When he had heart surgery in 1983, he received blood infected with HIV. He developed AIDS, and died of the effects of the medical condition in 1992. His widow did not speak of this until years later.
November 13
1980
1980 (MCMLXXX) was .
1936
March 5
1963
1963 (MCMLXIII) is .
April 17
April 14
1977
1977 (MCMLXXVII) was .
March 24
May 12
1907
1907 (MCMVII) was a common year starting on Tuesday of the Gregorian calendar.
December 18
June 4
November 12
September 14
July 30
September 28
February 6
1911
1911 (MCMXI) was a common year starting on Sunday of the Gregorian calendar.
March 29
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May 19
February 24
1962
1962 (MCMLXII) was .
Evolution
Evolution is a biological process. It is how living things change over time and how new species develop. The theory of evolution explains how evolution works and how living and extinct things have come to be the way they are. The theory of evolution is a very important idea in biology. Theodosius Dobzhansky, a well-known evolutionary biologist, has said: "Nothing in biology makes sense except in the light of evolution".
Evolution has been happening since life started on Earth and is happening now. Evolution happens mostly by natural selection. Living things are all different from each other. Even living things of the same species look, move, and behave differently. Some differences make it easier for living things to survive and have babies. Differences may make it easier to find food, hide from danger, or have babies. The babies keep some of the differences that made it easier for their parents to have them. Over time, these differences get bigger and living things change enough to be a new species.
It is known that living things have changed over time, because their remains can be seen in the rocks. These remains are called 'fossils'. This proves that the animals and plants of today are different from those of long ago. The older the fossils, the bigger the differences from modern forms. This has happened because evolution has taken place. That evolution has taken place is a fact, because it is overwhelmingly supported by many lines of evidence. At the same time, evolutionary questions are still being actively researched by biologists.
Comparison of DNA sequences allows organisms to be grouped by how similar their sequences are. In 2010 an analysis compared sequences to phylogenetic trees, and supported the idea of common descent. There is now "strong quantitative support, by a formal test", for the unity of life.
The evidence for evolution is given in a number of books. Some of this evidence is discussed here.
The realization that some rocks contain fossils was a very important event in natural history. There are three parts to this story:
This is a topic which fascinated both Charles Darwin and Alfred Russel Wallace. When new species occur, usually by the splitting of older species, this takes place in one place in the world. Once it is established, a new species may spread to some places and not others.
Australasia has been separated from other continents for many millions of years. In the main part of the continent, Australia, 83% of mammals, 89% of reptiles, 90% of fish and insects and 93% of amphibians are endemic. Its native mammals are mostly marsupials like kangaroos, bandicoots, and quolls. By contrast, marsupials are today totally absent from Africa and form a small portion of the mammalian fauna of South America, where opossums, shrew opossums, and the monito del monte occur (see the Great American Interchange).
The only living representatives of primitive egg-laying mammals (monotremes) are the echidnas and the platypus. They are only found in Australasia, which includes Tasmania, New Guinea, and Kangaroo Island. These monotremes are totally absent in the rest of the world. On the other hand, Australia is missing many groups of placental mammals that are common on other continents (carnivora, artiodactyls, shrews, squirrels, lagomorphs), although it does have indigenous bats and rodents, which arrived later.
The evolutionary story is that placental mammals evolved in Eurasia, and wiped out the marsupials and monotremes wherever they spread. They did not reach Australasia until more recently. That is the simple reason why Australia has most of the world's marsupials and all the world's monotremes.
The evolution of the horse family (Equidae) is a good example of the way that evolution works. The oldest fossil of a horse is about 52 million years old. It was a small animal with five toes on the front feet and four on the hind feet. At that time, there were more forests in the world than today. This horse lived in woodland, eating leaves, nuts and fruit with its simple teeth. It was only about as big as a fox.
About 30 million years ago the world started to become cooler and drier. Forests shrank; grassland expanded, and horses changed. They ate grass, they grew larger, and they ran faster because they had to escape faster predators. Because grass wears teeth out, horses with longer-lasting teeth had an advantage.
For most of this long period of time, there were a number of horse types (genera). Now, however, only one genus exists: the modern horse, "Equus". It has teeth which grow all its life, hooves on single toes, great long legs for running, and the animal is big and strong enough to survive in the open plain. Horses lived in western Canada until 12,000 years ago, but all horses in North America became extinct about 11,000 years ago. The causes of this extinction are not yet clear. Climate change and over-hunting by humans are suggested.
So, scientists can see that changes have happened. They have happened slowly over a long time. How these changes have come about is explained by the theory of evolution.
In about , the Hawaiian Islands have the most diverse collection of "Drosophila" flies in the world, living from rainforests to mountain meadows. About 800 Hawaiian fruit fly species are known.
Genetic evidence shows that all the native fruit fly species in Hawaii have descended from "a single ancestral species" that came to the islands, about 20 million years ago. Later adaptive radiation was caused by a lack of competition and a wide variety of vacant niches. Although it would be possible for a single pregnant female to colonise an island, it is more likely to have been a group from the same species.
The combination of continental drift and evolution can explain what is found in the fossil record. "Glossopteris" is an extinct species of seed fern plants from the Permian period on the ancient supercontinent of Gondwana.
"Glossopteris" fossils are found in Permian strata in southeast South America, southeast Africa, all of Madagascar, northern India, all of Australia, all of New Zealand, and scattered on the southern and northern edges of Antarctica.
During the Permian, these continents were connected as Gondwana. This is known from magnetic striping in the rocks, other fossil distributions, and glacial scratches pointing away from the temperate climate of the South Pole during the Permian.
When biologists look at living things, they see that animals and plants belong to groups which have something in common. Charles Darwin explained that this followed naturally if "we admit the common parentage of allied forms, together with their modification through variation and natural selection".
For example, all insects are related. They share a basic body plan, whose development is controlled by master regulatory genes. They have six legs; they have hard parts on the outside of the body (an exoskeleton); they have eyes formed of many separate chambers, and so on. Biologists explain this with evolution. All insects are the descendants of a group of animals who lived a long time ago. They still keep the basic plan (six legs and so on) but the details change. They look different now because they changed in different ways: this is evolution.