HUMAN REPRODUCTIONBIOLOGY 269

Today’s Humor:

We also think, and I’m sorry, gentlemen, if this disturbs any of your egos, that condoms should be marketed in three sizes, because the failures tend to occur at the extreme ends of the scale. In men who are petite, they fall off, and in men who are well endowed they burst. Women buy brassieres in A, B, and C cups and panty hose in different sizes, and I think if it would help condom efficacy, we should package them in different sizes and maybe label them like olives: jumbo, colossal, and super-colossal so than men don’t have to go in and ask for the small size.” Barbara Seaman, 1979 Testifying before the Senate Select Committee on Population

HUMAN REPRODUCTIONBIOLOGY 269

COURSE HOMEPAGE:

http://course1.winona.edu/ethompson/269.htm

The course syllabus is available online, linked to that homepage.

Let’s go over some specifics about the course.

Two things must happen in order for reproduction to be “successful”:

1. You must successfully pass your genetic information to your children.

2. Your children must survive long enough to reach productive age and pass that genetic information to their children.

Reproduction:

• Little energy required

• No mate needed

• Can be done anytime

• Requires more energy

• Mate must be found

• Mate must be ready

Asexual Sexual

So:If asexual reproduction is so much easier, why would any animal reproduce sexually?

Bacteria and other one-celled organisms reproduce asexually.

With only a couple of exceptions, all multicellular organisms reproduce sexually

Two Advantages to Sexual Reproduction:

• Offspring are genetically identical to parent

• Defective genes will all be expressed

• Adaptation very unlikely

• Offspring are genetic mixes of parents

• Defective genes can be masked by normal ones

• Adaptation possible

Asexual Sexual

1. Genetic

Two Advantages to Sexual Reproduction:

• Only one parent • Generally little or no care of

offspring possible

• Two parents available to care for offspring; one or both can devote more time/effort to raising offspring

Asexual Sexual

2. Care of Offspring

Sexual reproduction involves the formation of special reproductive

cells called gametes.

By definition, each gamete carries only half of the genetic information of the adult.

Combination: male+female gametes = FERTILIZATION

Offspring now carries same amount of genetic information as either parent

Fertilization may be external or internal

All but lowest organisms: male and female gametes.

Gametes are often unequal in both size and number.

Typically, the male produces large numbers of small gametes (sperm) while the female produces a much smaller number of large gametes (eggs)

Sexual reproduction requires two sexes which have different reproductive “strategies”.

As expected:Males and females have significantly different anatomyMales and females have significantly different physiologyMales and females have significantly different behavior

However: Both sexes have the same objective:To maximize their genetic contribution to subsequent generations

This involves:

• Maximizing number of fertilizations• Maximizing survival of embryos / fetuses• Maximizing birth survival of both mother and offspring• Maximizing survival of young offspring• Maximizing probability that offspring, when adult, will reproduce

Different species use different strategies:

• Some (e.g. fish) produce very large numbers of fertilizations and young from large numbers of both males and females

• Some (e.g. humans) produce small number of fertilizations and young from large numbers of both males and females

• Some (e.g. deer) produce small number of fertilizations and young from many females but a limited number of males

• Some (e.g. bees) produce a large number of fertilizations and young from a limited number of both males and females

Different species use different strategies:

• Some (e.g. fish) invest no energy in raising the offspring

• Some (e.g. birds, mammals) invest large amounts of energy in raising the offspring

Common feature:

Offspring which Are produced

Survive to adulthood

and Reproduce the next generation

should be the genetically “strongest” individuals

With that background in mind:

• Gather in groups of 4 - 6 individuals and discuss what reproductive strategies are important in humans, and how this affects our reproductive (sexual) behaviors.

• In about 5 minutes, each group will be asked to briefly present their conclusions

Sexual reproduction requires two sexes which have different reproductive “strategies”.

Typically in mammals:

Females invest large amounts of energy in:• Producing only a few eggs at a time

• Assuring their fertilization• Protecting the developing embryos• Protecting and nourishing young

Males invest large amounts of energy in:• Producing large numbers of sperm• Transferring sperm to female

Most mammals:

• Sexually active only certain times of year

• Females display physical signs when ovulating and sexually receptive

• Infants mature in relatively few years

• Short-term care of offspring

Humans:

• Sexually active at all times of year

• No physical changes in female when ovulating

• Long infancy and childhood

• Long-term care of offspring