Life and Death. A Biologist Looks at the Living State of Matter.

• Death in populations.

• Programmed cell death.

• Death by cancer.

• Death of the embryo/fetus (abortion).

Why Death is Inevitable

• If organisms lived forever, they could not, given finite resources, have offspring.

• Without reproduction, evolution could not occur since there would be no new varieties from which to select.

• If there were no evolution, species could not adapt to changing environments and would die.

• If organisms lived forever, they would die.

R-selected species

• have high reproductive rates• occur in unpredictable environments• have a type III survivorship curve

K-selected species

• have low reproductive rates• occur in stable environments• have a type I survivorship curve

r = growth rate

K = carrying capacity

Prehistoric humans at the time of their emergence as a new species.

The demographic transitionr K

Take Home Lesson

• As human populations approach the carrying capacity of the planet, the human species adopts an increasingly K strategy.

• Birth and death rates are less frequent when K is reached.

• This makes individual life more meaningful and death more unacceptable.

Death at the Cellular Level

• First instar larva: 558 cells• Four molts: 959 cells in fourth instar• 131 cells die by apoptosis

350 cells of developing first instar shown in this diagram

Take Home Lesson

• Cells possess “death programs” hard-wired into their genes.

• Cell death is a necessary part of embryonic development.

• Once again, death is necessary for life.

A cirrhotic liver containing a malignant neoplasm (a hepatocellular carcinoma):

                                                            

Metastases in liverMultiple metastatic tumors in the liver

The Hayflick Limit

Cancer cells are immortal!!

Henrietta Lacks (1920-1951?)

HeLa cells in culture (2006)

Question

• Is Henrietta Lacks really dead?

http://www.youtube.com/watch?v=eOz0Q_0yOtU&feature=related

http://www.youtube.com/watch?v=0gF8bCE4wqA

radiolab

Take Home Lessons

• Only cancer cells and germ cells are immortal.

• Most of what we consider self is mortal (programmed to die).

• In a real sense, you will be immortal through your children; you are your parents’ immortality.

And if men strive together, and hurt a woman with a child, so that her fruit depart, and yet no harm follow, he shall be surely fined, according as the woman's husband shall lay upon him; and he shall pay as the judges determine. But if any harm follow, then shalt thou give life for life... (Exodus 21: 22)

Questions to help us think more clearly...

• When does life begin?

• When does human life begin?

• When does individual human life begin?

• When does personhood begin?

When does life begin?

• Cellular life evolved on the planet earth approximately 4.5 billion years ago.

• .

Primordial Alliance, Juan Miguel Giralt

When does human life begin?• Homo sapiens is a 200,000 year old species.

When does individual human life begin?

• The genes that are unique to an individual are first present in a common cell after fertilization.

• BUT the expression of these genes may not be detected for several days.

• BUT twinning can occur as late as 9 days after fertilization.

When does personhood begin?

• Section 1. All persons born or naturalized in the United States, and subject to the jurisdiction thereof, are citizens of the United States and of the state wherein they reside. No state shall make or enforce any law which shall abridge the privileges or immunities of citizens of the United States; nor shall any state deprive All persons born or naturalized in the United States, and subject to the jurisdiction thereof, are citizens of the United States and of the State wherein they reside. (14th Amendment to the United States Constitution)

Three positions on abortion

• A human being comes into existence at the moment of fertilization. Abortion after this point is murder.

• Abortion of an embryo at any time prior to viability (end of second trimester) is morally-neutral.

• The longer an embryo/fetus develops, the more objectionable is an abortion.

Take Home Lessons

• Aborted embryos are living organisms.

• Life develops.

• There is a distinction between embryos and fetuses. Is it a meaningful difference?

• If so, legal abortion reduces the mean age of aborted embryos/fetuses.