teachings of those in authority, notably the Church
Later, through the work of nineteenth-century British naturalists influenced by Enlightenment ideals, an alternative explanation to creationism emerged: the idea that new species arose from existing ones through a long and gradual process of transformation, known as evolution. Charles Darwin (1809–82) is best known for his theory of evolution by natural selection or, in other words, the view that competition for resources (the ‘struggle for survival’) is both unavoidable and ubiquitous in nature and is the driving force behind the continuous transformation of living forms.
evolution Any change across successive generations in the inherited characteristics of biological populations
Darwin’s theory of natural selection was one of many emerging ideas of the time that attempted to explain the diversity of animals and species found in the world. Alfred Russell Wallace (1823–1913), a naturalist working independently of Darwin at around the same time, developed a very similar theory. Both Darwin and Wallace presented their ideas to the public in 1858, which caused great controversy because they directly challenged prevailing religious explanations.
What is natural selection? Natural selection is a process whereby nature selects the forms most likely to survive and reproduce in a particular population. For natural selection to work, there needs to be inheritable (i.e., genetic) variation within populations – which there usually is – as well as competition for resources necessary for life, such as food and space. Those organisms that manage to get copies of their genes into future generations transmit characteristics that continue to evolve through the generations. Over time, the organisms that are less successful in passing on their genes, and are less suited to their surroundings, gradually die out, while the more successful organisms survive. This process changes according to the environment in which the species exist. Changes to the body that are acquired in the course of life, for example loss of a limb, do not get passed on.
natural selection The process in nature by which, according to Darwin’s theory of evolution, only the organisms best adapted to their environment tend to survive and transmit their genetic characteristics in increasing numbers to succeeding generations, while those less well adapted tend to be eliminated
Sexual selection In order to leave descendants, individuals must not only survive but also reproduce. As a supplement to the principle of natural selection, Charles Darwin developed the idea of sexual selection to attempt to explain the presence of characteristics of male animals, such as the elaborate tails of peacocks or men’s deep voices, claiming that these secondary sexual characteristics evolved not because they increase the survival prospects of individuals, but because females prefer to mate with individuals with those features. If this is the case, then those specific characteristics are more likely to be passed on to future generations.
In birds, for example, one form of sexual selection occurs when males compete for particular territories. A bird that manages to get the best location is more likely to be chosen as a mate. Geoffrey Miller (2000) develops Darwin’s ideas and argues that human culture arose through a process of sexual selection. He argues that there are many characteristics of human culture that are not necessary to survival yet play a strong role in sexual selection, for example humour. Miller believes that human culture arose through sexual selection for creative traits. In summary, since the main challenges faced by living beings are survival and reproduction, species are the outcome of both natural and sexual selection. Evolutionary anthropologists are still debating which features of humans were caused by natural selection and which were the result of sexual selection.
This peacock’s tail is an example of female preference driving the evolution of longer, more colourful tail feathers. (Taychin Olarnwichitwong / Unsplash)
STOP & THINK
Can you think of other traits that humans might look for in each other that are not necessary for survival?
After Darwin
Following Darwin’s contributions, the field of genetics emerged, which went into more detail in explaining biological variation. Gregor Mendel (1822–84) was a naturalist and a monk who made a series of original discoveries in the field of genetics that eventually provided support to Darwin’s theory of natural selection.
More recently, geologists have been able to divide the history of the Earth into specific periods or epochs. It is now generally agreed by scientists, archaeologists and anthropologists that the group of primates to which humans belong, known as hominins, first appeared 6–7 million years ago, with modern humans (Homo sapiens) appearing around 200,000 years ago. Paleoanthropology (the study of human fossil remains) and anthropological genetics (the comparative study of genes in humans and other species) have made significant progress in reconstructing the steps that led from our earliest ancestors to modern humans. Since the earliest forms of life date back to 4,000 million years ago, human beings are a relatively recent species in the history of life on planet Earth.
hominins Primates, species who are closely related to human beings or who are regarded as human
paleoanthropology The study of extinct early primates and fossil remains of early primates
Early humans
There were around twenty different species of early humans. While it was once thought that they existed separately, recent genetic evidence now suggests that there was significant overlap between early human groups. It is now understood that modern humans, on emerging first from Africa around 70,000 years ago, encountered and mated with Neanderthals in the Middle East. Children born from these encounters carried some Neanderthal genes, and, as modern humans advanced throughout Europe and Asia, they carried these genes with them. There have recently been a number of findings about the overlaps between early groups of humans. This section explores some of the most well-known recent examples that provide significant insights into the evolution of hominins.
Australopithecus afarensis : Lucy
Lucy was discovered in 1974 by anthropologist Professor Donald Johanson and his student Tom Gray, at Hadar in northern Ethiopia, and became one of the best documented of all early humans. Johanson and Gray named their fossil skeleton Lucy, after the Beatles song ‘Lucy in the Sky with Diamonds’, which was playing on the radio when the team was celebrating its discovery back at camp. The significance of this discovery was that it confirmed that bipedalism, the ability to walk on two legs, not four, was a key to what makes humans distinctive.
Johanson immediately recognized the bones as belonging to a hominid, and his team eventually unearthed forty-seven bones of a single skeleton dating from 3.2 million years ago. Based on the small size and pelvis shape, they concluded that the skeleton was that of a young female. Like a chimpanzee, Lucy had a small brain, long dangly arms and short legs. However, the structure of her knee and pelvis show that she usually walked upright on two legs.
Homo neanderthalensis
Together with early Asian people known as Denisovans, Neanderthals are our closest known ancient human
