̽��ֱ�� of Cambridge - hominin

Interspecies competition led to even more forms of ancient human – defying evolutionary trends in vertebrates

fpjl2 — Wed, 17 Apr 2024 08:06:16 +0000

Climate has long been held responsible for the emergence and extinction of hominin species. In most vertebrates, however, interspecies competition is known to play an important role.

Now, research shows for the first time that competition was fundamental to 'speciation' – the rate at which new species emerge – across five million years of hominin evolution.

̽��ֱ��study, published today in Nature Ecology & Evolution, also suggests that the species formation pattern of our own lineage was closer to island-dwelling beetles than other mammals.

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

In other vertebrates, species form to fill ecological “niches” says van Holstein. Take Darwin’s finches: some evolved large beaks for nut-cracking, while others evolved small beaks for feeding on certain insects. When each resource niche gets filled, competition kicks in, so no new finches emerge and extinctions take over.

Van Holstein used Bayesian modelling and phylogenetic analyses to show that, like other vertebrates, most hominin species formed when competition for resources or space were low.

“ ̽��ֱ��pattern we see across many early hominins is similar to all other mammals. Speciation rates increase and then flatline, at which point extinction rates start to increase. This suggests that interspecies competition was a major evolutionary factor.”

However, when van Holstein analysed our own group, Homo, the findings were 'bizarre'.

For the Homo lineage that led to modern humans, evolutionary patterns suggest 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.

“ ̽��ֱ��more species of Homo there were, the higher the rate of speciation. So when those niches got filled, something drove even more species to emerge. This is almost unparalleled in evolutionary science.”

̽��ֱ��closest comparison she could find was in beetle species that live on islands, where contained ecosystems can produce unusual evolutionary trends.

“ ̽��ֱ��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.”

Recent decades have seen the discovery of several new hominin species, from Australopithecus sediba to Homo floresiensis. Van Holstein created a new database of 'occurrences' in the hominin fossil record: each time an example of a species was found and dated, around 385 in total.

Fossils can be an unreliable measure of species’ lifetimes. “ ̽��ֱ��earliest fossil we find will not be the earliest members of a species,” said van Holstein.

“How well an organism fossilises depends on geology, and on climatic conditions: whether it is hot or dry or damp. With research efforts concentrated in certain parts of the world, and we might well have missed younger or older fossils of a species as a result.”

Van Holstein used data modelling to address this problem, and factor in likely numbers of each species at the beginning and end of their existence, as well as environmental factors on fossilisation, to generate new start and end dates for most known hominin species (17 in total).

She found that some species thought to have evolved through 'anagenesis' – when one slowly turns into another, but lineage doesn’t split – may have actually 'budded': when a new species branches off from an existing one.

For example, the hominin species Australopithecus afarensis was believed to have speciated via anagenesis from Australopithecus anamensis. However, the new data modelling suggests they overlapped by around half a million years.

This meant that several more hominin species than previously assumed were co-existing, and so possibly competing.

While early species of hominins, such as Paranthropus, probably evolved physiologically to expand their niche – adapting teeth to exploit new types of food, for example – the driver of the very different pattern in our own genus Homo may well have been technology.

“Adoption of stone tools or fire, or intensive hunting techniques, are extremely flexible behaviours. A species that can harness them can quickly carve out new niches, and doesn’t have to survive vast tracts of time while evolving new body plans,” said van Holstein

She argues that an ability to use technology to generalise, and rapidly go beyond ecological niches that force other species to compete for habitat and resources, may be behind the exponential increase in the number of Homo species detected by the latest study.

But it also led to Homo sapiens – the ultimate generalisers. And competition with an extremely flexible generalist in almost every ecological niche may be what contributed to the extinction of all other Homo species.

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

Competition between species played a major role in the rise and fall of hominins, and produced a “bizarre” evolutionary pattern for the Homo lineage.

This is almost unparalleled in evolutionary science

Laura van Holstein

̽��ֱ��Duckworth Laboratory

A cast of the skull of Homo Heidelbergensis, one of the hominin species analysed in the latest study.

̽��ֱ��text in this work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License. Images, including our videos, are Copyright © ̽��ֱ�� of Cambridge and licensors/contributors as identified. All rights reserved. We make our image and video content available in a number of ways – on our main website under its Terms and conditions, and on a range of channels including social media that permit your use and sharing of our content under their respective Terms.

Yes

First hominin muscle reconstruction shows 3.2 million-year-old ‘Lucy’ could stand as erect as we can

fpjl2 — Wed, 14 Jun 2023 05:44:09 +0000

A Cambridge ̽��ֱ�� researcher has digitally reconstructed the missing soft tissue of an early human ancestor – or hominin – for the first time, revealing a capability to stand as erect as we do today.

Dr Ashleigh Wiseman has 3D-modelled the leg and pelvis muscles of the hominin Australopithecus afarensis using scans of ‘Lucy’: the famous fossil specimen discovered in Ethiopia in the mid-1970s.

Australopithecus afarensis was an early human species that lived in East Africa over three million years ago. Shorter than us, with an ape-like face and smaller brain, but able to walk on two legs, it adapted to both tree and savannah dwelling – helping the species survive for almost a million years.

Named for the Beatles classic ‘Lucy in the Sky with Diamonds’, Lucy is one of the most complete examples to be unearthed of any type of Australopithecus – with 40% of her skeleton recovered.

Wiseman was able to use recently published open source data on the Lucy fossil to create a digital model of the 3.2 million-year-old hominin’s lower body muscle structure. ̽��ֱ��study is published in the journal Royal Society Open Science.

̽��ֱ��research recreated 36 muscles in each leg, most of which were much larger in Lucy and occupied greater space in the legs compared to modern humans.

For example, major muscles in Lucy’s calves and thighs were over twice the size of those in modern humans, as we have a much higher fat to muscle ratio. Muscles made up 74% of the total mass in Lucy’s thigh, compared to just 50% in humans.

Paleoanthropologists agree that Lucy was bipedal, but disagree on how she walked. Some have argued that she moved in a crouching waddle, similar to chimpanzees – our common ancestor – when they walk on two legs. Others believe that her movement was closer to our own upright bipedalism.

Research in the last 20 years have seen a consensus begin to emerge for fully erect walking, and Wiseman’s work adds further weight to this. Lucy’s knee extensor muscles, and the leverage they would allow, confirm an ability to straighten the knee joints as much as a healthy person can today.

“Lucy’s ability to walk upright can only be known by reconstructing the path and space that a muscle occupies within the body,” said Wiseman, from Cambridge ̽��ֱ��’s McDonald Institute for Archaeological Research.

“We are now the only animal that can stand upright with straight knees. Lucy’s muscles suggest that she was as proficient at bipedalism as we are, while possibly also being at home in the trees. Lucy likely walked and moved in a way that we do not see in any living species today,” Wiseman said.

“Australopithecus afarensis would have roamed areas of open wooded grassland as well as more dense forests in East Africa around 3 to 4 million years ago. These reconstructions of Lucy’s muscles suggest that she would have been able to exploit both habitats effectively.”

Lucy was a young adult, who stood at just over one metre tall and probably weighed around 28kg. Lucy’s brain would have been roughly a third of the size of ours.

To recreate the muscles of this hominin, Wiseman started with some living humans. Using MRI and CT scans of the muscle and bone structures of a modern woman and man, she was able to map the “muscle paths” and build a digital musculoskeletal model.

Wiseman then used existing virtual models of Lucy’s skeleton to 'rearticulate' the joints – that is, put the skeleton back together. This work defined the axis from which each joint was able to move and rotate, replicating how they moved during life.

Finally, muscles were layered on top, based on pathways from modern human muscle maps, as well as what little “muscle scarring” was discernible (the traces of muscle connection detectable on the fossilised bones). “Without open access science, this research would not have been possible,” said Wiseman.

These reconstructions can now help scientists understand how this human ancestor walked. “Muscle reconstructions have already been used to gauge running speeds of a T-Rex, for example,” said Wiseman. “By applying similar techniques to ancestral humans, we want to reveal the spectrum of physical movement that propelled our evolution – including those capabilities we have lost.”

Reference:
Ashleigh L. A. Wiseman. 'Three-dimensional volumetric muscle reconstruction of the Australopithecus afarensis pelvis and limb, with estimations of limb leverage.' Royal Society Open Science (2023). DOI: 10.1098/rsos.230356

Digital modelling of legendary fossil’s soft tissue suggests Australopithecus afarensis had powerful leg and pelvic muscles suited to tree dwelling, but knee muscles that allowed fully erect walking.

Lucy’s muscles suggest that she was as proficient at bipedalism as we are

Dr Ashleigh Wiseman

A cross-section of the polygonal muscle modelling approach, guided by muscle scarring and MRI data.

̽��ֱ��text in this work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License. Images, including our videos, are Copyright © ̽��ֱ�� of Cambridge and licensors/contributors as identified. All rights reserved. We make our image and video content available in a number of ways – as here, on our main website under its Terms and conditions, and on a range of channels including social media that permit your use and sharing of our content under their respective Terms.

Yes

Height and weight evolved at different speeds in the bodies of our ancestors

fpjl2 — Wed, 08 Nov 2017 00:33:01 +0000

A wide-ranging new study of fossils spanning over four million years suggests that stature and body mass advanced at different speeds during the evolution of hominins – the ancestral lineage of which Homo sapiens alone still exist.

Published today in the journal Royal Society: Open Science, the research also shows that, rather than steadily increasing in size, hominin bodies evolved in “pulse and stasis” fluctuations, with some lineages even shrinking.

̽��ֱ��findings are from the largest study of hominin body sizes, involving 311 specimens dating from earliest upright species of 4.4m years ago right through to the modern humans that followed the last ice age.

While researchers describe the physical evolution of assorted hominin species as a “long and winding road with many branches and dead ends”, they say that broad patterns in the data suggest bursts of growth at key stages, followed by plateaus where little changed for many millennia.

̽��ֱ��scientists were surprised to find a “decoupling” of bulk and stature around one and a half million years ago, when hominins grew roughly 10cm taller but would not consistently gain any heft for a further million years, with an average increase of 10-15kgs occurring around 500,000 years ago.

Before this event, height and weight in hominin species appeared to evolve roughly “in concert”, say the authors of this first study to jointly analyse both aspects of body size over millions of years.

“An increase solely in stature would have created a leaner physique, with long legs and narrow hips and shoulders. This may have been an adaptation to new environments and endurance hunting, as early Homo species left the forests and moved on to more arid African savannahs,” says lead author Dr Manuel Will from Cambridge’s Department of Archaeology, and a Research Fellow at Gonville & Caius College.

“ ̽��ֱ��higher surface-to-volume ratio of a tall, slender body would be an advantage when stalking animals for hours in the dry heat, as a larger skin area increases the capacity for the evaporation of sweat.

“ ̽��ֱ��later addition of body mass coincides with ever-increasing migrations into higher latitudes, where a bulkier body would be better suited for thermoregulation in colder Eurasian climates,” he says.

However, Dr Will points out that, while these are valid theories, vast gaps in the fossil record continue to mask absolute truths. In fact, Will and colleagues often had to estimate body sizes from highly fragmented remains – in some cases from just a single toe bone.

̽��ֱ��study found body size to be highly variable during earlier hominin history, with a range of differently shaped species: from broad, gorilla-like Paranthropus to the more wiry or ‘gracile’ Australopithecus afarensis. Hominins from four million years ago weighed a rough average of 25kg and stood at 125-130cm.

As physicality morphs over deep time, increasingly converging on larger body sizes, the scientists observe three key “pulses” of significant change.

̽��ֱ��first occurs with the dawn of our own defined species bracket, Homo, around 2.2-1.9m years ago. This period sees a joint surge in both height (around 20 cm) and weight (between 15-20kg).

Stature then separated from heft with a height increase alone of 10cm between 1.4-1.6m years ago, shortly after the emergence of Homo erectus. “From a modern perspective this is where we see a familiar stature reached and maintained. Body mass, however, is still some way off,” explains Will.

It’s not until a million years later (0.5-0.4m years ago) that consistently heavier hominins appear in the fossil record, with an estimated 10-15kg greater body mass signalling adaptation to environments north of the Mediterranean.

“From then onwards, average body height and weight stays more or less the same in the hominin lineage, leading ultimately to ourselves,” says Will.

There are, however, a couple of exceptions to this grand narrative: Homo naledi and Homo floresiensis. Recently discovered remains suggest these species swam against the tide of increasing body size through time.

“They may have derived from much older small-bodied ancestors, or adapted to evolutionary pressures occurring in small and isolated populations,” says Will. Floresiensis was discovered on an Indonesian island.

“Our study shows that, other than these two species, hominins that appear after 1.4m years ago are all larger than 140cm and 40kg. This doesn’t change until human bodies diversify again in just the last few thousand years.”

“These findings suggest extremely strong selective pressures against small body sizes which shifted the evolutionary spectrum towards the larger bodies we have today.”

Will and colleagues say evolutionary pressures that may have contributed include ‘cladogenesis’: the splitting of a lineage, with one line – the smaller-bodied one, in this case – becoming extinct, perhaps as a result of inter-species competition.

They also suggest that sexual dimorphism – the physical distinction between genders, with females typically smaller in mammals – was more prevalent in early hominin species but then steadily ironed out by evolution.

Study co-author Dr Jay Stock, also from Cambridge’s Department of Archaeology, suggests this growth trajectory may continue.

“Many human groups have continued to get taller over just the past century. With improved nutrition and healthcare, average statures will likely continue to rise in the near future. However, there is certainly a ceiling set by our genes, which define our maximum potential for growth," Stock says.

“Body size is one of the most important determinants of the biology of every organism on the planet,” adds Will. “Reconstructing the evolutionary history of body size has the potential to provide us with insights into the development of locomotion, brain complexity, feeding strategies, even social life.”

̽��ֱ��largest study to date of body sizes over millions of years finds a “pulse and stasis” pattern to hominin evolution, with surges of growth in stature and bulk occurring at different times. At one stage, our ancestors got taller around a million years before body mass caught up.

Body size is one of the most important determinants of the biology of every organism on the planet

Manuel Will

̽��ֱ�� of Cambridge

Femoral head bones of different hominin species. From top to bottom: Australopithecus afarensis (4-3 million years; ~40 kg, 130 cm); Homo ergaster (1.9-1.4 million years; 55-60 kg; ~165 cm); Neanderthal (200.000-30.000 years; ~70 kg; ~163 cm).

̽��ֱ��text in this work is licensed under a Creative Commons Attribution 4.0 International License. For image use please see separate credits above.

Yes

One step for early hominins: Study reveals why our ancestors switched to bipedal power

bjb42 — Tue, 20 Mar 2012 00:01:55 +0000

A study published in the journal Current Biology this week (Tuesday, 20 March), investigated the behaviour of modern-day chimpanzees as they competed for food resources, in an effort to understand why our “hominin”, or “human-like” ancestors became bipedal.

Its findings suggest that chimpanzees switch to moving on two limbs instead of four in situations where they need to monopolise a resource, usually because it may not occur in plentiful supply in their habitat, making it hard for them to predict when they will see it again. Standing on two legs allows them to carry much more in one go because it frees up their hands.

̽��ֱ��joint ̽��ֱ�� of Cambridge and Kyoto ̽��ֱ�� team of biological anthropologists, led by PhD student Susana Carvalho and Professor Tetsuro Matsuzawa, conclude that our earliest hominin ancestors may have lived in shifting environmental conditions in which certain resources were not always easy to come by. Over time, intense bursts of bipedal activity may have led to anatomical changes that in turn became the subject of natural selection where competition for food or other resources was strong.

Lack of evidence in the fossil record means that researchers remain divided over when these ancestors became bipedal. It is widely believed that they did so because of climatic changes, which reduced forested areas and forced them to move longer distances across open terrain more often.

̽��ֱ��new research digs deeper, however, by attempting to explain what particular pressures within that context forced those hominins to modify their posture and resort to moving on their legs.

̽��ֱ��team theorised that the reason for this change may have something to do with the need to transport resources with maximum efficiency. Because bipedal movement is sometimes observed in modern great apes, they decided to monitor the behaviour of chimpanzees and, if possible, determine when and why they resorted to moving on two legs.

Two surveys were carried out. ̽��ֱ��first was in Kyoto ̽��ֱ��’s “outdoor laboratory” of a natural clearing in Bossou Forest, Guinea. Here, the researchers allowed the chimpanzees access to different combinations of two different types of nut – the oil palm nut, which is naturally widely available, and the coula nut, which is not, so the latter is an “unpredictable” resource.

Their behaviour was monitored in three different situations: (a) when only oil palm nuts were available, (b) when a small number of coula nuts was available, and (c) when coula nuts were the majority available resource.

When the rare coula nuts were available only in small numbers, the chimpanzees transported far more in one go. Similarly, when coula nuts were the majority resource, the chimpanzees ignored the oil palm nuts altogether. Clearly, the chimpanzees regarded the coula nuts as a more highly-prized resource and competed for them more intensely.

In such high-competition settings, the frequency of cases in which the chimpanzees started moving on two legs increased by a factor of four. Not only was it obvious that bipedal movement allowed them to carry more of this precious resource, but also that they were actively trying to move as much as they could in one go by using everything available – even their mouths.

̽��ֱ��second survey was a 14-month study of Bossou chimpanzees crop-raiding, a situation in which they have to compete for rare and unpredictable resources. Here, 35% of their activity involved some sort of bipedal movement, and once again, this behaviour appeared to be linked to a clear attempt to carry as much as possible in one go.

̽��ֱ��study concludes that unpredictable resources, like the coula nut in the field survey, are seen by chimpanzees as more valuable. When these resources are scarce and access to them is on a “first-come, first-served” basis, they are more prone to switch to bipedal movement, because it allows them to carry more of the resource at once.

For our early ancestors, unpredictable access to vital resources may have been a frequent occurrence because of climatic shifts and rapid environmental change. Those who resorted to bipedal movement may have had an advantage, and gradually, anatomical change may have taken place as they used this strategy again and again. Once that happened, ability to move more easily on two legs may have become a selection pressure, so that over many generations, it became the norm.

̽��ֱ��full report, Chimpanzee carrying behaviour and the origins of human bipedality, is available in the March 20 issue of Current Biology: https://www.cell.com/current-biology/

Our earliest ancestors may have started walking on two limbs instead of four in a bid to monopolise resources and to carry as much food as possible in one go, researchers have found.

Bipedality as the key human adaptation may be an evolutionary product of this strategy persisting over time. Ultimately, it set our ancestors on a separate evolutionary path.

William McGrew.

A chimpanzee moving bipedally during the study.

This work is licensed under a Creative Commons Licence. If you use this content on your site please link back to this page.

Yes