that they have strong genes that enable them to survive with this handicap e.g. can still escape from predators, have a strong immune system. These genes would then be passed on to their offspring which would increase their evolutionary fitness.
Sexy son theory: females choose males with large/conspicuous ornaments as it means that their sons will inherit the genes for these ornaments and will be preferred by females in the next generation, increasing their evolutionary fitness.
Related ARKive video - Indian peacock displaying to females:
Male Indian peafowl displaying

4. Male Nubian ibex with large horns
Competition for mates
In some species, males fight other males for females. This is known as intrasexual selection.
Males have evolved secondary sexual characteristics also known as weapons.
Examples of weapons include horns and antlers used for fighting.
Males with bigger and better weapons ‘win’ more females so weapons have evolved to become bigger and better over time.
Extra information
Males with genes for effective weapons are more successful in mating with females, producing more offspring with the same ‘strong’ genes. Therefore future populations have a higher proportion of males with more effective weapons.
Related ARKive video – Nubian ibex males fighting:
Male Nubian ibex with large horns

5. How does sexual selection work?
The Dating Game!
How does sexual selection work?

6. Greater bird of paradise
Male greater birds of paradise have ornaments in the form of elaborate plumage to attract females. This is an example of intersexual selection.
Play the greater bird of paradise dating game to show how female birds of paradise choose their partners.
Female
Male

7. Reindeer
Reindeer bulls fight for females during the rut using their antlers – a form of secondary sexual characteristic. This is an example of intrasexual selection.
Play the reindeer dating game to show how males compete for females.

8. The Dating Game!
Through both competition for mates and mate choice, species evolve ornaments or weapons to attract or fight for mates.
The genes responsible for these characteristics are then passed on to the next generation.
Ornaments therefore get larger and more effective over time, following female preference.
Weapons get larger and more effective over time as males with the ‘best’ weapons ‘win’ more mates.

9. Discussion
Are the complex calls of songbirds due to mate choice or mate competition?
What limits the size / visibility of ornaments and weapons?
This is probably more a result of mate choice – even though males may compete, females will only approach males with songs they find attractive.
Size and visibility of ornaments are probably limited by the handicap they entail – for example large or complex ornaments take considerable effort to maintain (e.g. physical resources) and also might make them more vulnerable to predation. Bright and visible colouration may also increase visibility to predators.