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Human evolution was shaped by interspecies competition

A remarkable study led by researchers at the University of Cambridge proposes a dramatic shift in our understanding of human evolution. The research suggests that interspecies competition, rather than climate alone, significantly shaped the evolutionary trajectory of early humans.

Interspecies competition is a form of interaction where individuals of different species compete for the same resources in an ecosystem, such as food, space, or light. This type of competition can occur when resources are limited, leading to a struggle for survival among the competing species.

Climate vs. interspecies competition

Traditionally, researchers have viewed climate change as the primary driver of the emergence and extinction of hominin species. This view is consistent with the patterns observed in most vertebrates.

However, this new research indicates a crucial detail: for hominins – a group that includes modern humans and our extinct relatives – competition between species was a crucial factor. This competition significantly influenced our evolutionary history.

Minimal interspecies competition

The study reveals that over five million years, competition was fundamental to “speciation,” the emergence of new species in hominins.

“We have been ignoring the way competition between species has shaped our own evolutionary tree. The effect of climate on hominin species is only part of the story,” explained Dr. Laura van Holstein, a biological anthropologist at Clare College.

Using Bayesian modeling and phylogenetic analyses, van Holstein and her team demonstrated a key finding. Like in other vertebrates, most hominin species emerged when interspecies competition for resources was minimal.

This pattern, where speciation rates increase and then plateau before extinction rates rise, is consistent across many mammalian groups.

However, the evolutionary pattern of our own genus, Homo, is strikingly different. “The more species of Homo there were, the higher the rate of speciation,” noted Dr. van Holstein.

“This suggests that competition between species actually resulted in the appearance of even more new species – a complete reversal of the trend seen in almost all other vertebrates.”

This unique pattern of evolution in Homo is paralleled only by certain beetle species that inhabit islands. In these isolated ecosystems, unusual evolutionary trends can emerge.

“The patterns of evolution we see across species of Homo that led directly to modern humans is closer to those of island-dwelling beetles than other primates, or even any other mammal,” said Dr. van Holstein.

Fossil records and beyond

Dr. van Holstein created a new database which tracked each time an example of a species was found and dated in the hominin fossil record – including around 385 occurences.

This comprehensive data allowed the researchers to reconsider the start and end dates for most known hominin species, totaling 17.

Such an approach helps counteract the inherent limitations of fossil records. These records may not always capture the earliest or latest members of a species, due to geological and climatic factors affecting fossilization.

Interspecies competition, coexistence, and adaptation

Dr. van Holstein’s findings suggest a new perspective. Some species previously thought to have evolved through “anagenesis” may have actually “budded.” This indicates a branching off from an existing species rather than a linear evolution.

This realization implies a greater level of coexistence among hominin species. It also indicates heightened interspecies competition – more than previously acknowledged. Additionally, the study underscores the role of technology in the evolution of the genus Homo.

For example, early hominins like Paranthropus evolved physiologically to adapt, developing features like robust teeth. In contrast, Homo species adopted tools, fire, and intensive hunting techniques.

These advancements enabled the latter species to rapidly exploit new ecological niches, bypassing the need for significant physiological changes.

A legacy of interspecies competition

Ultimately, these findings underscore the complexity of interspecies competition, human evolution and the unique evolutionary path taken by our ancestors.

“These results show that, although it has been conventionally ignored, competition played an important role in human evolution overall,” said Dr. van Holstein. “Perhaps most interestingly, in our own genus it played a role unlike that across any other vertebrate lineage known so far.”

The study is published in the journal Nature Ecology & Evolution.


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