Lecture Notes
LECTURE 1: THE EVOLUTION OF SEX
- Explain why the two sexes have evolved in most species
- Why, from an evolutionary point of view, this has been more successful than one sex as it leads
to recombination and variation of genetic material.
- Discuss which strategies are, evolutionary, the best for mating and reproduction.
CHAPTER 1 and 2
NATURAL SELECTION
- Some individuals are well suited to their environment
- Variation
- Heritability
- Reproductive differences
- Adaptations
Types of natural selection
- Survival selection
- Kin selection
- Sexual selection
o Intrasexual selection
▪ Direct competition for mates between members of the same sex, usually male-
male competition
o Intersexual selection
▪ Differences in attractiveness to the opposite sex, usually non-random mate
choice by females
Mechanisms Characters flavoured in the competing sex
Contests Size, strength, aggression, weapons, threat displays
Mate choice Behaviour and morphological traits to attract mates
Sperm competition Sperm displacement, high sperm production etc, harassment, punishment
coercion and forced copulation
- The Peacock's Tale… producing male hormones is expensive and costly and works better for
genetically fitter and healthier males. Showing off male hormones (as reflected in the tale, [or
mane, or muscle, etc., depending on species]) means showing off your male qualities.
- Females who pick males with these qualities benefit, as their offspring is genetically fitter and
healthier and more likely to survive.
- The Peacock's Tale… Unlike intrasexual selection, intersexual selection was considered a
scandal at Darwin’s times, as it meant that females have choice over whom they mate with.
, - But lets focus on intrasexual selection for now.
In most apes, males are larger than females because they have to compete with other males for access
to females who are willing to mate with them. Size and strength is a good indicator that a male is
dominant over other males.
Females have an interest in mating with other males, and a dominant male is trying to prevent this by
using strength and violence against females.
In humans, the apparent sex difference in size is much smaller than in most apes, however, this is
confounded by the distribution of body fats, which are more heavily layered in humans than other
apes. Once body fats are removed (e.g., by comparisons of skeletons) males are clearly much stronger
and larger than females.
,In humans, as in other apes, males compete for access to females, and they tend to threaten females if
they become interested in other
males.
The less time the couple has spent together (i.e., the greater the risk that the female has copulated
with another male),
the more sperm the male ejaculates
(even controlling for time since last ejaculation).
This suggests that intersexual selection (mate choice) is effective in humans (and other species).
- Baker and bellis 1993
THE PURPOSE OF SEX
- Sexual reproduction involves meiosis of genetic material with recombination within one
individual, then fusion with the others genetic material
ASSEXUALITY
- DNA replication and cell division
- Budding, shoots, and runners
- Self-fertilization
- Development of pre-fertilized eggs (parthenogenesis)
- Asexual individuals are female (grey). With sex, offspring is half female/half male. Males don’t
reproduce, hence the overall output is lower for sexual reproduction.
, BENEFITS OF SEX
Sex is time-consuming, expensive and dangerous so why do we bother?
Sex has benefits
- The BIG benefit of sex: Recombination provides a mechanism for genomic repair, eliminating
deleterious mutations (*).
- Parents can produce offspring that have higher fitness genotypes than themselves.
MULLER’S MUTATIONAL MELTDOWN IN ASEXUAL POPULATION
LECTURE 1: THE EVOLUTION OF SEX
- Explain why the two sexes have evolved in most species
- Why, from an evolutionary point of view, this has been more successful than one sex as it leads
to recombination and variation of genetic material.
- Discuss which strategies are, evolutionary, the best for mating and reproduction.
CHAPTER 1 and 2
NATURAL SELECTION
- Some individuals are well suited to their environment
- Variation
- Heritability
- Reproductive differences
- Adaptations
Types of natural selection
- Survival selection
- Kin selection
- Sexual selection
o Intrasexual selection
▪ Direct competition for mates between members of the same sex, usually male-
male competition
o Intersexual selection
▪ Differences in attractiveness to the opposite sex, usually non-random mate
choice by females
Mechanisms Characters flavoured in the competing sex
Contests Size, strength, aggression, weapons, threat displays
Mate choice Behaviour and morphological traits to attract mates
Sperm competition Sperm displacement, high sperm production etc, harassment, punishment
coercion and forced copulation
- The Peacock's Tale… producing male hormones is expensive and costly and works better for
genetically fitter and healthier males. Showing off male hormones (as reflected in the tale, [or
mane, or muscle, etc., depending on species]) means showing off your male qualities.
- Females who pick males with these qualities benefit, as their offspring is genetically fitter and
healthier and more likely to survive.
- The Peacock's Tale… Unlike intrasexual selection, intersexual selection was considered a
scandal at Darwin’s times, as it meant that females have choice over whom they mate with.
, - But lets focus on intrasexual selection for now.
In most apes, males are larger than females because they have to compete with other males for access
to females who are willing to mate with them. Size and strength is a good indicator that a male is
dominant over other males.
Females have an interest in mating with other males, and a dominant male is trying to prevent this by
using strength and violence against females.
In humans, the apparent sex difference in size is much smaller than in most apes, however, this is
confounded by the distribution of body fats, which are more heavily layered in humans than other
apes. Once body fats are removed (e.g., by comparisons of skeletons) males are clearly much stronger
and larger than females.
,In humans, as in other apes, males compete for access to females, and they tend to threaten females if
they become interested in other
males.
The less time the couple has spent together (i.e., the greater the risk that the female has copulated
with another male),
the more sperm the male ejaculates
(even controlling for time since last ejaculation).
This suggests that intersexual selection (mate choice) is effective in humans (and other species).
- Baker and bellis 1993
THE PURPOSE OF SEX
- Sexual reproduction involves meiosis of genetic material with recombination within one
individual, then fusion with the others genetic material
ASSEXUALITY
- DNA replication and cell division
- Budding, shoots, and runners
- Self-fertilization
- Development of pre-fertilized eggs (parthenogenesis)
- Asexual individuals are female (grey). With sex, offspring is half female/half male. Males don’t
reproduce, hence the overall output is lower for sexual reproduction.
, BENEFITS OF SEX
Sex is time-consuming, expensive and dangerous so why do we bother?
Sex has benefits
- The BIG benefit of sex: Recombination provides a mechanism for genomic repair, eliminating
deleterious mutations (*).
- Parents can produce offspring that have higher fitness genotypes than themselves.
MULLER’S MUTATIONAL MELTDOWN IN ASEXUAL POPULATION
