The Effect of Competition On Speciation in the Human Lineage

Our species of humans — homo sapiens —are one of only about 20 discovered hominin species within our genus over our entire history. What is more, for the majority of our 300,000 years-or-so of our existence on this planet, we did not walk alone.

We shared this planet with at least six of our sibling species: the Neanderthals, Denisovans, Homo floresiensis (mainly Indonesia), Homo luzonensis (discovered in the Philippines), and Homo naledi (South Africa).

From what we know so far, it appears that each of these lineages trace back to a common hominin ancestor around 6 Mya. [1]

Climate Change, Competition, and Speciation

It was the previous consensus that climate change was the primary factor for the emergence and extinction of hominin species, however, new research — which found that the emergence of new species among humans is unparalleled — suggests that interspecies competition is a driving factor in our evolution. [1]

For other vertebrates, competition has been shown to generally supress speciation after an ecological niche is filled, but for the Homo lineage, increased competition has been shown to increase the rate of formation of new species. [1]

The evolutionary patterns of early hominins exemplified the familiar cycle. Species emerge rapidly when ecological competition is low. That species flourishes, and eventually plateaus and declines as the ecological niches are filled and competition intensifies. This is standard for vertebrate evolution. [1] However, species of the genus Homo defy this trend, with the rate of speciation increases the more species of our genus coexist at the same time. According to Dr. Laura van Holstein “[t]his is almost unparalleled in evolutionary science.” [1]

Understanding Hominin Speciation Through Fossils

In order to understand our story, we need more data. Over the past few decades several new hominin species have been discovered (such as Australopithecus and Homo floresensis).

Fossil record are our primary source for human prehistory. However, fossils are limited in that many factors limit the process of fossilization, thus what is fossilized — and the location of the fossil remains, the date, the physical characteristics, the quantity of remains — could be misleading.

The remains that do survive as fossils probably are not going to represent the birth of that species. It is also very speculative to attempt to extrapolate population numbers from scant fossils, or even their full geographical range in specific detail (aside from an island or continent, for example).

The process of fossilization is influenced by several factors such as geology and climate conditions. A hot, dry desert region will preserve remains better than a hot, humid, tropical environment, generally speaking. So there are some regions where it is simply unlikely for us to find remains, even if the region supported an extensive Homo population. Moreover, research is mostly concentrated in specific regions, thus many fossils varying by age and species remain undiscovered outside of those regions.

To combat these issues van Holstein employed data modelling (to factor in environmental conditions, their impact on fossilization, and other factors) in an attempt to work towards a better definition for population sizes, geographical ranges, and temporal boundaries for known hominin species. [1]

Findings challenged previous understanding that some species evolved through anagenesis — gradual evolution into another species without branching — suggesting they may have “budded” instead. Branching off from the parent population and developing into a new species, not unlike Roman Civilization growing from Ancient Greek Civilization.

It was once thought that Australophithecus afarensis evolved through anagenesis from Australopithecus anamensis. [1] However, new data suggests afarensis budded from anamensis, since they coexisted for around 500,000 years. [1]

The Impact of Technology on Evolution

Some researchers suggest that our intelligence — manifested in our ability to manufacture and use tools, fire, hunting techniques, etc. — increased our ability to adapt to new niches and so evolve more rapidly, without needing to evolve new physical traits first. [1]

Moreover, our capacity to think more abstractly enabled us to reason (to some degree) through problems presented by new environments, enabling us to occupy new ecological niches, and perhaps intensifying the rapid diversity of Homo species.

The result result of this process is us — Homo sapiens. It is likely that our success in adaptation enabled us to out-compete our sibling species, which led to their extinction.

Notes

Resources

References

1. Puiu, Tibit. How Our Human Lineage Broke All the Rules of Vertebrate Evolution. 24 Dec 2024. ZME Science. <https://www.zmescience.com/science/news-science/reverse-human-evolution/>. Accessed 02 Jan 2025.