Biology: Evolution of Life

Sections on this page: The Evolutionary Time ScaleNaming and Classifying Plants and AnimalsGeneration, Struggle and ExtinctionEvolution by Natural SelectionMore About Evolution.


The Evolutionary Time Scale

Here is a summary of the sequence of evolution. The figures are in units of millions of years since first known appearance.

3500 Microbes (procaryotic)
2000 Single-celled creatures (eucaryotic)
_670 Multi-celled creatures
_540 Shell-bearing animals
_490 Vertebrates (fishes)
_350 Amphibians
_310 Reptiles
_200 Mammals
__60 Nonhuman primates
__25 Earliest apes
___4 Human ancestors (Australopithecine)
___0 Modern humans 0.15 (150,000 years)


Naming and Classifying Plants and Animals

Aristotle (−384 - −322) was one of the first to study plants and animals closely, his writings mention 560 animal species. He described the internal anatomy of crabs, lobsters, fish, squid and sea-urchin. He recognised a 'chain of being' from minerals, through plants to animals and humans. Theophrastus (c.−372 - −287) specialised more in botany, classifying almost 500 plants and describing their structure and cultivation.

Pedanius Dioscorides (c.20 - 90), a surgeon with the Roman army, gathered the knowledge then available on medicinal plants in his De Materia Medica.

Robert Hooke (1635 - 1703) and Antoni van Leeuwenhoek (1632 - 1723) were the first microscopists.

R. J. Camerarius (1665 - 1721) in 1694 showed experimentally that plants reproduce sexually; a deposit of pollen on stigmas being needed if a plant is to set seed.

Thomas Fairchild around 1720 produced the first man-made inter-specific hybrid by cross-pollinating a carnation and a sweet william.

Carl von Linné (Carolus Linnaeus 1707 - 1778) introduced the two-part name system of genus and species for any plant or animal in his Systema Natura 1735. His works describe nearly 10,000 different species.


Generation, Struggle and Extinction

Many people, including noted biologists such as Georges-Louis Leclerc, Comte de Buffon Histoire Naturelle 1749 and John Needham Nouvelles Observations Microscopiques 1750, thought new life forms could appear from decaying matter by spontaneous generation. This was despite the work of Leeuwenhoek and Francesco Redi (1626 - 1697) in 1668 who had shown that maggots hatch from egg-laying flies. Lazzaro Spallanzani (1729 - 1799) in 1765 did further microscopic studies to refute the idea, but the debate was not finally settled until the work of Louis Pasteur in 1860.

C. K. Sprengel & & & (1750 - 1816) in 1793 made observations on the pollination of plants by insects.

The surgeon John Hunter (1728 - 1793) and the naturalist Georges Cuvier & (1769 - 1832) began comparative anatomy by realising that all vertebrate animals have a common skeletal plan, allowing the assembly of incomplete sets of fossil bones into sensible forms. Cuvier in 1796 showed that the extinct Megatherium of South America was a giant ground sloth. In 1804 he reconstructed an extinct marsupial mammal and the tapir-like Palaeotherium.

Evolutionary views were expressed by Jean-Baptiste Lamarck & & & & (1744 - 1829) and Etienne Geoffroy St Hilaire (1772 - 1844). Lamarck coined the term 'biology' and expounded a theory of gradual evolution of living things in his Philosophie Zoologique 1809, based on the principle that characteristics acquired by parents (e.g. greater weight, height or strength) could gradually influence the nature of their offspring.

William Buckland & & & &(PDF) (1784 - 1856), Gideon Mantell & & & (1790 - 1852) and Mary Anning & & & & & & (1799 - 1847) found fossils of giant reptiles, Iguanodon and Megalosaurus, which were named Dinosaurs by Richard Owen (1804 - 1892).

Thomas Robert Malthus & & & & & & (1766 - 1834) in 1798 published the first edition of his Essay on the Principle of Population & & & & which maintained that because population increases geometrically whereas food supply increases arithmetically mass starvation would result unless human numbers are kept in check by infant mortality, epidemics, famine, prostitution, and war. This was the beginning of theory of political economy. His work influenced the harsh poor law amendment act of 1834, and the ideas were also seen to apply throughout nature.

The 1799 - 1804 expedition of Alexander von Humboldt & (1769 - 1859) [see also the geology page] with the botanist Aimé Bonpland & & & (1773 - 1852) in equatorial South America collected an abundance of botanical and geological specimens, and introduced the concept of plants and animals being adapted to a specific environment.


Evolution by Natural Selection

All the above were influences on Charles Darwin (1809-1882) whose Origin of Species by means of Natural Selection was published in 1859. His three main theories are (1) that all the varied species of life arose from a common origin, (2) that there are inheritable variations that occur by chance, and (3) that the process leading to the development of different species is natural selection acting on these variations. That is, where there are competing species those better adapted to the environment will survive and produce more offspring.

Some attributes, like the peacock's tail or the antlers of a stag develop to help the animals compete to attract mates; this is a special case of natural selection called sexual selection, which he expounded in a later book The Descent of Man, and Selection in relation to Sex 1871.

Darwin also did extensive work on cross-pollination.

It may seem surprising that organs like the mammalian eye could have evolved by natural selection, but in fact there is evidence of a whole sequence of development from light sensitive spots in worms upwards.

Thomas Henry Huxley & (1825 - 1895) was one of the principal defenders of Darwin's theory of evolution by natural selection in public debate and realised the archaeopteryx discovered in 1860 and described anatomically by Owen, with its mixture of reptile and bird features, was an excellent example of Darwinian evolution.

Charles Doolittle Walcott & & & (1850 - 1927) in 1909 discovered 520-milion year old fossiliferous rocks high in the Canadian Rockies and opened one of the world's most famous 'windows' into the deep past. Known as the Burgess Shale, these ancient sea-bed sediments have yielded thousands of remarkably preserved fossils, many still with soft parts intact. They provide a vivid picture of life in Cambrian seas.

First described as an extinct group of primitive bony fish by Louis Agassiz in 1839 coelocanths were thought to have died out, but in 1938 one was caught off South Africa. Live examples were filmed in 1987, and a new population found in 1998 off Indonesia.

Elso Barghoorn & (1915 - 1984) in 1965 discovered precambrian microfossils in Canada, the earliest known, associated with laminated mound structures called stromatolites.


More About Evolution

Evidence Suporting Biological Evolution
Wikipedia on Evolution
Understanding Evolution Berkeley
US National Academy of Sciences
Becoming Human Palaeoanthropology
BBC Education - Darwin
US Public Broadcasting Service Introducing Evolution
Introducing Evolution
New Scientist: Articles on Evolution
Pharyngula: A Book List for Evolutionists

Walking Back to Genesis Dawkins on The Ancestor's Tale.
The World of Dawkins
Stephen Jay Gould Archive
J.D.Hooker (botanist)

Altruism in-built in humans (and chimps)
Mutations-DNA repair
Mitochondrial DNA and Human Evolution
Evolution and the Immune Response to Infection
Evolutionary News
RNA World
Evolutionary Neighbours, Primates
Self-replication: peptides
2004: New Clues to Human Evolution

Evolution of Horses
Shrewsbury Darwin festival
29+ Evidences for Evolution
Dating the Geological record
Darwin on line news
The Darwin project
Oldest Bee Fossil
Tiktaalik - the newly found "missing link"
The Imminent Demise of Evolution - historical survey
Great tits challenge evolutionary theory
Homosexuality in Animals - Oslo exhibition
Genetic Origins of Britons
"Lucy's daughter" - hominid fossil find
Antiquity of Man by Mikey Brass
Evolution Project
World Summit on Evolution 2005
lefalophodon - history of evolutionary biology
Human Palaeontology

For more links see countering creationism.

The Science Book edited by Peter Tallack has been a useful guide in the compilation of the information on this page.