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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.

Convergent Evolution

Convergent Evolution

Evolution shapes the features of organisms over time, ensuring that they are suited for the environments in which they live. Sometimes, selection pressure leads to the rise of similar but unrelated adaptations in organisms with no recent common ancestors, a process known as convergent evolution.

What is Natural Selection?

What is Natural Selection?

Natural selection is an evolutionary process in which individuals with survival-promoting traits reproduce at higher rates. These favorable traits become more common within a population or species. Naturally selected traits initially arise via random genetic mutations. In order for selection to occur, there must be variation within a population, the trait controlling the variation must be heritable, and there must be an evolutionary advantage for variation in the trait.

Eukaryotic Evolution

Eukaryotic Evolution

The endosymbiont theory is the most widely accepted theory of eukaryotic evolution; however, its progression is still somewhat debated. According to the nucleus-first hypothesis, the ancestral prokaryote first evolved a membrane to enclose DNA and form the nucleus. Conversely, the mitochondria-first hypothesis suggests that the nucleus was formed after endosymbiosis of mitochondria.
Contrary to the endosymbiont theory, the eukaryote-first hypothesis proposes that the simpler prokaryotic and...

Synteny and Evolution

Synteny and Evolution

John H. Renwick first coined the term “synteny” in 1971, which refers to the genes present on the same chromosomes, even if they are not genetically linked. The species with common ancestry tend to show conserved syntenic regions. Therefore, the concept of synteny is nowadays used to describe the evolutionary relationship between species.
Around 80 million years ago, the human and mice lineages diverged from the common ancestor. During the course of evolution, the ancestral...

Position-effect Variegation

Position-effect Variegation

In 1928, a German botanist Emil Heitz observed the moss nuclei with a DNA binding dye. He observed that while some chromatin regions decondense and spread out in the interphase nucleus, others do not. He termed them euchromatin and heterochromatin, respectively. He proposed that the heterochromatin regions reflect a functionally inactive state of the genome. It was later confirmed that heterochromatin is transcriptionally repressed, and euchromatin is transcriptionally active chromatin.

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Related Experiment Video

Updated: Jan 20, 2026

A High-Throughput Enzyme-Coupled Activity Assay to Probe Small Molecule Interaction with the dNTPase SAMHD1

A High-Throughput Enzyme-Coupled Activity Assay to Probe Small Molecule Interaction with the dNTPase SAMHD1

Published on: April 16, 2021

Positive selection in dNTPase SAMHD1 throughout mammalian evolution.

Christopher Monit¹, Elizabeth R Morris², Christopher Ruis¹

¹Division of Infection and Immunity, University College London, WC1E 6BT London, United Kingdom.

Proceedings of the National Academy of Sciences of the United States of America

|August 28, 2019

Summary

This summary is machine-generated.

The protein SAMHD1, crucial for immunity and metabolism, shows signs of evolutionary adaptation across mammals. This suggests ongoing virus-host coevolution has shaped its antiviral functions.

Keywords:

HIV-1 SAMHD1 evolution mammals restriction

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Last Updated: Jan 20, 2026

A High-Throughput Enzyme-Coupled Activity Assay to Probe Small Molecule Interaction with the dNTPase SAMHD1

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Published on: April 16, 2021

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Examination of Thymic Positive and Negative Selection by Flow Cytometry

Published on: October 8, 2012

Area of Science:

* Molecular biology
* Evolutionary genetics
* Immunology

Background:

* SAMHD1 is a vertebrate protein with critical roles in cellular metabolism, antiviral defense, and innate immunity regulation.
* Its enzymatic activity lowers deoxynucleoside triphosphate levels, hindering viral replication.
* Primate lentiviruses have evolved countermeasures targeting SAMHD1, leading to observed coevolutionary adaptations in the host protein.

Purpose of the Study:

* To investigate the evolutionary history of SAMHD1 across mammalian lineages.
* To identify molecular signatures of coevolution between SAMHD1 and viral countermeasures.
* To understand how evolutionary pressures impact SAMHD1's diverse functions.

Main Methods:

* Analysis of SAMHD1 sequences from various mammalian lineages using codon-based likelihood models.
* Identification of sites under positive selection.
* Experimental validation of mutations' effects on SAMHD1's catalytic activity and antiviral function.

Main Results:

* Evidence of pervasive positive selection in SAMHD1 across multiple mammalian lineages.
* Positive selection identified at sites near T592, a key phosphorylation site regulating SAMHD1 activity.
* Experimental mutations in this cluster altered catalytic rate and lentiviral restriction capabilities.

Conclusions:

* Evolutionary signatures indicate SAMHD1 has undergone significant adaptation, likely driven by virus-host coevolution.
* Adaptations in SAMHD1's enzymatic function appear necessary to counteract viral evasion strategies.
* Ongoing positive selection may reflect a need to balance SAMHD1's antiviral, metabolic, and immune functions.