For several decades, critiques cast serious doubt on group selection as a major mechanism of evolution.
In simple cases it can be seen at once that traditional selection suffices. For example, if one sibling sacrifices itself for three siblings, the genetic disposition for the act will be increased. This is because siblings share on average 50% of their genetic inheritance, and the sacrificial act has led to greater representation of the genes in the next generation.
Altruism is now generally seen as emerging from standard selection. The warning note from Ernst Mayr, and the work of William Hamilton are both important to this discussion.
Hamilton's equation describes whether or not a gene for altruistic behaviour will spread in a population. The gene will spread if rxb is greater than c:
where:
At first, sexual reproduction might seem to be at a disadvantage compared with asexual reproduction. In order to be advantageous, sexual reproduction (cross-fertilisation) has to overcome a two-fold disadvantage (takes two to reproduce) plus the difficulty of finding a mate. Why, then, is sex so nearly universal among eukaryotes? This is one of the oldest questions in biology.
The answer has been given since Darwin's time: because the sexual populations adapt better to changing circumstances. A recent laboratory experiment suggests this is indeed the correct explanation.
In the main experiment, nematode worms were divided into two groups. One group was entirely outcrossing, the other was entirely selfing. The groups were subjected to a rugged terrain and repeatedly subjected to a mutagen. After 50 generations, the selfing population showed a substantial decline in fitness (= survival), whereas the outcrossing population showed no decline. This is one of a number of studies that show sexuality to have real advantages over non-sexual types of reproduction.
An important activity is artificial selection for domestication. This is when people choose which animals to breed from, based on their traits. Humans have used this for thousands of years to domesticate plants and animals.
More recently, it has become possible to use genetic engineering. New techniques such as 'gene targeting' are now available. The purpose of this is to insert new genes or knock out old genes from the genome of a plant or animal. A number of Nobel Prizes have already been awarded for this work.
However, the real purpose of studying evolution is to explain and help our understanding of biology. After all, it is the first good explanation of how living things came to be the way they are. That is a big achievement. The practical things come mostly from genetics, the science started by Gregor Mendel, and from molecular and cell biology.
In 2010 the journal "Nature" selected 15 topics as 'Evolution gems'. These were:
The idea that all life evolved had been proposed before Charles Darwin published "On the Origin of species". Even today, some people still discuss the concept of evolution and what it means to them, their philosophy, and their religion. Evolution does explain some things about our human nature. People also talk about the social implications of evolution, for example in sociobiology.
Some people have the religious belief that life on Earth was created by a god. In order to fit in the idea of evolution with that belief, people have used ideas like "guided evolution" or "theistic evolution". They say that evolution is real, but is being guided in some way.
There are many different concepts of "theistic evolution". Many creationists believe that the creation myth found in their religion goes against the idea of evolution. As Darwin realised, the most controversial part of the evolutionary thought is what it means for human origins.
In some countries, especially in the United States, there is tension between people who accept the idea of evolution and those who do not accept it. The debate is mostly about whether evolution should be taught in schools, and in what way this should be done.
Other fields, like cosmology and earth science also do not match with the original writings of many religious texts. These ideas were once also fiercely opposed. Death for heresy was threatened to those who wrote against the idea that Earth was the center of the universe.
Evolutionary biology is a more recent idea. Certain religious groups oppose the idea of evolution more than other religious groups do. For instance, the Roman Catholic Church now has the following position on evolution: Pope Pius XII said in his encyclical "Humani Generis" published in the 1950s:
Pope John Paul II updated this position in 1996. He said that Evolution was "more than a hypothesis":
The Anglican Communion also does not oppose the scientific account of evolution.
Many of those who accepted evolution were not much interested in biology. They were interested in using the theory to support their own ideas on society.
Some people have tried to use evolution to support racism. People wanting to justify racism claimed that certain groups, such as black people, were inferior. In nature, some animals do "survive" better than others, and it does lead to animals better adapted to their circumstances. With humans groups from different parts of the world, all evolution can say is that each group is probably well suited to its original situation. Evolution makes no judgements about better or worse. It does "not" say that any human group is superior to any other.
The idea of eugenics was rather different. Two things had been noticed as far back as the 18th century. One was the great success of farmers in breeding cattle and crop plants. They did this by selecting which animals or plants would produce the next generation (artificial selection). The other observation was that lower class people had more children than upper-class people. If (and it's a big if) the higher classes were there on "merit", then their lack of children was the exact reverse of what should be happening. Faster breeding in the lower classes would lead to the society getting worse.
The idea to improve the human species by selective breeding is called eugenics. The name was proposed by Francis Galton, a bright scientist who meant to do good. He said that the human stock (gene pool) should be improved by selective breeding policies. This would mean that those who were considered "good stock" would receive a reward if they reproduced. However, other people suggested that those considered "bad stock" would need to undergo compulsory sterilization, prenatal testing and birth control. The German Nazi government (1933–1945) used eugenics as a cover for their extreme racial policies, with dreadful results.
The problem with Galton's idea is how to decide which features to select. There are so many different skills people could have, you could not agree who was "good stock" and who was "bad stock". There was rather more agreement on who should "not" be breeding. Several countries passed laws for the compulsory sterilisation of unwelcome groups. Most of these laws were passed between 1900 and 1940. After World War II, disgust at what the Nazis had done squashed any more attempts at eugenics.
Some equations can be solved using algorithms that simulate evolution. Evolutionary algorithms work like that.
Another example of using ideas about evolution to support social action is social darwinism. Social darwinism is a term given to the ideas of the 19th century social philosopher Herbert Spencer. Spencer believed the "survival of the fittest" could and should be applied to commerce and human societies as a whole.
Again, some people used these ideas to claim that racism, and ruthless economic policies were justified. Today, most biologists and philosophers say that the theory of evolution should not be applied to social policy.