Introduction to human biology -- life and evolution

I.  Introduction

- human biology involves more than study of body (see course goals)

• relationships with society
• relationship with environment

II.  Characteristics of life

A.  Life is diverse

-  we share the planet with 30 million or more species

• three major groups, domains:
  • Bacteria -- prokaryotes
  • Archaea -- prokaryotes
  • Eukarya -- eukaryotes
    • plants
    • animals
    • fungi
    • protozoans

-  diversity is a result of evolutionary processes that have been occurring since life originated on planet more than a billion years ago

• different habitats = different species

- evolution results in increasing complexity of species -- driven by accumulation and storage of genetic information

B.  Life is variable

-  within species there is variation from individual to individual

• result from sexual reproduction
• result from mutation

- variations allow species to adapt and evolve

C.  Life is organized

-  "Life is nothing more, nothing less, than the structural organization of certain molecules", Boyce Rensberger, Science 80.

• dehydration experiments with brine shrimp, yeast
• cryopreservation of cells
• in both cases cells instate of suspended animation

-  living organisms exhibit a high degree of organization of structure and function

-  matter in universe can be organized hierarchically: atom, molecules, organelle, cell, tissue, organisms, organ systems (in multicellular organisms), organism, population, community, ecosystem, biosphere

• each level must "obey" laws of levels below it
• each level has unique properties that emerge from interaction at the lower levels -- emergent properties that cannot be predicted based on what we know about lower levels

-  where on hierarchy does life begin?

• molecules?
• organelles?

-  life is cellular -- cell theory

• cells are structural and functional units of all living things
• activities of an organism are dependent on individual/collective activities of all cell
• activities of cells made possible by subcellular structures
• continuity of life has a cellular basis

-  are viruses alive?

-  is the earth alive?

D. Life can move

-  life shows movement at all levels of organization -  atomic, molecular organismal

E.  Life is self regulating

-  homeostasis -- ability of living things to maintain ever changing internal conditions within a narrow tolerable range

-  examples of homeostasis

F.  Life is chemically unique

-  organic compounds contains carbon

-  99% of all elements in living things are carbon, hydrogen, nitrogen, oxygen

- organic molecules -  "life is polymeric"

G.  Life is based on water

-  75% - 95% of most organisms made up of water

H.  Life can reproduce

-  reproduction at cellular level - mitosis, meiosis

-  reproduction at organismal level -- sexual or asexual means (clones)

I.  Life has a plan

-  organisms contain genetic instructions -- DNA

-  these instructions transmitted from parent to offspring

J.  Life grows

-  both in size, cell number

K.  Life adapts and evolves -- life has a history

-  lifeless earth --> chemical evolution (development of organic chemicals) --> life (prokaryotic) --> biological evolution (photosynthesis --> eukaryotic organisms --> multicellular organisms)

1.  Evolution

-  process by which one species gives rise to another

• evolution is the process by which a species becomes adapted to its environment
• concept of common ancestry for all species
• explains both diversity and fact that many species share common features

-  Charles Darwin

• evolution by way of natural selection
• drew on ideas of Rev. Thomas Malthus, 18th. century theologian/economist
  • populations increase exponentially, resources increase arithmetically
  • populations grow faster and eventually use up resources
  • leads to competition for resources
• natural selection -- those individuals with traits that are most successful will increase in frequency over time
  • are better adapted
• example of natural selection -- peppered moths, England
  • dark colored or gray speckled
  • fly at night, on trees during day
  • trees had lichens until mid 1800's
    • gray speckled more common
  • from 1848 - 1898 dark colored variant increases in frequency
    • industrial revolution
• thus adaptation is end product of evolution

L.  Life metabolizes

-  capacity to obtain and convert energy from surroundings

-  capacity to use energy in the maintenance and growth

L.  Life dies

-  Levine and Miller, 1994, "death is equilibrium with the environment"

M.  Life interacts with environment

1.  irritability

2.  ecology

III.  The interdependency of life

A.  Autotrophs and heterotrophs

• autotrophs -- plants and other photosynthetic organisms
  • capture energy of sunlight and convert it to forms they can use to build organic compounds
• heterotrophs -- depend directly or indirectly on energy stored in tissues of producers

B.  Relationships between autotrophs, heterotrophs, abiotic environment

1.  One way energy flow through ecosystems

• second law of thermodynamics -- when energy converted from one form to another, some of the energy becomes unavailable to do work
  • no physical or chemical reaction is 100% efficient
  • " not all the energy can be used as it is converted from one form to another"

2.  Nutrient flow through ecosystems

• recycling
• role of decomposers
• implication with pollutants, toxins

IV.  The scientific method, a case study