Tag Archives: multicellular

The Evolution of Sperm: Tracing Its Origins Before Multicellular Animals

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The origins of the sperm swimming mechanism date back to ancient times.

Christoph Burgstedt/Alamy

The evolutionary roots of sperm can be traced to the unicellular forerunners of all existing animals.

Nearly all animals go through a unicellular phase in their life cycle, which involves two forms of sex cells, or gametes. Eggs are sizeable cells that hold genetic information and the nutrients necessary for early development, while sperm transport genetic material from one organism to another to fertilize eggs and create new life.

“Sperms play a crucial role in the process that allows life to be transmitted from generation to generation,” states Arthur Matt from Cambridge University. “It carries the legacy of over 700 million years of evolutionary history and is likely linked to the origins of animals themselves. Our aim was to explore this extensive evolutionary narrative to understand the origins of sperm.”

Matt and his team utilized an open science dataset containing information about sperm proteins from 32 animal species, including humans. They combined this data with the genomes of 62 organisms, including various related single-cell groups, to track the evolution of sperm across different animal lineages.

The research revealed a “sperm toolkit” comprising about 300 gene families that make up the last universal common sperm core genome.


“We have now identified numerous significant advancements in sperm mechanisms occurring long before multicellular animals emerged, even before the sperm themselves,” explains Matt.

This indicates that the sperm mechanics, represented by a “flagellum that propels a single cell,” were already evolving prior to the development of multicellular organisms.

Thus, our ancient progenitors were once all single-celled oceanic swimmers, and the sperm toolkit was present in our earliest swimming unicellular predecessors long before the advent of animals.

“Animals evolved multicellularity and cellular differentiation, but they did not create sperm from nothing. They repurposed the body structure of their swimming forebears as the foundation for sperm,” states Matt. “In essence, sperm are not a novel creation of multicellular organisms but are constructed upon the designs of a single-celled organism repurposed for reproduction.”

The study also indicated that the significant technological developments leading to the vast variety of current sperm primarily affected the cell heads, while the tails have remained largely constant since their common ancestor.

According to the research team members, fertilization can occur in various manners, with some sperm reaching the egg within the body, while others swim in open waters, notes Adria Leboeuf, also from the University of Cambridge. “Finding eggs in these different settings presents unique challenges and requires specialized machinery,” she explains. “However, the tail remains well-preserved since it must be capable of swimming in all environments.”

“This illustrates how evolution can modify existing structures instead of creating mechanisms from scratch,” says Jenny Graves, from La Trobe University in Melbourne, Australia.

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Source: www.newscientist.com

Snowball Earth’s harsh environmental conditions provided a competitive edge for the evolution of multicellular organisms

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Fossil and molecular evidence suggests that complex multicellular organisms arose and proliferated during the Neoproterozoic Era (1-541 million years ago). An extreme glacial period during the Cryogenian Period (720-635 million years ago), an event commonly referred to as Snowball Earth, led to dramatic changes in Earth's climate and oceans. New research suggests that Snowball Earth was an environmental trigger for the proliferation of complex multicellularity across multiple groups of eukaryotic organisms.

Artist's impression of “Snowball Earth.” Image courtesy of NASA.

Solving the mystery of why multicellular organisms emerged could help pinpoint life on other planets and explain the enormous diversity and complexity seen on Earth today, from marine sponges to redwoods to human societies.

The prevailing thinking is that oxygen levels must reach a certain threshold for a single cell to form a multicellular colony.

However, the oxygen story does not fully explain why the multicellular ancestors of animals, plants and fungi emerged simultaneously, or why the transition to multicellularity took more than a billion years.

The new study shows how the specific physical conditions of Snowball Earth, particularly the viscosity of the oceans and the depletion of resources, may have led eukaryotes to become multicellular.

“It seems almost counterintuitive that these extremely harsh conditions – this frozen planet – could actually select for larger, more complex organisms, rather than causing species to become extinct or shrink in size,” said William Crockett, a doctoral student at MIT.

Using scaling theory, Crockett and his colleagues found that a hypothetical ancestor of early animals, reminiscent of swimming algae that fed on prey instead of photosynthesizing, would have grown in size and complexity under Snowball Earth pressures.

In contrast, single-celled organisms that move and feed by diffusion, such as bacteria, will grow small.

“The world changed after Snowball Earth because new life forms emerged on the planet,” said Professor Christopher Kemps of the Santa Fe Institute.

“One of the central questions of evolution is: How did we evolve from nothing on Earth to beings and societies like us? Was it all by chance?”

“We don't think it's luck. There are ways to predict these big changes.”

The study shows how, during the Snowball Earth era, the oceans froze, blocking sunlight and reducing photosynthesis, which resulted in nutrient depletion in the oceans.

Larger organisms that could process more water were more likely to eat enough to survive.

As the glaciers melt, these large creatures could expand even further.

“Our study provides hypotheses about ancestral features to look for in the fossil record,” Crockett said.

of study Published in Proceedings of the Royal Society B.

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William W. Crockett others2024. Snowball Earth's physical constraints drive the evolution of multicellularity. Proc. R. Soc. B 291 (2025): 20232767; doi: 10.1098/rspb.2023.2767

This article is a version of a press release provided by the Santa Fe Institute.

Source: www.sci.news