Are humans special after all

In chapter 15 we suggested that "human intelligence" is an evolutionary freak, so improbable that nothing like it has arisen elsewhere else in the universe. We repeated this claim in chapter 17. We have also argued that although any animal capable of intelligent behaviour can be said to have a mind, humans are unique in being able to express and articulate the contents of their minds.

This conclusion is scarcely original or startling. All we have done in the past three chapters is to relate mind to brain and to evolution in a rather novel (though in no way remarkable) way. But in conjunction with our claim for human uniqueness, perhaps this does lead to a surprising inference. If humans are unique in the nature and articulation of their minds, and if they have no counterpart anywhere else in the universe, then the capacity to abstract and express mental processes is absolutely unique to us. If so, the evolutionary emergence of our species has added something entirely new to the universe. This is an optimistic inference, very much at odds with the existential pessimism that seems to have become part of the legacy of science.

Galileo kicked the immovable Earth into orbit around the sun. To his more conservative contemporaries, his temerity seemed to denigrate humankind. Since Galileo's day the Earth, and the sun around which it rotates, and even the galaxy of which the sun is one tiny part, have grown more and more insignificant in relation to the universe as a whole. Many people find this depressing. The Earth is utterly insignificant, they say, so what is the point of our being here?

Darwin kicked the Aristotelian ladder of nature from under the living world. In the process, he revealed that the human species is a late-comer among countless millions of species of organisms, inherently no more special than any other, and guaranteed to share the ultimate fate of all -extinction. Many people find this even more depressing than the apparent insignificance of our planet.

What Galileo, Darwin and their successors told us is perfectly correct. Nevertheless, if our argument in the past four chapters is valid, our species is unique and special. If we are right, then only on our apparently insignificant planet, and in our apparently insignificant species, is there such a thing as a self-expressing mind. Without us, the cosmos would have no mind that could record its existence.

What we, as a species, have done with this cosmically unique innovation has not always been interesting or commendable. However, some of it has. What we shall do with it in the future is another matter.

In the meantime, we can enjoy our unique capability. Sitting in the quiet woodland at sunrise, marvelling at the primrose and the oak-tree, the beetle and the weasel, we can reflect on the fact that nowhere else in the universe is there an entity with this capacity for marvelling, or for inquiring and understanding what "life" is; or for inquiring what constitutes the "capacity for marvelling".

GLOSSARY AND PRONUNCIATION GUIDE

NOTE: cross-references to other parts of this guide are indicated by the use of UPPER CASE letters. Where pronunciation is given, the stressed syllable is indicated by the mark'.

Action potential: Brief electric impulse that travels along the AXON in a NEURONE.

Amino acid (pron. A-my'-no acid): A building block (monomer unit) of a PROTEIN molecule.

Amygdala (pron. A-mig'-duh-la): Small piece of the brain below the temporal lobe responsible for emotions of anger and fear. (Greek: amygdale = almond.)

Anabolism (pron. A-nab'-ole-ism): Any process by which biological molecules are manufactured in cells. (Greek: an = up, + METABOLISM.)

Archaea (pron. Ar-key'-a): PROKARYOTE group that includes the inhabitants of extreme environments. (Greek: archaios = ancient, arche = beginning.)

ATP = adenosine triphosphate: Molecule crucially involved in energy-requiring and energy-mobilising reactions in cells. (Greek: aden = gland.)

Axon: Extension of a NEURONE that carries ACTION POTENTIALS. (Greek: axon = axis.)

Base: Part of a building block (monomer unit) of a nucleic acid; the other parts are phosphate and a type of sugar. Sequences of bases in DNA constitute genetic information. (Note: in chemistry, "base" has a different and more general definition, not relevant to this book.)

Biosphere: Parts of the Earth and atmosphere in which living things are found. (Greek: bios = life.)

Carbonaceous chondrite (pron. car-bon-ay'-shuss kond'-right): A

meteorite containing rounded granules with organic molecules. (Greek: chondros = grain, granule.)

Catabolism: Any process by which biological molecules are broken down to release energy. (Greek: cata = down, + METABOLISM.)

Catalysis (pron. Cat-a'-liss-iss): Chemical change brought about by a substance (in biology, an ENZYME) that is itself unchanged. (Greek: cata = down, lysis = dissolution.)

Cell membrane: The ultra-thin barrier that divides the cell from its environment.

Cell wall: The tough shell around a prokaryote or a plant or fungal cell.

Chloroplast (pron. Kloa'-row-plast): A green body inside a plant cell that is responsible for photosynthesis. (Greek: chloros = pale green, plasma = body.)

Coelenterazine (pron. See-lent'-er-a-zeen'): A molecule that binds oxygen, derived from marine organisms such as coelenterates. (Greek: koilos = hollow, enteron = intestine.)

Cyanobacteria (pron. Sigh-an'-no-bacteria): Prokaryotes containing chlorophyll, the green pigment essential for photosynthesis. (Greek: kyanos = blue.)

Cytoskeleton (pron. Sigh'-toe-skeleton): The fibrous structures in cells responsible for shape, movement and some transport processes. (Greek: kytos = vessel, hollow.)

Dendrite: Branching projection of a NEURONE. (Greek dendron = tree.)

DNA: Deoxyribonucleic acid. The substance of which genes are made.

Ecosystem: A community of organisms, their environment and the interactions among them. (Greek: oikos = house.)

Ediacara fauna: The earliest known multicellular organisms, dating from the late Precambrian. (Named after the Ediacara Hills, Flinders Range, South Australia.)

Endocytosis (pron. End'-oh-sigh-toe'-siss): Uptake of material into cells by pinching off of membrane vesicles. (Greek: endo = within, kytos = vessel, hollow.)

Enhancer: Region of DNA that binds TRANSCRIPTION FACTORS, modifying the rate of TRANSCRIPTION of one or more genes.

Enzyme: A biological CATALYST. Most enzymes are proteins; a few are RNA.

Eukaryote (pron. You-car'-ry-oat): An organism consisting of one or more cells, each with its DNA packaged in a separate compartment, the NUCLEUS. (Greek: eu = well (formed), karyon = kernel.)

Exon: Segment of a gene that codes for part of a protein. (Latin: ex = out of, + Greek neuter suffix -on.)

Exon shuffling: A DNA rearrangement in which an EXON of one gene is inserted into a different gene.

Forebrain: The most recently evolved part of the brain, including the cerebral hemispheres.

Frontal lobe: Part of the cerebral hemispheres behind the forehead. In humans, associated with (among other things) the capacity for abstract thought.

Gene duplication: A DNA rearrangement in which two or more copies of the same gene are inserted into the DNA. (Greek: -genes = born.)

Gene pool: The stock of genes and gene variants found in an inbreeding POPULATION.

Genome: The total stock of genes in an individual (assumed to be a typical member of the species.)

Hindbrain: Evolutionarily oldest part of the vertebrate brain. Includes the cerebellum, which is involved in the control of bodily movements, and the medulla oblongata, a part of the brain stem involved in controlling respiration and heart rate.

Hydrocarbon: A chemical substance consisting only of the elements hydrogen and oxygen.

Immediate-early genes: Genes that are activated first during a developmental process. In turn they activate many other genes, directly or indirectly.

Initiation complex: Assembly of proteins that enables RNA POLY-MERASE II to begin TRANSCRIPTION at the start of a gene.

Intron: A non-coding segment of a gene; opposite of EXON.

Kaolinite: A flaky aluminium silicate mineral produced by the breakdown of feldspar.

Lysosome (pron. Lie'-so-soam): A membrane-bound particle containing enzymes necessary for intracellular digestion. (Greek: lysis = dissolution, soma = body.)

Metabolic pathway: A sequence of chemical reactions in a cell that converts one sort of molecule into another.

Metabolon: An assembly of enzymes needed for (part of) a metabolic pathway.

Midbrain: Part of the brain dominant in reptiles. In mammals, links the forebrain and hindbrain and contains areas involved in emotional responses, pain, etc.

Mitochondria (pron. My'-toe-kon'-dree-a): The energy-producing bodies in EUKARYOTIC cells. (Singular = mitochondrion. Greek: mitos = thread, chondros = granule.)

Montmorillonite (pron. Mont-mur-ill'-o-night): A clay mineral chemically similar to KAOLINITE; a constituent of Fuller's Earth. (Named after Montmorillon, France.)

Mutation: Genetic change. (Latin: mutare = to change.) Neurone: A nerve cell. (Greek: neurone = nerve.)

Neurotransmitter: A chemical released from an AXON terminus that conveys the nerve impulse across a SYNAPSE.

Nucleic acid: A polymer of which the building blocks (monomer units) are molecules consisting of a sugar, a phosphate and one of four bases: A, G, C, T in DNA; A, G, C, U in RNA.

Nucleus: The part of an EUKARYOTIC cell that contains most of the DNA (genes).

Occipital lobe: Part of the cerebral cortex at the back of the head.

Parietal lobe: Part of the cerebral cortex at the top of the head. (Latin: paries = wall.)

Polymer: A molecule made by joining many smaller molecules (monomer units or "building blocks") together. (Greek: poly = many, meroi = parts.)

Polymerase: An enzyme that joins "building block" molecules together to make a biological polymer.

Population: All the members of a species that are capable (for geographical and other reasons) of breeding with one another.

Prokaryote (pron. Pro-car'-ry-oat): A single-celled organism that does not have its DNA packaged in a separate nucleus. (Greek: pro = before + karyon = kernel.)

Protein: A polymer of AMINO ACIDS. Proteins are responsible for all the structural, functional and informational features of a cell.

Protist: A unicellular EUKARYOTE. (Greek protistos = the very first.)

Pseudogene: A degenerate copy of a gene incapable of being transcribed.

Receptor: Structure on a cell (surface) that binds specifically to a stimulus (signal) molecule and initiates a response in the cell.

Resting potential: Electrical potential between the inside and the outside of a NEURONE or other cell.

Retrotransposon (pron. Ret'-row-trans-po'-zon): A piece of DNA containing retroviral and other genes that can move from place to place in the genome.

Ribosome (pron. Righ'-bow-soam): An intracellular machine for making proteins according to the instructions in messenger RNAs.

RNA: Ribonucleic acid. Includes messengers that carry the instructions in a gene to the protein-making machinery (RIBOSOMES).

RNA polymerase: An ENZYME for making RNA (i.e. for TRANSCRIBING it from a sequence in DNA).

Signalling pathway: A sequence of reactions in a cell that is initiated by the binding of a stimulus molecule to a receptor. A signalling pathway can lead to various changes in cell structure and metabolism and in gene expression.

Simple-sequence DNA: A short segment of DNA (3-10 bases) that is repeated hundreds or even thousands of times in the GENOME.

Spirochaete (pron. Spy'-row-keet): A type of spirally coiled bacterium that swims, usually by making "wriggling" movements. (Greek: speira = coil, chaite = hair.)

Symbiosis (pron. Sim-buy-owe'-siss): Mutual dependence between organisms of two or more different species. (Greek: syn = together, bios = life.)

Synapse: The tiny gap between one NEURONE and another. (Greek: syn = together, haptein = to fasten.)

Taxonomy: Biological classification. (Greek: taxis = order, nomia = distribution.)

Temporal lobe: Lobe on each side of the cerebral cortex of the brain. (Latin tempus = temple.)

Terminal arborisation: The branching of an AXON that allows it to form SYNAPSES with many other NEURONES. (Latin: arbor = tree.)

Transcription: The process by which a messenger RNA copy of a gene is made.

Transcription factor: A PROTEIN that binds to an ENHANCER region of DNA and alters the rate of TRANSCRIPTION of one or more genes.

Transposon: A piece of DNA that can move to a different position on a chromosome or to a different chromosome, altering the cell's genetic makeup.

Vacuole: A small fluid-filled cavity in a cell. (French: little vacuum.)

Vesicle: A roughly spherical structure inside a cell caused by the pinching off of a small piece of membrane. (Latin: vesica = bladder, blister.)

FURTHER READING

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