BIOL 103 Biology in SF Syllabus
BIOL 103 Biology in Science Fiction
Study Guide

Reproduction of Living Organisms
The Universe, where Life Began
Evolution: How kinds of life endure and change
The Biosphere
Mars—Almost a Biosphere
Energetics in Ecology
Material Cycles in Ecology
Population Interactions
Genetic Inheritance
Molecular Genetics
Development of an Organism
Chromosomes, Speciation, and Artificial Selection
Reproduction of Living Organisms    >>Top>>
    3. In nature, exponential growth can never continue indefinitely. Growth is slowed by: depletion of essential resources; buildup of toxic wastes or poisons; predation or disease.

     4. Decrease of a population (due to the factors listed in point 3) usually occurs exponentially. The rate of decrease may be faster or slower than the previous rate of increase.
     
      5. In nature, most populations grow at a rate balanced by death due to disease, waste buildup, resource limitation etc. There are cycles of growth and decline.

      6.  Reproductive success is increased by dispersal of organisms, or of their gametes (sperm or eggs).  Dispersal can be by environmental elements (wind or water); by the organism’s own motility; or by another organism (a “carrier” or “vector”).  Dispersal by a vector can be parasitic (harmful) or mutualistic (mutually beneficial).

The Universe, where Life Began   >>Top>> 1. Time is a fourth dimension of space, in which we can only travel forward.
  2. Structural order decreases over time. Disorder, "entropy," increases. But order, or complexity, can increase locally, if elsewhere order decreases more.
  3. Energy absorption can drive local increases in complexity, such as growth of living organisms.
  4. The ultimate source of all energy used by life on Earth comes from the Sun, where hydrogen nuclei fuse to form helium.
  5. The energy released by nuclear fusion radiates out from the Sun, at wavelengths all across the electromagnetic spectrum: radio, microwave, visible light, ultraviolet, gamma rays.
  6. When energy radiated by the Sun reaches Earth, all wavelengths may be absorbed; but only visible light is captured efficiently by producer organisms such as green plants and bacteria. Light energy drives most living ecosystems. Some deep-sea and deep-earth ecosystems are driven by chemical reactions without direct input of light.
  7. All energy used by living organisms ends up radiated away as heat radiation (infrared) which is low order, high entropy. Thus, despite apparent increase of complexity as organisms grow, entropy increases overall.
   8. In older stars, hydrogen gets used up, and helium fuses to produce heavier nuclei. The commonest stellar reactions form the atoms most common in our living bodies: hydrogen, carbon, nitrogen, and oxygen.
   9. How did heavier elements get into our solar system, if our Sun is too young to have formed them? Heavier elements on Earth are the dust of older stars that died explosively as supernovas. Evolution: How kinds of life endure and change   >>Top>> 1. Living organisms produce offspring that look similar to their parents; but also slightly different.  
2. Over time, these small differences accumulate at random. Smaller populations accumulate change more rapidly than large populations. If some individuals leave slightly more offspring than others, their traits will increase in frequency in succeeding generations.
  3. When a population becomes very small (a population bottleneck), the chance is high that it will either go extinct, or evolve into a different species.
   4. If two populations of the same species are separated (prevented from interbreeding) they eventually will evolve different frequencies of traits. If separate long enough, they may become different species, incapable of interbreeding.
  5. Organisms may be classified based on genetic relatedness, or the time since two species diverged from a common ancestor. This is different from ecological classification (discussed later, with Dune and A Door into Ocean).
  6. When environmental conditions favor production of offspring by individuals with certain inherited traits over individuals with different inherited traits, this is called natural selection.
  7. Changes in inherited traits are called mutations. Mutations diminishing function are more common than mutations improving function. Therefore, in the absence of natural selection favoring a trait, the trait usually deteriorates over many generations, because random mutations accumulate and are not selected against.
   8. Traits that confer advantage in natural selection always confer disadvantage as well. If advantage outweighs disadvantage, then the trait will increase in future generations. 9. Selection favors traits that enable type A to leave more survivors than type B, even if both types nearly go extinct.
  10. Environments change, either from external causes, or because the organism changes its own environment.
  11. When the environment changes, previously selected traits become deleterious. Many species go extinct. Other species increase in prominence, as the new conditions favor their traits. But in the short term, more species are lost than gained, and diversity decreases.
  12. Environmental stability favors evolution of many diverse species occupying specialized niches. Diversity increases.
   13. When environmental changes occurs in predictable cycles, organisms may evolve regulatory switches that enable them to survive the changed conditions. But many cycles of change are required for this evolution to occur.
   14. As species diverge through evolution, one species may occupy a niche that an unrelated organism occupies in a distant location. The two species may evolve superficially similar adaptations; hence the term convergent evolution. But despite the apparent similarity, the two species never merge or interbreed.
  15. Reproduction occurs by passing on genes which are the "blueprint" for inherited traits. If an organism "survives" without passing on traits, its survival "doesn’t count" in evolution.
   16. Organisms can actually pass on their traits without producing their own offspring—if they assist reproduction of a relative who shares their genes.   This is known as kin selection.
  The Biosphere   >>Top>> 1. Life on earth may be considered on various levels of scale. Individual organisms form populations of particular species. Populations of different species participate in ecosystems. All ecosystems are linked within the planetary biosphere.
  2. For life to exist in a biosphere, a planet needs sufficient gravity to hold essential gases in its atmosphere, such as oxygen (O2), water (H2O), and nitrogen (N2).
  3. The average temperature and atmospheric pressure must be high enough (but not too high) to permit existence of liquid water.
  4. The oxygen chemistry of the upper atmosphere must generate enough ozone (O3) to protect the planet’s surface from ultraviolet radiation (UV). UV radiation breaks the bonds between atoms of biological molecules, especially DNA.
   5. The initial outgassing (release of gases by volcanoes) of an Earth-sized planet produces an atmosphere composed mainly of carbon dioxide (CO2).
  6. Photosynthesis by microbes (and later by plants) produced all the oxygen in Earth’s atmosphere, and fixed most of the carbon dioxide as complex organic components of living organisms.

7. Denitrification of nitrate (NO3-) by microbes produced most of the N2 in the atmosphere. N2 is "fixed" by microbes which build nitrogenous organic compounds, such as amino acids for proteins. All living organisms depend on microbes to fix nitrogen.

 Mars—Almost a Biosphere   >>Top>> 1. The temperature of the Martian surface and atmosphere varies from cold to colder; always below the freezing point of water, and usually below freezing for carbon dioxide.
  2. The Martian atmosphere is less than 0.5% as dense as that of Earth. At this pressure, liquid water cannot exist; from ice, water vapor sublimes into the atmosphere. But water has flowed in the past, when conditions must have been different from now.
  3. The atmosphere is mostly carbon dioxide. It is nearly saturated with water vapor, but the total water content is low, because the overall density of gases is low. Most oxygen is bound in iron oxides in the regolith. Virtually no O2 is in the atmosphere.
  4. Most of the water on Mars was outgassed by volcanoes. Now much of the water is frozen in the northern ice cap, and within the regolith (Martian soil). Carbon dioxide ice is frozen in the southern ice cap, and in the regolith.
  5. How do we know all this? The Mariner spacecraft used UV spectroscopy, measurement of UV absorption by the atmosphere. The Viking landers used mass spectroscopy to analyze molecules in the atmosphere; and they sampled the regolith.
  6. The Viking landers found no evidence of living organisms, based on experiments designed to detect things Aeating" radiolabled carbon "foods," or photosynthesizing radiolabeled carbon dioxide.
  7. NASA scientists found that a Martian meteorite contained (1) minerals typically produced by microbes; (2) microscopic structures resembling fossil bacteria. They hypothesize that microbes may be living deep within Martian crust, similar to rock-eating microbes on Earth. Energetics in Ecology   >>Top>> 1. Overall, energy cannot be created or destroyed. Energy can be transformed among different forms: electromagnetic radiation, chemical bonds, mechanical movement. (Nuclear reactions can transform mass into energy; this happens only within stars and within nuclear reactors, NOT within pre-human ecosystems.)
  2. As energy is transformed, a certain portion always escapes as heat, and therefore unavailable for any future living organism. Thus, energy cannot be recycled. Energy does pass between organisms along the food chain, but ultimately all energy is lost as heat radiated off the planet.
  3. Primary producers build CO2 into complex biological molecules. They require a constant supply of (1) light energy for photosynthesis (most ecosystems) or (2) reduced minerals for lithotrophy, upwelling from volcanoes (small ecosystems, very limited contribution to biosphere.)
  4. Consumers eat producers or other consumers, using respiration (combining with oxygen, or oxidized minerals) or fermentation (food breakdown without oxidation).
  5. Natural selection favors survival of those organisms who use energy most efficiently, dissipating the least waste heat while producing the most offspring. For example, photosynthesis and respiration both are processes that transform 95% of the chemical energy theoretically available for cellular processes.
  6. Despite strong selection for efficiency, about 90% of available energy is lost by every consumer up the food chain. That is why eating meat is more "expensive" ecologically than eating vegetables.
  7. Because producers and consumers evolve simultaneously (coevolution) it turns out that consumers can actually have beneficial effects on the producers they consume; not "on purpose," but because the producer adapts to an environment that includes the consumer. Material Cycles in Ecology   >>Top>> 1. Water is an essential part of every ecosystem. All habitats, from ocean to desert, include some water that evaporates into the atmosphere, driven by solar energy (heat). Evaporation of water is the first part of the hydrological cycle. 2. When changes in atmospheric temperature and pressure decrease its physical ability to hold water, the water vapor condenses as clouds, which ultimately precipitate as rain. On the oceans, more water evaporates than falls as rain. On dry land, the reverse is true. Rainwater returns to the ocean through rivers and wetlands, an exceptionally productive habitat for life. 3. One source of rainfall is that air currents reach mountains and rise, cooling, so that the water condenses, forming clouds and rain. As the air current continues across the mountain, it is dry and tends to dry out the land below; this region is likely to be a desert. Deserts can also exist in regions where winds from the equator descend, warming and picking up moisture (about 30o north and south of the equator.) 4. Below land, water exists in underground lakes called aquifers. Many aquifers in the United States are being pumped out by humans faster than rain refills them. Water from aquifers always contains trace salts; these tend to build up during irrigation of crop lands (salinization). Aquifers can be contaminated permanently by industrial or agricultural pollution. 5. Carbon cycles between CO2 in the atmosphere, the body parts of plants and animals, and carbonates in the oceans. Human industrial pollution has produced more CO2 than plants can assimilate, resulting in increased retention of heat by our atmosphere; this is called the greenhouse effect. (For comparison, see oxygen & nitrogen cycles, p. 5.)

6. Decomposers are needed to decrease buildup of dead plant and animal bodies and recycle their minerals in the ecosystem. In some ecosystems, fire plays the role of decomposer.

 Population Interactions   >>Top>> 1. A species evolves to fill a certain niche in the ecosystem. The niche is defined by habitat, choice of food, and other environmental needs. Usually two species in an ecosystem cannot occupy exactly the same niche, although they may compete for aspects of it. 2. If one species of organism exists, chances are that related species exist in the ecosystem. The species must have evolved to occupy slightly (or extremely) different niches. 3. Other species in the ecosystem (not related genetically) form part of the habitat of any given species. Change in the population size of Species A may cause change in the population size of Species B. A "ripple" effect can occur throughout the ecosystem, with results hard to predict. 4. About 90% of available energy is lost by every consumer up the food chain. That is why eating meat is more "expensive" ecologically than eating vegetables. In any ecosystem, the "biomass" of organisms will be lower on the higher (consumer) levels of the food chain. 5. Because producers and consumers evolve simultaneously (coevolution) it turns out that consumers can actually have beneficial effects on the producers they consume; not "on purpose," but simply because the producer has adapted to an environment that includes the consumer.

6. Parasitism is an interaction between two species in which Species A (parasite) benefits at the expense of Species B (host) without immediately killing the host. The host may die eventually as a result of negative effects.

 7. A commensal enjoys benefits from a host, while neither harming nor benefiting the host. Commensals are usually more common than parasites, and possibly more highly evolved, because they best maintain a high-quality habitat (a healthy host.) 8. Cooperation may occur between two species who provide things for each other that neither could obtain as effectively on its own. Some species may cooperate or cheat, depending on the environmental conditions. 9. A highly intimate, necessary association between two species is called mutualism or symbiosis. When one partner actually lives inside the other, this is called endosymbiosis. 10. Within a species, individuals may cooperate as a group in order to compete successfully against other groups, if the net result is increased reproduction of genes for all group members. 11. Individuals always share some degree of genetic inheritance. Two siblings inherit 50% of the same genes. Two cousins inherit 25% of the same genes. 12. Altruism occurs only when an organism can increase propagation of its own genes by sacrificing itself or its resources for another organism. (This is still a controversial theory, especially its application to humans.) 13. Some individuals reproduce their genes by helping relatives instead of (or in addition to) producing their own offspring. This is known as kin selection. How organisms "know" who their relatives are is a fascinating question in behavioral biology. 14. Kin selection may operate among humans; this question is studied by anthropologists. Some scientists believe that "cultural evolution" takes precedence over genetic evolution; that human behaviors tend to propagate reproduction of cultural processes and beliefs, rather than (or in addition to) propagating genes. Genetic Inheritance    >>Top>> 1. The chromosomes contain the genetic blueprint for the organism to develop and function. Bacteria have one circular chromosome. Plants and animals have several linear chromosomes in the nucleus of each cell. Most multicellular organisms have two copies of each chromosome, one from the mother and one from the father.

2. Sex determination occurs differently in different species. In humans, two X chromosomes makes a female; XY makes a male. The Y chromosome actually has degenerated through evolution, and now carries very few genes. Thus for males, most of the genes on the X chromosome (for example, red/green color vision) are inherited only from the mother. In bees and ants, male arise from non-fertilized eggs, inheriting all genes from the mother.

3. Chromosomes consist of DNA, a linear double helix that encodes information in a four-letter "alphabet." The sequence of information in the DNA constitutes genes. Each gene specifies one functional product.

4. DNA information can be copied into RNA, a disposable copy of the "permanent" information in DNA. Some RNA molecules perform tasks of their own in the cell. But most RNA molecules are messenger RNA, each of which directs ribosomes to make a particular protein.

5. Each protein, determined by a particular gene, has a particular function in the cell; for instance hemoglobin carries oxygen.

6. The two different copies of a gene provided by the two different parents can differ slightly in information. These slight differences arise rarely, from mutation of the DNA sequence; but once they occur, they are inherited indefinitely by Mendelian rules.

7. If the two parental copies of a gene differ in function, the function of one copy may mask the function of another. The copy whose function is expressed is said to be dominant. The masked copy is recessive. Often a recessive gene is simply a non-functional copy.

 8. In "real life," expression of genes is very complicated, depending on: regulation by factors of the environment; developmental stage; interaction with other genes; and chance.

9. Some naturally occuring viruses contain DNA that can be spliced into the chromosome of a host cell, by enzymes that the virus encodes and expresses. A plasmid is a circular loop of DNA that needs a host cell to replicate (like viruses) but does not destroy the host. Some plasmids can splice DNA into a host chromosome.

10. In the laboratory, we can create an artificial splicing reaction using enzymes purified from bacteria, and DNA purified from any source. Pieces of DNA from anywhere, including a human, can be spliced into a plasmid or a viral chromosome. This is popularly called "recombinant DNA."

11. DNA spliced into a vector (plasmid or viral chromosome) can be put into a host cell, where it replicates and is expressed as part of the host. This is called genetic engineering.

12. Genetic engineering can be used to construct bacteria that will make a valuable product, such as human growth hormone or insulin. The protein product is then applied as a medical therapy.

13. Genetic engineering can be used to splice a DNA gene directly into a chromosome of a host, such as in human body cells. A functional gene copy may replace a non-functional copy, curing a defect. This is somatic gene surgery or gene therapy.

14. If a gene were to be spliced directly into the sex cells of a host, and "cure" the defect in the eggs or sperm, the transmission of the "defective" gene to future generations would be prevented. This is called germ-line gene surgery.

 Molecular Genetics           >>Top>> 1. The nucleotide bases are: Adenine, Thymine, Cytosine, and Guanine. All genetic information is encoded in pairs of complementary nucleotide bases: A-T, T-A, C-G, G-C. The ladder of base pairs is twisted into a helix. The DNA molecule replicates itself by "unzipping"down the middle, while each strand progressively fills in its new complementary strand. This process is performed by polymerase enzymes.

2. The replication of DNA is extraordinarily accurate; less than one mistake in a billion base pairs. But over a large number of base pairs, and many generations, errors (mutations) are bound to occur. Mutations are increased by mutagens, such as oxidative reactions or ultraviolet light absorption.

3. On average, the mutation rate for most species is constant over time. Therefore, one can measure the time of evolution by counting the number of base-pair differences between the genes of two species. These data tell us, for example, that humans diverged from gorillas more recently than we diverged from organgutans. If we had enough dinosaur DNA, we could tell whether in fact dinosaurs diverged from birds more recently than from reptiles.

4. We can purify DNA from unknown samples, and a polymerase enzyme from a standard source (a thermophilic bacterium is used, whose polymerase can withstand boiling temperature). The polymerase can perform cycles of unzipping DNA and replicating it. This process is called polymerase chain reaction (PCR). It can amplify tiny traces of DNA a million-fold.

5. The pieces of amplified DNA are very short (100-1,000 base pairs). A vertebrate chromosome may contain billions of base pairs. Thus, to reconstruct an entire chromosome of an extinct organism would require "piecing together" many short overlapping sequences.

6. Genes and chromosomes evolved along with the organisms in which they reside. Many genes have duplicated themselves within the organism; then the duplicates evolved into distinct functions. Members of these gene families still contain sequences that are very similar. This poses problems when trying to place overlapping segments accurately.

 7. To clone a dinosaur would require: purifying DNA; amplifying all the sequences and piecing into chromosomes; putting all the chromosomes into the nucleus of an egg of a closely related species; precise development of the egg into a dinosaur.

8. Development is a program in which a three-dimensional collection of cells shapes itself over time. Each step of the program requires control by specific genes and proteins. One mistake can lead to malformation or death of the embryo.

9. When the egg forms, in most cases a number of genes are transcribed to RNA before fertilization. These RNA copies in the cytoplasm give the developing egg a "jump start" before the nuclear genes are expressed. Therefore, the egg cytoplasm contains genetic information from the mother. The genes involved are called maternal effect genes.

10. Correct development of an embryo requires precise regulation and timing of gene expression. The regulation of gene expression is tremendously subtle. A small sequence of base pairs to one side of a gene will bind to a specific regulatory protein, which recognizes the precise shape of the cleft of DNA helix at that particular sequence. If one or two base pairs are changed (mutated), the embryo will fail to develop properly.

11. After a messenger RNA molecule is transcribed from DNA, its sequence of bases (A, C, G, U—uracil replacing thymine) is translated by ribosomes into protein code: three DNA bases per amino acid of the protein. There are twenty essential amino acids.

12. Each kind of amino acid has to be synthesized within the cells of the organism, or consumed in food. Amino acids are synthesized by specific enzymes, encoded by specific genes. If a strain of organism is mutant for a enzyme needed to make an amino acid, it must consume food containing the amino acid. This kind of strain is called an auxotroph.

13. In some species of vertebrates, organisms can change sex during their development; typically females develop into males. This means that females contain the molecular components of both male and female development. Enviromental factors, such as absence of males, can stimulate the sex change. Examples are found in fish, amphibians, and reptiles.

 Development of an Organism           >>Top>>
 
1.  Sexual organisms produce haploid (1N) germ cells, which develop into sperm or eggs. The nucleus of each germ cell contains only one copy of each chromosome. Sperm and egg nuclei each carry equivalent amounts of genetic information, except for the X or Y chromosome contributed by the sperm.

2.  The cytoplasm of sperm develops into a specialized structure for swimming and delivery. It contributes no cytoplasm to the offspring. The egg, however, provides greatly expanded cytoplasm, including RNA expressed from maternal-effect genes. The egg also contributes mitochondria, which use oxygen to metabolize food for the cell.

    3.  Mitochondria have their own circular chromosomes, with a small number of genes. Genetic traits carried on the mitochondrial chromosome—including some defects leading to disease—are passed on only by mothers, to all of the mother=s children.

    4.  In humans, nuclear chromosomes carry many molecular modifications, such as methyl groups. The sperm and egg carry different patterns of modifications. This is called imprinting. Both male and female patterns of imprinting are needed for the fertilized egg to develop successfully as an embryo.

    5.  When the sperm enters the egg, its nucleus has to join the egg nucleus to restore a diploid chromosome number (2N). A chemical reaction is triggered in the egg cytoplasm to block any other sperm from entering and creating an abnormal chromosome number. Failure of this blocking reaction leads to abnormal development and spontaneous abortion.

    6.  The fertilized egg undergoes a precisely timed series of cellular divisions (cleavages). The ball of cells hollows out to form a blastula.

    7.  Part of the blastula pokes in (gastrulation) to form an inner layer of cells called the ectoderm; the layer remaining outside is called the ectoderm. This stage of development is called the gastrula.

    8.  Between the ectoderm and endoderm, cells migrate to form the mesoderm layer. The three layers of cells eventually differentiate to produce the following organs:
     

      A.  Ectoderm—Outer skin, sweat and milk glands, nervous system

      B.  Mesoderm—Muscles, skeleton, dermis of skin, circulatory system, gonads

      C.  Endoderm—Digestive tract, excretory system

    9.  The primordial germ cells (precursors to sperm or eggs) differentiate very early in human development, before the gonad organs form. The germ cells separate themselves from the back of the embryo, then have to migrate all the way up the gut into the genital ridges, where the gonads will form. If the germ cells get "lost," then gonads will form, outwardly normal; but the person will be sterile, unable to produce children.

    10.  Many genes and gene products interact with each other to control the sequence of development. Proteins expressed from genes in one part of the embryo can move to an adjacent part of the embryo and cause the cells to change shape. An example is when special cells beneath the ectoderm induce it to neurulate, forming the nervous system.

    11.  Alongside the neurulating ectoderm (neural plate) form blocks of cells called somites. The somites develop into muscle and bone.

    12.  Developmental genes often are pleiotropic; one gene may have different effects on different organs at different times. Therefore, mutation in one gene can have various effects on development of the embryo.

    13.  Why did organisms evolve aging? Natural selection favors genes that enhance function early in development and maturation, even if the same genes are detrimental later in life, after the organism has produced children.
     

Chromosomes, Speciation, and Artificial Selection       >>Top>>
    1.  Two populations can become reproductively isolated by several means: geographic separation, behavioral differences, anatomical incompatability, or chromosome rearrangement.

    2.  Plants can tolerate larger chromosome anomalies than animals. New species have arisen through polyploidy, doubling or tripling of the entire set of chromosomes.

    3.  During duplication of chromosomes, two unrelated chromosomes may get stuck together; this is called translocation. The result is equivalent to one larger chromosome.

    4.  Animals, especially vertebrates, require very precise gene dosage (relative number of copies of each gene). Therefore, extra pieces of chromosome cannot be tolerated. Dramatic rearrangement of chromosomes, however, can be tolerated with little effect on viability, so long as the total information content is unchanged.

    5.  An individual carrying a translocation may grow completely normally, so long as its chromosomes contain the normal amount of genetic information despite the rearrangement. Mitosis will occur normally. During meiosis, however, crossing over of normal and translocated chromosomes may produce unbalanced gametes that cannot combine with normal gametes to produce the right number of chromosomes.

    6.  The progeny of an individual carrying a translocated chromosome will reproduce best with each other, combining gametes with the same chromosome structure. If their line of descent prospers, it will probably generate a new species. Human and other mammalian genomes show evidence of many such translocation events in our chromosomal history.

    7.  Human breeding of plants or animals, termed artificial selection, can mimic the mechanisms of natural selection to produce new populations, and even new species, with traits beneficial to human masters. All agricultural plants and animals are the product of artificial selection.

    8.  The simplest form of artificial selection is to selectively mate individuals containing a desired trait; such as, chickens produced by hens that lay a large number of eggs. To the extent that the desired trait is influenced by genetic variation, succeeding generations of the organism will show increasing degree of the desired trait.

    9.  In plants, polyploidy can be used to produce "instant species." Very distantly related species can be crossed in this way. Seedless variants can be created by crossing 2N x 4N to yield 3N, which cannot produce gametes with even chromosome dosage.

    10.  Suppose a breeder wants to improve a domesticated strain of animal or plant by incorporating one particular trait of a related species in the wild. First, cross the two species and obtain progeny, even if only a few. Then breed these progeny back to the domesticated species, selecting offspring that retain the one desired trait from the wild species. Repeatedly breed them back to the domesticated species, until only the one desired trait remains from the wild species.

    11.  Some designers of computer software are now following logic analogous to "artificial selection" to develop new kinds of software. Programs are "mutated" in various ways, then allowed to run, and the "most fit" programs are selected for further mutation.

    12.  New computer structures are being designed to mimic biological processes, replacing "yes-or-no" logic with probabilistic circuits that allow the potential for "mistakes;" the circuit then "learns" from its mistakes. Such a circuit, called a neural net, achieves only approximate solutions to problems, but may come up with unexpectedly creative results.

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