1. HUMAN REPRODUCTION BIOLOGY 269

2. HUMAN REPRODUCTION BIOLOGY 269
COURSE HOMEPAGE:
The course syllabus is available online,
linked to that homepage.

3. Biologists like to talk about biological imperatives - the things which living organisms, including humans, need to do continue the survival of themselves and their species.
These include such things as
- establishing a territory within which they can survive
- adapting to their environment
- finding and consuming food and water
- protecting themselves from predation
At the top of the list, however, is reproduction.
This is something which all species must do.

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

5. Reproduction: Asexual Sexual Little energy required
No mate needed
Can be done anytime
Requires more energy
Mate must be found
Mate must be ready
Bacteria and other one-celled organisms reproduce asexually, as can some higher-level species.
With only a couple of exceptions, all multicellular organisms can, and usually do, reproduce sexually

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

8. Two Advantages to Sexual Reproduction: 1. Genetic
Asexual
Sexual
Offspring are genetic mixes of parents
Defective genes can be masked by normal ones
Adaptation possible
Offspring are genetically identical to parent
Defective genes will all be expressed
Adaptation very unlikely

9. Two Advantages to Sexual Reproduction:
2. Care of Offspring
Asexual
Sexual
Only one parent available, and usually provides no care to the offspring to help them survive.
Two parents available to care for offspring; one or both can devote more time/effort to raising offspring
(although this does not always happen)

10. All sexually reproducing species have evolved reproductive strategies which improve the chances of successful reproduction:
Passing genetic information
to the next generation
Ensuring that offspring survive
to do the same thing

11. Sexual reproduction involves the formation of special reproductive cells called gametes.
All but lowest organisms: male and female gametes.
Each gamete carries only half of the genetic information of the adult.
Combination: male+female gametes
= FERTILIZATION
Fertilization may be external or internal
Offspring now carries same amount of
genetic information as either parent
BUT it is not identical to that of either
parent

12. Gametes are often unequal in both size and number
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)

13. Sexual reproduction requires two sexes which have different reproductive “strategies”.
As expected:
Males and females have significantly different anatomy
Males and females have significantly different physiology
Males and females have significantly different behavior
However: Both sexes have the same objective:
To maximize their genetic contribution to subsequent generations

14. Reproductive Biologists often group reproductive strategies into two types
R- strategies: Rapid reproduction, many offspring, little parental care, lower survival of offspring. Usually small body size, rapid sexual maturation, short lifespan
K-strategies: Slow reproduction, few offspring, more parental care, higher survival of offspring. Usually large body size, slow sexual maturation, longer lifespan

15. Some species are monogamous
Some species are polygamous
Polygyny: one male, many females
Polyandry: one female, many males
Some species are promiscuous

16. Most mammals: Humans: 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

17. Common feature: Offspring which are produced:
and survive to adulthood,
and reproduce the next generation
should be the genetically “strongest” individuals

18. With that background in mind:
Gather in groups of individuals and discuss what reproductive strategies are important in humans, and how this affects our reproductive (sexual) behaviors.
Those behaviors may be (and in fact definitely are) different for men and women. Think about such things as numbers of gametes, sexual behavior, parenting tasks, etc.
In about 5 minutes, each group will be asked to briefly present their conclusions

19. Here’s the bottom line: Almost everything about human sexuality and sexual behavior are part of our reproductive strategies, which have evolved over millions of years:
Anatomy
Finding partners for sex
Finding partners for parenting
Female receptivity
Sexual desire
Sexual arousal
Sexual pleasure
Ovulation patterns
Sexual intercourse
Internal fertilization
Monogamy/Polygamy/Promiscuity
Small number of offspring
High survival of offspring