BIO 4113 – Evolutionary Biology Introduction

“….a beautifully simple and easily understood idea – evolution by natural selection – can be scientifically tested in all these fields. It is one of the most powerful ideas in all areas of science, and is the only theory that can seriously claim to unify biology.”

Evolution: change in living things by descent with modification.

The change may be range from DNA sequences to behavior.

Evolution depends on external environmental change and on random genetic changes. That means that the future course of evolution is unpredictable, unless we can specify future conditions.

Another aspect: evolution of life has proceeded in branching pattern, with the tremendous variety of modern species being descended from a common ancestor.

Adaptation – a critical concept.

Living things show adaptations.

Natural Selection: Simply put, some kinds of individuals in a population tend to contribute more offspring to the next generation than do others. Provided that the offspring resemble their parents, any attribute of an organism causing it to leave more offspring than average will increase in frequency in the population over time. The composition of the population will then change.

Some History

Maupertuis Darwin was not the first to question the idea that species were fixed, although it was certainly the commonly held belief at his time.

Diderot

The French naturalist Jean-Baptiste Lamarck put forward the idea that species changed over time in 1809 in his book

Philosphie Zoologique

. His process, though, was very different from that imagined by Darwin fifty years later. Lamarck suggested the idea of

transformism

. He

did not

suggest that lineages branched and went extinct.

Lamarck’s Theory actually had two parts: 1. Transformism 2. Inheritance of Acquired Characteristics.

Friction between Lamarck and the highly influential Georges Cuvier had a great influence on thinking through the early part of the 19 th Century.

Cuvier

Charles Darwin 1809-1882

Shrewsbury, England Charles Darwin was born on February 12, 1809, in Shrewsbury, England. Interestingly, another man was born on the same day in a log cabin in Kentucky. That man was Abraham Lincoln.

The Darwin family home was called “The Mount”. It was here that Darwin was born, and where his father practiced medicine.

Charles father, Robert Waring Darwin, was a prominent physician in Shrewsbury.

Erasmus Darwin (1731-1802 Organic life beneath the shoreless waves Was born and nurs’d in ocean’s pearly caves: First forms minute, unseen by spheric glass, Move on the mud, or pierce the watery mass; These, as successive generations bloom, New powers acquire and larger limbs assume; Whence countless groups of vegetation spring, And breathing realms of fin and feet and wing.

Shrewsbury School Charles was educated at home until the age of nine. He then attended Shrewsbury School, a boarding school located about a mile from his home, until he was sixteen.

In 1825, Charles entered the University of Edinburgh in Edinburgh, Scotland, to study to become a physician.

“The instruction at Edinburgh was altogether by lectures, and these were intolerably dull, with the exception of those on chemistry….to my mind there are few advantages and many disadvantages in lectures as compared with reading…. Dr. _____ made his lectures on human anatomy as dull as he was himself, and the subject disgusted me.”

Charles Darwin 1876

In 1827, Charles gave up the study of medicine and began studying for a career in the clergy at Christ’s College of Cambridge University.

During his time at Cambridge, Darwin was an “adequate” student, but busied himself with many other activities. He became fascinated with natural history. He was particularly fascinated with the intrigued by the enormous diversity of beetles.

Darwin was influenced by a Professor of Botany (and clergyman), John Stevens Henslow. Henslow persuaded Darwin to become interested in Geology.

“I fully believe a better man never walked this earth.”

Charles Darwin to Joseph Hooker regarding John Stevens Henslow.

John Henslow 1851

Henslow arranged for Darwin to accompany Adam Sedgwick on a field trip studying the geology of Wales in 1831. This stimulated Darwin’s interest in geology.

Adam Sedgewick

In 1831, Henslow arranged for Darwin to be interviewed for a position on board the HMS Beagle

Darwin was interviewed by Robert Fitzroy, and was offered a position as a “volunteer” naturalist on board the Beagle.

Captain Robert Fitzroy of the HMS Beagle

The Beagle sailed from Plymouth harbor on December 27, 1831.

The Beagle spent five years circumnavigating the globe.

South American sketch from Beagle voyage

The Beagle’s primary mission was mapping and exploring the coast of South America.

On the voyage, Darwin read Lyell’s Principles of Geology. It persuaded him that the earth was very ancient.

Charles Lyell Author of Principles of Geology

The Galapagos Darwin was particularly influenced by observations made in the Galapagos Islands, some 500 miles off the coast of Ecuador.

Pinnacle Rock The Galapagos are a group of volcanic islands, isolated from the South American mainland.

The islands are inhabited by a diverse group of organisms that differ from those found on the mainland.

Marine iguana

Darwin’s Finches

On his return, Darwin married his cousin Emma Wedgewood. They had ten children, with seven surviving to adulthood.

Charles with his daughter

In 1842, the Darwins moved to Down House in Kent, about sixteen miles from London. Darwin never left the British Isles again.

He spent much of his time in his study, working on his ideas.

Darwin’s microscope

Darwin became one of the world’s leading authorities on a wide range of topics, including barnacles…… …. and volcanic islands.

“ “I happened to read for amusement Malthus on Population and, being well prepared to appreciate the struggle for existence which everywhere goes on from long-continued observation of the habits of animals and plants, it at once struck me that under these circumstances favourable variations would tend to be preserved and unfavourable ones to be destroyed.”

Darwin, on reading Malthus’ Essay on the Principle of Population in 1838.

Thomas Malthus

In 1844, Darwin received a manuscript from Alfred Russell Wallace, a young naturalist who was working in the Malay Archipelago.

Darwin moved rapidly, and Origin of Species was published in 1859

The monumental new idea in Origin of Species was not the idea that species had evolved. The enormous step that Darwin took was the suggestion of a mechanism by which evolution could take place.

Darwin’s ideas were immediately controversial in the public eye, although most scientist’s were quickly convinced of the validity of his arguments.

One of the better arguments against Darwin’s theory was that it lacked a satisfactory theory of heredity. In fact, Darwin preferred a “blending” theory of inheritance. In truth, such a mechanism of inheritance would work against evolution by natural selection.

A more popular objection had to do with the role of chance, and the difficulty of making big jumps on the basis of chance and natural selection alone. A comparative anatomist named George Mivart published a book in 1871 in which he listed a number of structures that would be maladaptive in their early stages. Wing, for example.

Some biologists tried to get around the difficulty by thinking of a process other than natural selection that could work in the early stages of a new structure or organ. They fall in the area of “directed mutation”. The idea is that offspring tended to differ from their parents in a particular direction. In other words, early birds would tend to produce offspring with more developed wings, even though there was no advantage to it. Lamarckian.

In the 1880’s, Lamarckian inheritance was largely debunked through the experiments of August Weismann.

His work led to a rediscovery of the work of….

….Gregor Mendel.

Early on, the effect of Mendel’s work was to cast doubt on Darwin’s theory. The early Mendelian geneticists like Hugo de Vries and William Bateson opposed natural selection. They thought that evolution proceeded in big jumps powered by macromutations. Big difference between parent and offspring.

On the other hand, another school of geneticists called themselves biometricians. They were led by Karl Pearson. Biometricians looked at small differences between individuals instead of large. Source of much of biological statistics. Saw evolution as more of a statistical shift of the whole population instead of the production of an entirely new type of organism by macromutation. They tended to be more sympathetic to Darwin than the Mendelians.

The Modern Synthesis

Theodosius Dobzhansky immigrated from Russia in 1927 and began studies on evolution in fruit flies.

The question of how species originate was investigated by Ernst Mayr.

George Gaylord Simpson argued that the evidence in the fossil record was consistent with the population genetic mechanisms of the modern synthesis.

Stephen Jay Gould