HDE 117 Lecture 6: HDE117 - L6

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University of California - Davis
Human Development
HDE 117
James Carey

Lecture 6 I. Life Span Concepts A. Life Span: Conceptual Issues 1. Life duration – broader concept than life span 2. Individual – discrete functional entity 3. Genesis – conception; fetal stage; birth; adulthood 4. State of Existence – normal; arrested metabolism 5. Time of Existence – normal plus period of arrest 6. Extinction – death; fission; fusion B. The Life Span Concept: Examples Where the Lines are Blurred 1. Amoeba forming ‘macro’ organism 2. Hydra replacing all of cells every 10 days 3. Flatworm split into separate parts 4. Embryos dividing to form clones (e.g. identical twins) 5. Chimeras formed when embryos fuse 6. MAIN POINT: issues concerning level of individualism birth and death processes, and the disappearance of original individuals invalidate the classical definition of life span for many organisms and/or for certain situations with humans C. Quantum Nature of Death 1. Progression: a. Coma i. Breath stoppage  Heart stoppage - Brain death  Cessation of growth/metabolism + Tissue degradation ~ Loss of DNA integrity 2. How can a person be deader than dead? a. Death of immediate family members, extended family members, whole clan, whole ‘race’, all humans, all of life 3. Related Concepts a. Mortal – destined to die b. Immortal – living forever c. Eternal – life after death d. Infinity – endlessness e. Determinate – fixed growth or age f. Indeterminate – open-ended growth or life span 4. Life Span and Age a. Two types of Ages: i. Chronological  Postnatal age – from birth  Total age – from conception ii. Physiological 5. Tree of Life a. Crown group – last is the smallest monophyletic group, or “clade”, to contain the last common ancestor of all extant members, and all of that ancestor's descendants II. Biodemography A. Biodemography: Vertebrate Life Spans 1. Species that are large, social, armored, and subterranean live longer a. Armored (turtles, armadillos) b. Subterranean (mole rats, ant queens) 2. Birds live longer than similar-sized mammals a. Birds live relatively long years; very long-lived relative to their size 3. Primates long lived mammals and humans are long-lived primates a. Humans are even more long-lived than primates 4. Relationship between size and longevity not hold within orders nor between some orders such as bats vs rodents a. Bats: small, live very long time; b. Dogs: small breeds live a long time c. Dogs: big breeds don’t live so long (reverse relationship between size and longevity) d. Ponies live longer than horses 5. Extreme long-lived species in all groups a. Elephants (80 years) b. Whale (96 years) i. *Bow-head whale lives up to 250 years – why are they able to? c. Insects, rodents – short lived BUT bats (insectivores) are tiny and live so long d. Fish: can live very long life spans B. Biodemography: Insects 1. Summary a. Over 5,000-fold difference in insect life spans b. Beetles, social insect queens, primitive spiders, and ticks are all long-lived c. Large variation both within and between orders C. *Allometry of Lifespan [slide 49-50] b 1. Allometry of Lifespan – L = aX a. L = lifespan ~ X = an attribute (e.g. body mass) ~ ‘a’ = baseline rate ~ ‘b’ = allometric scal
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