Editing Alfred Russel Wallace (section)

== Other scientific contributions ==

=== Biogeography and ecology ===
[[File:Wallace03.jpg|thumb|upright=1.5|A map of the world from ''The Geographical Distribution of Animals'' shows Wallace's six biogeographical regions.|alt=map of the world divided into Wallace's six biogeographical regions]]

In 1872, at the urging of many of his friends, including Darwin, [[Philip Sclater]], and [[Alfred Newton]], Wallace began research for a general review of the geographic distribution of animals. Initial progress was slow, in part because classification systems for many types of animals were in flux.{{sfn|Slotten|2004|p=301}} He resumed the work in earnest in 1874 after the publication of a number of new works on classification.{{sfn|Slotten|2004|p=315}} Extending the system developed by Sclater for birds—which divided the earth into six separate geographic regions for describing species distribution—to cover mammals, reptiles and insects as well, Wallace created the basis for the [[biogeographic realm|zoogeographic regions]] in use today. He discussed the factors then known to influence the current and past geographic distribution of animals within each geographic region.<ref name="Holt Lessard Borregaard 2013">{{cite journal |last1=Holt |first1=Ben G. |last2=Lessard |first2=Jean-Philippe |last3=Borregaard |first3=Michael K. |last4=Fritz |first4=Susanne A. |last5=Araújo |first5=Miguel B. |last6=Dimitrov |first6=Dimitar |last7=Fabre |first7=Pierre-Henri |last8=Graham |first8=Catherine H. |last9=Graves |first9=Gary R. |last10=Jønsson |first10=Knud A. |last11=Nogués-Bravo |first11=David |last12=Wang |first12=Zhiheng |last13=Whittaker |first13=Robert J. |last14=Fjeldså |first14=Jon |last15=Rahbek |first15=Carsten |display-authors=3 |title=An Update of Wallace's Zoogeographic Regions of the World |journal=[[Science (journal)|Science]] |volume=339 |issue=6115 |date=4 January 2013 |doi=10.1126/science.1228282 |pages=74–78|pmid=23258408 |bibcode=2013Sci...339...74H |s2cid=1723657 }}</ref>

These factors included the effects of the appearance and disappearance of land bridges (such as the one currently [[Great American Interchange|connecting North America and South America]]) and the effects of periods of increased glaciation. He provided maps showing factors, such as elevation of mountains, depths of oceans, and the character of regional vegetation, that affected the distribution of animals. He summarised all the known families and genera of the higher animals and listed their known geographic distributions. The text was organised so that it would be easy for a traveller to learn what animals could be found in a particular location. The resulting two-volume work, ''The Geographical Distribution of Animals'', was published in 1876 and served as the definitive text on [[zoogeography]] for the next 80 years.{{sfn|Slotten|2004|pp=320–325}}

The book included evidence from the fossil record to discuss the processes of evolution and migration that had led to the geographical distribution of modern species. For example, he discussed how fossil evidence showed that [[tapirs]] had originated in the [[Northern Hemisphere]], migrating between North America and Eurasia and then, much more recently, to South America after which the northern species became extinct, leaving the modern distribution of two isolated groups of tapir species in South America and Southeast Asia.{{sfn|Bowler|2013|p=152}} Wallace was very aware of, and interested in, the [[Quaternary extinction event|mass extinction of megafauna]] in the late [[Pleistocene]]. In ''The Geographical Distribution of Animals'' (1876) he wrote, "We live in a zoologically impoverished world, from which all the hugest, and fiercest, and strangest forms have recently disappeared".{{sfn|Wallace|1876|p=150}} He added that he believed the most likely cause for the rapid extinctions was glaciation, but by the time he wrote ''World of Life'' (1911) he had come to believe those extinctions were "due to man's agency".{{sfn|Wallace|1911|p=246}}

[[File:Wallace-line1.jpg|thumb|left|upright=1.7|The line separating the Indo-Malayan and the Austro-Malayan region in Wallace's ''On the Physical Geography of the Malay Archipelago'' (1863)|alt=map of Southeast Asia showing the Wallace line]]

In 1880, Wallace published the book ''Island Life'' as a sequel to ''The Geographical Distribution of Animals''. It surveyed the distribution of both animal and plant species on islands. Wallace classified islands into oceanic and two types of continental islands. Oceanic islands, in his view, such as the [[Galapagos]] and [[Hawaiian Islands]] (then called Sandwich Islands) formed in mid-ocean and never part of any large continent. Such islands were characterised by a complete lack of terrestrial mammals and amphibians, and their inhabitants (except migratory birds and species introduced by humans) were typically the result of accidental colonisation and subsequent evolution. Continental islands, in his scheme, were divided into those that were recently separated from a continent (like Britain) and those much less recently (like [[Madagascar]]). Wallace discussed how that difference affected flora and fauna. He discussed how isolation affected evolution and how that could result in the preservation of classes of animals, such as the [[lemur]]s of Madagascar that were remnants of once widespread continental faunas. He extensively discussed how changes of climate, particularly periods of increased glaciation, may have affected the distribution of flora and fauna on some islands, and the first portion of the book discusses possible causes of these great [[ice age]]s. ''Island Life'' was considered a very important work at the time of its publication. It was discussed extensively in scientific circles both in published reviews and in private correspondence.{{sfn|Slotten|2004|p=361}}

=== Environmentalism ===
Wallace's extensive work in biogeography made him aware of the impact of human activities on the natural world. In ''Tropical Nature and Other Essays'' (1878), he warned about the dangers of deforestation and soil erosion, especially in tropical climates prone to heavy rainfall. Noting the complex interactions between vegetation and climate, he warned that the extensive clearing of [[rainforest]] for coffee cultivation in Ceylon (now called [[Sri Lanka]]) and India would adversely impact the climate in those countries and lead to their impoverishment due to soil erosion.{{sfn|Slotten|2004|pp=352–353}} In ''Island Life'', Wallace again mentioned deforestation and [[invasive species]]. On the impact of European colonisation on the island of [[Saint Helena]], he wrote that the island was "now so barren and forbidding that some persons find it difficult to believe that it was once all green and fertile".{{sfn|Wallace|1881|pp=283–284}}  He explained that the soil was protected by the island's vegetation; once that was destroyed, the soil was washed off the steep slopes by heavy tropical rain, leaving "bare rock or sterile clay".{{sfn|Wallace|1881|pp=283–284}} He attributed the "irreparable destruction"{{sfn|Wallace|1881|pp=283–284}}  to feral goats, introduced in 1513. The island's forests were further damaged by the "reckless waste"{{sfn|Wallace|1881|pp=283–284}}  of the East India Company from 1651, which used the bark of valuable redwood and ebony trees for tanning, leaving the wood to rot unused.{{sfn|Wallace|1881|pp=283–284}} Wallace's comments on environment grew more urgent later in his career. In ''The World of Life'' (1911) he wrote that people should view nature "as invested with a certain sanctity, to be used by us but not abused, and never to be recklessly destroyed or defaced."{{sfn|Wallace|1911|p=279}}
[[File:Wallace-2.jpg|alt=Title page to Man's Place in the Universe (1903)|thumb|229x229px|Title page to ''Man's Place in the Universe'' (1903)]]

=== Astrobiology ===
Wallace's 1904 book ''[[Man's Place in the Universe]]'' was the first serious attempt by a biologist to evaluate the [[planetary habitability|likelihood of life on other planets]]. He concluded that the Earth was the only planet in the [[Solar System]] that could possibly support life, mainly because it was the only one in which water could exist in the [[liquid phase]].<ref name="Kutschera 2012">{{cite journal |last=Kutschera |first=Ulrich |author-link=Ulrich Kutschera |title=Wallace pioneered astrobiology too |journal=[[Nature (journal)|Nature]] |volume=489 |issue=7415 |year=2012 |doi=10.1038/489208e |pages=208 |pmid=22972286 |s2cid=4333070 |doi-access=free }}</ref> His treatment of [[Mars]] in this book was brief, and in 1907, Wallace returned to the subject with the book ''[[Is Mars Habitable?]]'' to criticise the claims made by the American astronomer [[Percival Lowell]] that there were [[Martian canals]] built by intelligent beings. Wallace did months of research, consulted various experts, and produced his own scientific analysis of the Martian climate and atmospheric conditions.{{sfn|Slotten|2004|p=474}} He pointed out that [[spectroscopic analysis]] had shown no signs of [[water vapour]] in the [[Martian atmosphere]], that Lowell's analysis of Mars's climate badly overestimated the surface temperature, and that low atmospheric pressure would make liquid water, let alone a planet-girding irrigation system, impossible.<ref>{{cite web |last=Wallace |first=Alfred |title=''Is Mars Habitable'' (S730: 1907) |url=http://www.wku.edu/~smithch/wallace/S730.htm |publisher=The Alfred Russel Wallace Page hosted by [[Western Kentucky University]] |access-date=13 May 2007 |archive-url= https://web.archive.org/web/20070405172431/http://www.wku.edu/~smithch/wallace/S730.htm |archive-date= 5 April 2007 |url-status=live}}</ref> Richard Milner comments that Wallace "effectively debunked Lowell's illusionary network of Martian canals."<ref>{{cite web|title=A Wet Red World? The Search for Water on Mars Goes On |last=Milner |first=Richard |work=Astrobiology Magazine |date=4 November 2011 |url=http://www.space.com/13510-water-mars-search-life.html |access-date=22 November 2012}}</ref> Wallace became interested in the topic because his anthropocentric philosophy inclined him to believe that man would be unique in the universe.{{sfn|Shermer|2002|p=294}}