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Portal:Evolutionary biology

The Evolutionary Biology Portal

Introduction

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Evolutionary biology is the subfield of biology that studies the evolutionary processes that produced the diversity of life on Earth, starting from a single common ancestor. These processes include natural selection, common descent, and speciation.

The discipline emerged through what Julian Huxley called the modern synthesis (of the 1930s) of understanding from several previously unrelated fields of biological research, including genetics, ecology, systematics, and paleontology.

Current research has widened to cover the genetic architecture of adaptation, molecular evolution, and the different forces that contribute to evolution including sexual selection, genetic drift, and biogeography. The newer field of evolutionary developmental biology ("evo-devo") investigates how embryonic development is controlled, thus creating a wider synthesis that integrates developmental biology with the fields covered by the earlier evolutionary synthesis.

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Species of the infraorder Cetacea

The evolution of cetaceans is thought to have begun in the Indian subcontinent, from even-toed ungulates 50 million years ago, over a period of at least 15 million years. Cetaceans are fully aquatic marine mammals belonging to the order Artiodactyla, and branched off from other artiodactyls around 50 mya (million years ago). Cetaceans are thought to have evolved during the Eocene or earlier, sharing a closest common ancestor with hippopotamuses. Being mammals, they surface to breathe air; they have 5 finger bones (even-toed) in their fins; they nurse their young; and, despite their fully aquatic life style, they retain many skeletal features from their terrestrial ancestors. Research conducted in the late 1970s in Pakistan revealed several stages in the transition of cetaceans from land to sea.

The two modern parvorders of cetaceans – Mysticeti (baleen whales) and Odontoceti (toothed whales) – are thought to have separated from each other around 28-33 million years ago in a second cetacean radiation, the first occurring with the archaeocetes. The adaptation of animal echolocation in toothed whales distinguishes them from fully aquatic archaeocetes and early baleen whales. The presence of baleen in baleen whales occurred gradually, with earlier varieties having very little baleen, and their size is linked to baleen dependence (and subsequent increase in filter feeding). Read more...

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Thylacine
Credit: Matilda

The last known Thylacine photographed at Hobart (formerly Beaumaris) Zoo in 1933. A scrotal sac is not visible in this or any other of the photos or film taken, leading to the supposition that "Benjamin" was a female, but the existence of a scrotal pouch in the Thylacine makes it impossible to be certain

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  • ...that adaptations enable living organisms to cope with environmental stresses and pressures?
  • ...that maintained gene flow between two populations can also lead to a combination of the two gene pools, reducing the genetic variation between the two groups?
  • ...that all forms of natural speciation have taken place over the course of evolution, though it still remains a subject of debate as to the relative importance of each mechanism in driving biodiversity?
  • ...that despite the relative rarity of suitable conditions for fossilization, approximately 250,000 fossil species are known?
  • ...that genetic sequence evidence thus allows inference and quantification of genetic relatedness between humans and other apes?

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