Chapter XVII

Darwin establishes that the Galapagos archipelago consists of ten principal islands formed entirely of volcanic rock, situated under the Equator 500-600 miles west of America, with an estimated 2,000 craters throughout.

Darwin observes that all examined tuff-craters have their southern sides broken down or removed due to wave action from trade winds and Pacific swells during their formation in the sea.

Despite being on the equator, the islands have a moderate climate due to cold polar currents, with little rain, sterile lower regions, and lush vegetation in upper elevations above 1,000 feet.

Darwin describes landing on Chatham Island and finding the landscape dominated by leafless-appearing bushes despite the plants being in full leaf and flower, with a vegetation type similar to Fernando Noronha.

Darwin documents the numerous small volcanic cones with craters, the strange landscape, and his encounter with large tortoises among the black lava and leafless vegetation.

Darwin describes a small political prison colony of 200-300 people of color established six years prior, with vegetation improving at higher elevations and food sources including tortoises, wild pigs, and goats.

Darwin notes historical accounts of enormous tortoise harvests by ships and colonial hunters, with a single frigate reportedly taking 200 tortoises in one day.

Darwin describes immense lava flows at Albemarle Island and discovers a crater containing a salt-lake with crystallized salt deposits, contrasting the clear blue water with its briny composition.

Darwin is left on James Island for a week where he observes larger trees than on other islands and a damp upper region supporting vigorous vegetation and water-rails.

Darwin visits a salina where salt is obtained from a shallow lake at the bottom of a tuff-crater, featuring crystallized white salt and bright green succulent plants.

Darwin records high temperatures during his stay, with tent readings reaching 93°F, open air readings of 85°F, and sand temperatures reaching 137°F or higher.

Darwin notes that most organisms are aboriginal creations found nowhere else, show differences between islands, yet all bear marked relationship to America despite oceanic separation.

Darwin discusses the single indigenous mouse species confined to Chatham Island and a rat at James Island, speculating on whether they were imported or represent new varieties.

Darwin catalogs twenty-six land bird kinds, mostly peculiar to the archipelago, including a hawk, owls, finches, and mocking-thrushes, with detailed structural descriptions.

Darwin presents the most striking observation: thirteen finch species showing perfect gradation in beak size from hawfinch to warbler-sized, suggesting modification from an original species.

Darwin speculates that the diversity of finch structures within one small related group might suggest an original species modified for different ecological ends.

Darwin notes that only eleven water-bird kinds were found with few being new species, reflecting the greater range these orders have globally compared to terrestrial birds.

Darwin observes that many species are smaller or darker than their mainland counterparts, suggesting environmental causes rather than equatorial heat producing brilliant coloration.

Darwin emphasizes that reptiles, especially tortoises and lizards in extraordinary numbers, replace herbivorous mammals in a way unique globally and reminiscent of Secondary epochs.

Darwin identifies one small South American lizard species and two Amblyrhynchus species confined to the islands, plus one snake species identical to a Chilean species.

Darwin attributes the remarkable absence of frogs and toads on oceanic volcanic islands to the vulnerability of frog spawn to salt water compared to the protected eggs of lizards.

Darwin establishes that tortoises are found throughout the archipelago, preferring damp upper regions but also inhabiting lower arid areas, with evidence of their enormous abundance.

Darwin documents that tortoises in arid regions feed on succulent cactus while those in damp regions eat tree leaves, berries, and lichen.

Darwin describes how tortoises depend on water sources at the islands' centers, creating well-worn paths from springs to the coast, and their drinking behavior.

Darwin explains that tortoise bladders store water collected at springs and gradually decrease in purity, with inhabitants using this fluid for drinking during droughts.

Darwin measures tortoise walking speed at 360 yards per hour (four miles per day) and notes they travel day and night to reach their destinations.

Darwin describes tortoise breeding season, the male's audible roar heard over a hundred yards away, and female egg-laying behavior in sandy or rocky areas.

Darwin notes that tortoise eggs are white and spherical, larger than hen's eggs, and hatchlings fall prey to buzzards while adults die from accidents.

Darwin observes that tortoises appear deaf and reflexively withdraw when approached, demonstrating their defensive response to sudden proximity.

Darwin describes capture methods where hunters check fat deposits via incisions, and notes multiple uses of tortoise flesh and rendered oil.

Darwin argues the tortoise is indigenous to the Galapagos based on its distribution across all islands and historical accounts, though now widely distributed elsewhere.

Darwin identifies the Amblyrhynchus as a remarkable genus confined to the archipelago with two species: one aquatic and one terrestrial.

Darwin establishes that the aquatic Amblyrhynchus is common on all islands, confined to rocky sea-beaches, never found more than ten yards inland.

Darwin describes the marine lizard's hideous black coloring, flattened tail, webbed feet, typical length of one yard with some reaching four feet.

Darwin demonstrates the lizard's excellent swimming ability through serpentine body movement, noting an anecdote of one surviving submersion with heavy weight.

Darwin notes that the lizard's strong claws and limbs are perfectly suited for crawling over rugged fissured lava rocks forming the coastline.

Darwin's stomach dissections reveal the marine lizard feeds almost exclusively on minced sea-weed, likely obtained from the sea bottom at distance from shore.

Darwin proposes that the marine lizard's occasional sea-going is explained by the need to harvest sea-weed from deeper water away from shore.

Darwin identifies the remarkable anomaly that despite aquatic adaptations, the lizard refuses to enter water when frightened and must be driven to shore.

Darwin documents the lizard's counterintuitive behavior of returning directly to shore even when thrown into pools, attempting to hide in sea-weed but ultimately retreating to dry rocks.

Darwin hypothesizes that the marine lizard's refusal to enter water when frightened may reflect a hereditary instinct because shore predators are absent while sharks threaten at sea.

Darwin notes few small individuals observed during October visit, suggesting breeding season had not commenced, with locals ignorant of egg-laying location.

Darwin introduces the terrestrial species with round tail and unwebbed toes, confined to the central archipelago islands of Albemarle, James, Barrington, and Indefatigable.

Darwin notes the terrestrial lizard's absence from southern and northern islands, suggesting creation in the archipelago's center with limited dispersal.

Darwin observes the terrestrial lizard inhabits both high damp regions and lower sterile districts, with abundance evidenced by extensive burrow systems.

Darwin describes the terrestrial lizard as ugly with yellow-orange undersides and reddish-brown upper parts, resembling the marine species but weighing 10-15 pounds.

Darwin provides detailed observation of how the lizard excavates burrows using alternating front and hind legs, with the soft tuff creating unstable ground.

Darwin provides anecdotal evidence of watching a terrestrial lizard dig and then pulling its tail, observing its puzzled response to the disturbance.

Darwin observes the lizard feeds by day near its burrow, moves slowly except downhill, and displays defensive head-nodding when watching intruders.

Darwin notes the lizard is not genuinely timorous despite threatening posture, as ground-stamping causes retreat and they inflict severe bites when provoked.

Darwin observes that pairs of terrestrial lizards will fight and bite each other severely when confined together, demonstrating inter-individual aggression.

Darwin documents the terrestrial lizard's consumption of succulent cactus in lower regions, rarely tasting water, with observed playful food competition.

Darwin observes the deliberate eating behavior of terrestrial lizards and documents a finch feeding simultaneously at the opposite end of a cactus piece.

Darwin's dissections show the terrestrial lizard stomach contains vegetable fibers and tree leaves, especially acacia, with upper region inhabitants eating guayavita berries.

Darwin documents terrestrial lizards climbing stunted trees for acacia leaves and observes pairs browsing together on branches several feet above ground.

Darwin notes that cooked terrestrial lizard yields white meat appreciated by those without prejudice, and Humboldt noted similar usage in South American dry regions.

Darwin reports that upper region lizards drink water while lower region inhabitants do not, and unlike tortoises, do not travel upland for water.

Darwin notes that at the time of visit, females carried numerous large elongated eggs laid in burrows, which inhabitants harvested for food.

Darwin emphasizes both Amblyrhynchus species share general structure and herbivorous diet but feed on different vegetation, with adapted mouth form resembling tortoises.

Darwin highlights the remarkable nature of a well-characterized genus with marine and terrestrial species confined to a small region, with the aquatic species being unique as the only existing marine plant-eating lizard.

Darwin argues that the islands are remarkable for reptile dominance, with tortoises, turtles, and Amblyrhynchus replacing herbivorous mammals in an extraordinary manner comparable to Secondary epochs.

Darwin notes the paradox that despite arid climate and temperate conditions unsuitable for reptile abundance, the archipelago shows extraordinary reptile presence.

Darwin reports fifteen new fish species from twelve widely distributed genera, with Prionotus being exceptional as a genus otherwise found only on America's eastern side.

Darwin documents that land-shells are predominantly endemic with only one exception, while sea-shells show higher cosmopolitan distribution but with notable endemic component.

Darwin synthesizes shell data showing the Galapagos as a biogeographic junction where American species, Low Archipelago species, and endemic forms meet, creating a distinct conchological province.

Darwin laments the poor insect fauna, finding fewer specimens than in Tierra del Fuego despite tropical latitude, with dull coloration contradicting equatorial expectations.

Darwin catalogues 25 beetle species belonging to diverse families, with many new genera and species, mostly found nowhere else except those imported by ships.

Darwin reports 185 flowering plant species with 100 being new and endemic, making the archipelago a distinct botanical province though less distinctive than St. Helena or Juan Fernandez.

Darwin expresses surprise that more American species were not naturally introduced despite proximity and evidence of driftwood transport from the continent.

Darwin highlights 21 Compositae species with 20 endemic, belonging to 12 genera of which 10 are confined to the archipelago, demonstrating exceptional botanical uniqueness.

Darwin establishes that the Galapagos flora has undoubted Western American character with no Pacific affinity, making it zoologically part of America despite Pacific location.

Darwin emphasizes that the vast majority of land animals and over half of flowering plants are aboriginal productions, not merely immigrants from America.

Darwin articulates the central mystery: why do these geologically recent, volcanically-formed islands under unique climate have aboriginal inhabitants of American type when physically different from America?

Darwin notes that Cape de Verd Islands resemble the Galapagos far more closely in physical conditions but have African-impressed inhabitants, not American types.

Darwin recounts his discovery that different islands are inhabited by different sets of beings, first noted when the Vice-Governor mentioned tortoise variation between islands.

Darwin documents reports that tortoises differ between islands in size and other characters, with Captain Porter describing distinct shell forms between Charles and James Islands.

Darwin notes the marine Amblyrhynchus is larger at Albemarle Island and proposes different islands have representative species or races, as with tortoises.

Darwin documents that mocking-thrushes from different islands belong to different species: Mimus trifasciatus at Charles, M. parvulus at Albemarle, and M. melanotis at James and Chatham.

Darwin suspects finch species of the sub-group Geospiza are confined to separate islands, which would explain the singularly large number of species within this small archipelago.

Darwin establishes that two Cactornis and two Camarhynchus sub-groups each have island-specific species, with collections from James Island differing from Chatham or Charles Island specimens.

Darwin notes that the law of inter-island species differentiation does not apply to land-shells, which show different geographic patterns than other organisms.

Darwin records that insects with documented localities show no overlap between islands, consistent with the general pattern of inter-island endemism.

Darwin introduces botanical data showing the aboriginal plants of different islands are wonderfully different, emphasizing Dr. Hooker's authoritative analysis.

Darwin acknowledges limitations in his collections and notes that Leguminosae family requires further study, though the basic pattern of inter-island difference holds.

Darwin presents data showing James Island's 71 species include 38 endemic Galapagos plants, with 30 of these confined exclusively to James Island.

Darwin demonstrates that Albemarle, Chatham, and Charles Islands follow the same pattern as James, with the majority of endemic Galapageian plants confined to single islands.

Darwin exemplifies inter-island endemism through Scalesia, an arborescent Compositae genus with six species each confined to separate islands with no overlap.

Darwin notes Euphorbia has eight species with seven endemic and none overlapping between islands, as with Acalypha and Borreria genera showing similar patterns.

Darwin emphasizes Compositae species are particularly local and restricted, with Dr. Hooker providing multiple striking illustrations of inter-island species difference.

Darwin establishes that the law of island-specific species applies both to archipelago-endemic genera and widely distributed genera, with tortoises, mocking-thrushes, finches, and Amblyrhynchus showing this pattern.

Darwin argues the distribution would be less remarkable if islands had entirely different genera, but the remarkable fact is that similar genera have island-specific representative species.

Darwin proposes that representative species or well-marked races, whether ultimately classified as species or varieties, are of equal interest to the philosophical naturalist.

Darwin provides precise distances between islands—Charles 50 miles from Chatham, James only 10 miles from Albemarle—emphasizing their proximity despite species differences.

Darwin emphasizes that soil nature, land height, climate, and associated organisms are similar across islands, with no substantial differences in the two climate halves.

Darwin proposes that strong westerly and north-westerly ocean currents separate islands, preventing inter-island transport of organisms by sea.

Darwin notes the archipelago's freedom from gales means birds, insects, and light seeds are not blown between islands, reducing dispersal opportunities.

Darwin argues that the archipelago's recent volcanic origin and profound ocean depths make island union unlikely, making geological isolation probably the most important consideration.

Darwin expresses wonder at the amount of creative force displayed on small barren islands and its diverse yet analogous action across proximate points.

Darwin refines his earlier metaphor, proposing the archipelago should be called satellites that are physically similar, organically distinct, yet intimately related to each other and America.

Darwin promises to conclude with an account of the extreme tameness of birds, a distinctive characteristic of terrestrial species throughout the archipelago.

Darwin documents that all terrestrial bird species including mocking-thrushes, finches, wrens, flycatchers, doves, and buzzards are extremely tame, allowing approach within killing distance.

Darwin provides specific examples of birds alighting on vessels in hand and nearly allowing capture, with testimony that birds were even tamer historically.

Darwin cites early explorers Cowley and Dampier who documented birds so tame they alighted on people and could be taken in large numbers, suggesting tameness has decreased.

Darwin notes the surprising fact that birds remain relatively tame despite 150 years of visitation by whalers and sailors deliberately killing them for entertainment.

Darwin documents a boy at Charles Island colony killing doves and finches by a well for food, having made a habit of waiting there daily.

Darwin proposes that birds disregard humans because they have not learned that man is more dangerous than tortoises or Amblyrhynchus, as they ignore herbivores.

Darwin cites the Falkland Islands as offering similar bird tameness despite presence of foxes, hawks, and owls, suggesting predator absence is not the cause.

Darwin lists multiple Falkland bird species showing tameness including Polyborus, snipe, geese, thrush, bunting, and hawks despite predator presence.

Darwin observes that upland geese at Falklands take precautions building on islets showing fox-awareness but remain tame toward humans, demonstrating selective fear.

Darwin contrasts the Falklands tame water-fowl with their wild behavior in Tierra del Fuego where persecuted by indigenous peoples for centuries.

Darwin compares hunting ease in Falklands where sportsmen kill many geese in a day with Tierra del Fuego difficulty comparable to hunting English wild geese.

Darwin cites Pernety's 1763 account showing Falkland birds as formerly much tamer, with Opetiorhynchus perching on fingers and killing ten with a wand in half-hour.

Darwin proposes Falkland birds learned caution faster than Galapagos birds due to more frequent vessel visits and prolonged colonization periods.

Darwin notes the black-necked swan, a migratory species, remained wild even in Pernety's era, presumably bringing learned wariness from foreign countries.

Darwin cites Du Bois's account of all Bourbon birds (except flamingoes and geese) being extremely tame in 1571-72, capturable by hand or stick.

Darwin documents Carmichael's account of Atlantic island birds so tame they could be caught with a hand-net, demonstrating global pattern of island bird tameness.

Darwin concludes from multiple examples that bird wildness toward man is a particular instinct directed at humans, not dependent on general caution from other dangers.

Darwin proposes that wildness is not acquired quickly by individual birds even when persecuted, but becomes hereditary over generations.

Darwin notes that while domesticated animals show new mental habits becoming hereditary, natural animals rarely demonstrate acquired hereditary knowledge.

Darwin argues that English birds' universal fear of humans, despite few nestlings being injured annually, demonstrates innate rather than learned basis.

Darwin notes that despite many individuals at Galapagos and Falklands being pursued and injured, they have not learned to fear man, contradicting learning hypothesis.

Darwin concludes that introduction of new predators must cause devastating havoc before indigenous instincts adapt to the stranger's power, showing importance of inherited instincts.