HUMAN REPRODUCTION BIOLOGY 269

HUMAN REPRODUCTION BIOLOGY 269 COURSE HOMEPAGE: http://course1.winona.edu/ethompson/269.htm The course syllabus is available online, linked to that homepage.

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.

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.

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

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

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

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)

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

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

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)

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

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

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

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

Common feature: Offspring which are produced: and 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. 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

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