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The Evidence for Evolution

The Evidence for Evolution

Genetic variations accumulating within populations over generations give rise to biological evolution. Evolutionary changes can result in the formation of novel varieties and entire new species. These changes are responsible for the diverse forms of life inhabiting the planet. The evidence for evolution suggests that all living organisms descended from common ancestors.The collection of fossils within sedimentary rocks give a record of common ancestry and often depicts the history of evolution.

Speciation Rates

Speciation Rates

Speciation can proceed at markedly different rates, and evolutionary biologists commonly describe these differences through the models of gradualism and punctuated equilibrium. Both patterns explain how new species arise, but they differ in the tempo and continuity of evolutionary change. In both cases, evolutionary change arises from heritable variation within populations, with natural selection often shaping traits that improve survival and reproduction under specific environmental conditions.

Genetics of Speciation

Genetics of Speciation

Speciation is the evolutionary process resulting in the formation of new, distinct species—groups of reproductively isolated populations.The genetics of speciation involves the different traits or isolating mechanisms preventing gene exchange, leading to reproductive isolation. Reproductive isolation can be due to reproductive barriers that have effects either before or after the formation of a zygote. Pre-zygotic mechanisms prevent fertilization from occurring, and post-zygotic mechanisms...

Gene Flow

Gene Flow

Gene flow is the transfer of genes among populations, resulting from either the dispersal of gametes or from the migration of individuals.

Formation of Species

Formation of Species

Speciation describes the formation of one or more new species from one or sometimes multiple original species. The resulting species are discrete from the parent species, and barriers to reproduction will typically exist. There are two primary mechanisms, speciation with and without geographic isolation—allopatric and sympatric speciation, respectively.Allopatric SpeciationIn allopatric speciation, gene flow between two populations of the same species is prevented by a geographic barrier, like...

What is Evolutionary History?

What is Evolutionary History?

Scientists record evolutionary history by analyzing fossil, morphological, and genetic data. The fossil record documents the history of life on Earth and provides evidence for evolution. However, both fossil and living organisms offer evidence that outlines Earth’s evolutionary history.Phylogenetic trees illustrate the evolutionary relationships among these organisms. Scientists infer organisms’ common ancestry by evaluating shared morphological and genetic characteristics. Together, the fossil...

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Updated: Jul 16, 2026

Resurrection of Dormant Daphnia magna: Protocol and Applications

Resurrection of Dormant Daphnia magna: Protocol and Applications

Published on: January 19, 2018

Evolution and the latitudinal diversity gradient: speciation, extinction and biogeography.

Gary G Mittelbach¹, Douglas W Schemske, Howard V Cornell

¹W.K. Kellogg Biological Station and Department of Zoology, Michigan State University, Hickory Corners, MI 49060, USA. mittelbach@kbs.msu.edu

Ecology Letters

|March 16, 2007

Summary

The long-standing biodiversity gradient from poles to equator is not fully explained. Two main hypotheses, time/area and diversification rates, offer insights into the origins of this global pattern.

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Area of Science:

Ecology and Evolutionary Biology
Biodiversity Science

Background:

A significant latitudinal gradient in biodiversity, with higher diversity in the tropics, has been recognized for a long time.
The precise mechanisms driving this gradient remain a subject of scientific inquiry.

Purpose of the Study:

To review and synthesize the major hypotheses explaining the origin of the latitudinal diversity gradient.
To evaluate the supporting evidence for competing hypotheses regarding biodiversity patterns.

Main Methods:

Literature review of ecological, evolutionary, and paleontological studies.
Analysis of phylogenetic and palaeontological data related to species origination and extinction rates.
Examination of studies on speciation rates across different latitudes.

Main Results:

The time and area hypothesis suggests older, larger tropical regions promote greater diversification.
The diversification rate hypothesis posits faster speciation or lower extinction in the tropics.
Evidence supports faster tropical speciation and origination, but extinction rate differences are less clear.

Conclusions:

Both historical factors (time and area) and ecological factors (diversification rates) likely contribute to the latitudinal diversity gradient.
Further research is needed to disentangle the relative importance of history, speciation, and extinction in shaping this pattern.