Evolution of life?

What is evolution?

What are the main ideas of the following Scientists about the evolution of life?

AristotleLamarck DarwinMendelLysenko

Aristotle (384-322 BC)

• "Aristotelianism”– Partly based on Plato's world of

ideas– The species are given categories in

nature and are unchangeable– There are only variation in mature

and perfection of individuals– The only development is the mature

of each individual where the aim is to reach perfection which is given in the ideal types of the species

Aristotle’s epigenesis I.

• All living creatures, whether they swim, or walk, or fly, and whether they come into the world with the form of an animal or of an egg, are engendered in the same way.

• Concept of epigenesis and that in the embryo, more generalized structures appear before the more specialized ones.

• Epigenesis was one correct idea of Aristotle that was often discarded.

Aristotle’s epigenesis II.• His concepts of heredity were even sounder than

Darwin's (!) • Darwin believed in pangenesis (gemmules from all parts

of the body migrate to the semen and account for paternal characteristics).

• This was an old idea that Aristotle had refuted by fairly sound reasoning, among them:– children sometimes resemble distant relatives more than their

parents. This couldn't occur if the genetic particles were obtained by direct transmission.

– children of mutilated/crippled parents do not display these mutilations

– both male AND female contribute to the characteristics of the offspring.

Jean-Baptiste de Monet, chevalier de Lamarck

(1744-1829) • "Lamarckism“

– French enlightenment – Naturalist and pre-Darwinian

evolutionist – Studied fossils and invertebrates– Species change over time by adapting

to new environments– Parents pass their traits on to their

offspring– If an organ is used, it will become

stronger, and if it is not used, it will weaken and may disappear in future generations

– He postulated that acquired characters can be inherited by future generations

Charles Robert Darwin (1809-1882)

• “Natural selection" / "Darwinism“– By variation in the population there

is an adaption to the environment through a natural selection of acquired characters represented in the variation of the species

– Darwin's concepts of heredity were that gemmules from all parts of the body migrate to the semen and account for paternal characteristics

– Evolution purely mechanistic process

Gregor Mendel (1822-1884)

• “Mendelian genetics“– His principle of factorial

inheritance and the quantitative investigation of single characters have provided the basis for modern genetics. Recognition came many years after his death, when his key article, ‘Experiments with plant hybrids’ (1866), was discovered.

The major insights attributed to Mendel are often summarized in two "laws":

• Principle of Segregation: – observable traits are passed down to offspring

via (discrete, non-blending) particles, one from each parent.

• Principle of Independent Assortment:– the particles (later dubbed genes by

American geneticist T. H. Morgan) from each parent are equally likely to be passed down to offspring.

T. H. Morgan 1866-1945

• Through study of “Drosophila”• Made an elegant proof that the

chromosomes are indeed the bearers of the hereditary factors or genes as they are now known

Trofim Denisovich Lysenko (1898-1976)

• “Lysenkoism“– developed a doctrine, compounded of

Darwinism and the work of Michurin, that heredity can be changed by good husbandry.

– As director of the Institute of Genetics of the Soviet Academy of Sciences (1940–65), he declared the accepted Mendelian theory erroneous, and ruthlessly silenced any Soviet geneticists who opposed him.

– He was dismissed by Khrushchev in 1965, having gravely hampered scientific and agricultural progress in the USSR.

James Watson 1962- & Francis Crick 1916-2004

• Figured out the structure of deoxyribonucleic acid, DNA.

• And that structure — a "double helix" that can "unzip" to make copies of itself — confirmed suspicions that DNA carries life's hereditary information.

Discussion questions

1. What is evolution? Explain and exemplify!

2. Does evolution have an aim?

3. Does evolution have a purpose?

Modern view on evolution

• Our very best evidence indicates that, in reality, all species in this world have equal lengths of evolutionary history.

• The differences are the result of coincidence in the pathways evolutionary movement takes.

• Evolution is ultimately about diversity, not about progress and without purpose or aim