History of Evolution

Year

Topic

Theoretical implications

1745

Maupertuis proposes an adaptationist account of organic design

Presupposes some mechanism for transmitting adaptations

1859

Darwin publishes The Origin of Species, vastly strengthening the adaptationist hypothesis

1865

Gregory Mendel publishes evidence for the discreteness and combinatorial rules of inherited traits

Traits are carried by discrete units, or genes; the results are not appreciated until 1900 

1869

Miescher discovers "nuclein" (DNA) in the cells from pus in open wounds -- cells composed mostly of nuclear material. It became known as nucleic acid after 1874, when Miescher separated it into a protein and an acid molecule. 

Suspected of exerting some function in the hereditary process

1918-1926

Muller formulates the chief principles of spontaneous gene mutation as point effects of ultramicroscopic physico-chemical accidents; he induces such changes using X-rays

The gene constitutes the basis of life and evolution by virtue of its property of reproducing its own internal changes

1920s

Nucleic acid found to be a major component of the chromosomes

Its molecular structure was thought to be simple, so  it was not a good candidate for a carrier of genetic information

1930s

Chemical nature of nuclei acid  investigated. It was thought to be a tetranucleotide composed of one unit each of adenylic, guanylic, thymidylic and cytidylic acids

The ubiquitous presence of nucleic acid in the chromosome was generally explained in purely physiological or structural terms

early 
1940s

The molecular weight of nucleic acid was found to be much higher than the tetranucleotide hypothesis required, but it was still viewed as a uniform polymer, like starch, unaffected by its biological source

Hereditary information was commonly thought to reside in the chromosomal proteins, since these differ across species, between individuals, and even within an organism

1944

Oswald Avery identifies nucleic acids as the active principle in bacterial transformation

 "If the results of the present study of the transforming principle are confirmed, then nucleic acids must be regarded as possessing biological specificity the chemical basis of which is as yet undetermined."

1950

Erwin Chargaff shows that the four nucleotides are not present in nucleic acids in stable proportions, and that the nucleotide composition differs according to its biological source.

The nucleic acids are not monotonous polymers.

1952

Alfred Hershey and Martha Chase show that on infection of the host bacterium by a virus, at least 80% of the viral DNA enters the cell and at least 80% of the viral protein remains outside.

DNA rather than proteins carry genetic information.

1953

Watson and Crick determine that deoxyribonucleic acid (DNA) is a double-strand helix of nucleotides. Each nucleotide consists of a deoxyribose sugar molecule to which is attached a phosphate group and one of four nitrogenous bases: two purines (A- adenine and G- guanine) and two pyrimidines (C- cytosine and T- thymine). The nucleotides are joined together by covalent bonds between the phosphate of one nucleotide and the sugar of the next, forming a phosphate-sugar backbone from which the nitrogenous bases protrude. The two strands are linked by selective hydrogen bonds: the purine adenine bonds only with the pyrimidine thymine, and the purine cytosine only with the pyrimidine guanine.

DNA replication is possible through the complementary nature of the two strands. The chemical complexity of the molecule is thought to be sufficient to store the requisite information. 

The precise manner in which the information in the DNA is activated to build an organism is still very poorly understood; what is firmly demonstrated is that so-called structural genes manufacture the proteins for living tissues.

Early 1970s

Comparisons between chimpanzee and human genomes finds that they diverge by only 1.6%--less than most sibling species, which barely differ in morphology, and far less than that between any pair of congeneric species (Wilson 1975: 113)

The theoretical implications are unclear; morphological and behavioral differences between the two species appeared to be unaccounted for by the genetic material (cf. Cherry et al, 1978; for an update, see <a href="http://cogweb.ucla.edu/Abstracts/Gibbons_98.html"> Gibbons 1998</a>).

Early 1970s

The discovery of regulator genes--genes that control the timing and output of structural genes

Since a regulator gene may control thousands of structural genes, and indeed other regulator genes, the logical inference is that human and chimpanzee genomes are being switched on and off in quite different ways (King and Wilson 1975)

1980s

McClintock discovered transposable strands of genes in maize already in the 1940s, but her work was not fully recognized for a generation.

The genome may be controlling aspects of its own mutation (see Pennisi 1998 and Chicurel 2001 for an overview). 

1984

McGinnis discovers homeotic (Hox) regulatory genes, responsible for the basic body plan of most animals. In subsequent work, his team demonstrates that a single mutation in a Hox gene suffices to suppress all limb development in the thoracic region of fruit flies.

Macroevolutionary transitions, such as that from arthropods to hexapods (insects), may be initiated by point changes in regulatory genes.

2000

The Human Genome Project presents its preliminary results: each of the body's 100 trillion cells contains some 3.1 billion nucleotide units. Only 1% of these are thought to be transcriptional, clustered in possibly as few as 30,000 genes.

An accurate chemical map of the genome tells us surprisingly little about how it functions. Targeted experimentation is now possible.