What is evolution?
Evolution is, in essence, change over time. Evolution has given rise to every species we now know today and every species that has ever existed on this Earth. Most commonly, the term evolution will be used in reference to biological evolution, which refers to changes in populations resulting from natural selection acting over generations on inherited phenotypes, producing differential survival and reproduction under a particular set of environmental conditions.
Genes represent the segments of DNA that provide the chemical code for producing proteins. Information contained in the DNA can be altered by a process known as mutation, or through the process of recombination which occurs during sexual reproduction. The way particular genes are expressed is also subject to change. As genes control how the body and behaviour of an organism develop during its life, heritable characteristics can influence the likelihood of an organism’s survival and reproduction (i.e. genes for particular traits are capable of providing evolutionary advantages).
In tandem with these biological changes, there are also a number of behavioural changes which occur alongside the genetic changes of evolution, such as the development of language, or use of tools. Such cultural and technological changes bring about their own form of evolution, but ultimately it is the interplay of the three which over generations, has led to the development of the several extinct human species we know of today, as well as our own.
It is important to note that evolution does not change any single individual. Instead, it changes the inherited means of growth and development that typify a population (a group of individuals of the same species living in a particular habitat). Parents pass adaptive genetic changes to their offspring, and ultimately these changes become common throughout a population. As a result, the offspring inherit those genetic characteristics that enhance their chances of survival and ability to give birth, which may work well until the environment changes. Over time, genetic change can alter a species' overall way of life, such as what it eats, how it grows, and where it can live. Human evolution took place as new genetic variations in early ancestor populations favoured new abilities to adapt to environmental change and so altered the human way of life.
Evolution is, in essence, change over time. Evolution has given rise to every species we now know today and every species that has ever existed on this Earth. Most commonly, the term evolution will be used in reference to biological evolution, which refers to changes in populations resulting from natural selection acting over generations on inherited phenotypes, producing differential survival and reproduction under a particular set of environmental conditions.
Genes represent the segments of DNA that provide the chemical code for producing proteins. Information contained in the DNA can be altered by a process known as mutation, or through the process of recombination which occurs during sexual reproduction. The way particular genes are expressed is also subject to change. As genes control how the body and behaviour of an organism develop during its life, heritable characteristics can influence the likelihood of an organism’s survival and reproduction (i.e. genes for particular traits are capable of providing evolutionary advantages).
In tandem with these biological changes, there are also a number of behavioural changes which occur alongside the genetic changes of evolution, such as the development of language, or use of tools. Such cultural and technological changes bring about their own form of evolution, but ultimately it is the interplay of the three which over generations, has led to the development of the several extinct human species we know of today, as well as our own.
It is important to note that evolution does not change any single individual. Instead, it changes the inherited means of growth and development that typify a population (a group of individuals of the same species living in a particular habitat). Parents pass adaptive genetic changes to their offspring, and ultimately these changes become common throughout a population. As a result, the offspring inherit those genetic characteristics that enhance their chances of survival and ability to give birth, which may work well until the environment changes. Over time, genetic change can alter a species' overall way of life, such as what it eats, how it grows, and where it can live. Human evolution took place as new genetic variations in early ancestor populations favoured new abilities to adapt to environmental change and so altered the human way of life.
Human evolution
Human evolution is the lengthy process of change by which people (Homo sapiens) originated from apelike ancestors. Humans evolved over a period of approximately 6 million years, with the clear division of human lineage to the great ape lineage occurring around 4 million years ago. Scientists generally agree that that between 15 and 20 different species of early humans existed, however, there is still ongoing dispute on how these species are related, and which ones simply "died out." Two main theories for the evolution of modern-day humans exist; the multi-regional hypothesis and the "out of Africa" model. For the purposes of this website, we will base our information on the "out of Africa" model. According to this theory, humans first evolved in Africa, and much of human evolution occurred on this continent. The first species we consider to be part of human lineage are the Ardipithecus group, with the oldest fossil being dated to have lived somewhere between approximately 7 and 6 million years ago. They had mostly ape-like features, with sloping faces and very small brains (with the oldest species in this group, Sahelanthropus tchadensis, having a cranial capacity even smaller than that of a modern chimpanzee!) Although it is unknown if this group are direct ancestors of Homo sapiens, one of the key fossil characteristics which lead to their classification as early hominins is the indications of possible bipedalism. Following this were the Australopithecus group, which lived between approximately 4.2 and 2.1 million years ago. This group includes one of the most well-known and longest-lived species of early human Australopithecus afarensis, nicknamed "Lucy's species". Australopithecus had a mixture of ape-like and human-like features, with femur and foot bone fossils suggesting increased use of bipedalism as well as shoulder and arm bones that were well adapted for climbing. The next group which are generally identified as descendants of the Australopithecus group is the Paranthropus group, also referred to as robust Australopethicines. These early hominins lived approximately 2.7 to 1.2 million years ago, and are distinguished from the gracile Australopithecines (what we are referring to here as the Australopithecus group) by their larger brain case, strong muscles of mastication, and broad, grinding herbivorous teeth. Paranthropus co-existed alongside members of both the Australopithecus and Homo groups. The final genus in the evolutionary tree of humans is the Homo group. Like modern humans, members of the Homo group had large brains and used tools. They were also the first hominins to expand out of Africa, with the first migrations of early Homo species occurring between 2 million and 1.8 million years ago, during which time early Homo species reached East Asia. By approximately 1.5 million to 1 million years ago, they reached Europe. Later, Homo sapiens moved to Australia (~60,000-50,000 y.a) and the Americas (~15,000-12,000 y.a). While several Homo species existed, some prior to and some alongside Homo sapiens, it was our species which survived and has gone on to uncover all of this information about our lineage. |
Figure 2.1 A classic Darwinian depiction of evolution
NOTE: Although several linear depictions of human evolution exist, in reality human lineage consists of several different branches and pathways, not a linear path (see HOMINID FAMILY TREE link above) Figure 2.2 A representation of human evolution
Notable features of comparison include: brow ridge, slope of the face, cranial capacity, declination of the forehead, prominence of cheekbones, width of and appearance of jaw. Figure 2.3 Map of early human migration
Homo sapiens were the only Homo species to migrate beyond Africa, Asia and Europe. Figure 2.4 Millions of years of evolution... What has it led to?
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