Friday, 7 May 2021

Evolution News - Putting the Pieces of The Puzzle Together

Extant and fossil ape distribution.


Extant apes live in (or nearby) densely forested areas around the equator in Africa and Southeast Asia. Except for the recently recognized tapanuli orangutan (which may represent a subspecies of the Sumatran orangutan), each of the three extant great ape genera presently has two geographically separated species. The Congo River (highlighted in dark blue) acts as the current barrier between common chimpanzees (Pan troglodytes) and bonobos (Pan paniscus). Red stars indicate regions with Miocene sediments (spanning ~23 to 5.3 Ma) where fossil apes have been uncovered. (Some regions may contain more than one site; contiguous regions are indicated with different stars if they extend over more than one political zone.) It is possible that modern great ape habitats do not represent the ancestral environments where the great ape and human clade evolved. Paleontologically, the vast majority of Africa, west of the Rift Valley, remains highly unexplored. Extant ape ranges were taken from the International Union for Conservation of Nature (IUCN Red List).

Background image sources: Esri, DigitalGlobe, GeoEye, i-cubed, USDA FSA, USGS, AEX, Getmapping, Aerogrid, IGN, IGP, swisstopo, and the GIS user community.
Review: Human Origins Stories Incompatible with Known Fossils | AMNH

Reconstructing the evolutionary history of a species often resembles creating the picture in a jigsaw puzzle from only a few pieces. The many gaps will be inevitable and there is no real certainty about the resulting picture.

This is especially true of the evolutionary history of the hominins, for example. But one thing is certain: none of it makes any sense other than as the picture of an evolutionary process, as this review of the known evidence by researchers from the American Museum of Natural History show in their paper published in Science today shows.

Although the evidence is far from complete, nowhere is there evidence of that forlorn Creationist lie that the TOE is a theory in crisis, about to be replaced by magic creationism, as the first ever scientific theory to be replaced by evidence-free supernaturalism with a god and god-magic inserted in every conceivable gap.

Paradoxically, the picture is often made more complicated and uncertain, not less, with the discovery of more fossils of 'transitional' species, because it is often not obvious just how this or that latest find fits in with the overall picture (we do not have a picture on the lid to follow). Despite the false claims of Creationist frauds that science doesn't have any 'transitional' species (is it only human evolution that worries them?) science actually has so many it's difficult to know what to do with them all, so far as fitting them into a coherent, evidence-based narrative goes.

This is made clear in the opening paragraph of the press release from AMNH:
In the 150 years since Charles Darwin speculated that humans originated in Africa, the number of species in the human family tree has exploded, but so has the level of dispute concerning early human evolution. Fossil apes are often at the center of the debate, with some scientists dismissing their importance to the origins of the human lineage (the “hominins”), and others conferring them starring evolutionary roles. A new review out on May 7 in the journal Science looks at the major discoveries in hominin origins since Darwin’s works and argues that fossil apes can inform us about essential aspects of ape and human evolution, including the nature of our last common ancestor.

When you look at the narrative for hominin origins, it’s just a big mess—there’s no consensus whatsoever. People are working under completely different paradigms, and that’s something that I don’t see happening in other fields of science.

Sergio Almécija, Lead author
Senior research scientist
Division of Anthropology
American Museum of Natural History.
Humans diverged from apes—specifically, the chimpanzee lineage—at some point between about 9.3 million and 6.5 million years ago, towards the end of the Miocene epoch. To understand hominin origins, paleoanthropologists aim to reconstruct the physical characteristics, behavior, and environment of the last common ancestor of humans and chimps.

[...]

There are two major approaches to resolving the human origins problem: “Top-down,” which relies on analysis of living apes, especially chimpanzees; and “bottom-up,” which puts importance on the larger tree of mostly extinct apes. For example, some scientists assume that hominins originated from a chimp-like knuckle-walking ancestor. Others argue that the human lineage originated from an ancestor more closely resembling, in some features, some of the strange Miocene apes.
In The Descent of Man in 1871, Darwin speculated that humans originated in Africa from an ancestor different from any living species. However, he remained cautious given the scarcity of fossils at the time. One hundred fifty years later, possible hominins—approaching the time of the human-chimpanzee divergence—have been found in eastern and central Africa, and some claim even in Europe. In addition, more than 50 fossil ape genera are now documented across Africa and Eurasia. However, many of these fossils show mosaic combinations of features that do not match expectations for ancient representatives of the modern ape and human lineages. As a consequence, there is no scientific consensus on the evolutionary role played by these fossil apes.

Current disparate theories regarding ape and human evolution would be much more informed if, together with early hominins and living apes, Miocene apes were also included in the equation. In other words, fossil apes are essential to reconstruct the ‘starting point’ from which humans and chimpanzees evolved.

Sergio Almécija
But there is no problem per se with having two major approaches as both are capable of producing results and neither approach produces a complete answer, as the rest of the press release explains:
In reviewing the studies surrounding these diverging approaches, Almécija and colleagues with expertise ranging from paleontology to functional morphology and phylogenetics discuss the limitations of relying exclusively on one of these opposing approaches to the hominin origins problem. “Top-down” studies sometimes ignore the reality that living apes (humans, chimpanzees, gorillas, orangutans, and hylobatids) are just the survivors of a much larger, and now mostly extinct, group. On the other hand, studies based on the “bottom-up” approach are prone to giving individual fossil apes an important evolutionary role that fits a preexisting narrative.

“In The Descent of Man in 1871, Darwin speculated that humans originated in Africa from an ancestor different from any living species. However, he remained cautious given the scarcity of fossils at the time,” Almécija said. “One hundred fifty years later, possible hominins—approaching the time of the human-chimpanzee divergence—have been found in eastern and central Africa, and some claim even in Europe. In addition, more than 50 fossil ape genera are now documented across Africa and Eurasia. However, many of these fossils show mosaic combinations of features that do not match expectations for ancient representatives of the modern ape and human lineages. As a consequence, there is no scientific consensus on the evolutionary role played by these fossil apes.”

Living ape species are specialized species, relicts of a much larger group of now extinct apes. When we consider all evidence—that is, both living and fossil apes and hominins—it is clear that a human evolutionary story based on the few ape species currently alive is missing much of the bigger picture.

Ashley Hammond, Co-author
Assistant curator
Division of Anthropology
American Museum of Natural History.
Overall, the researchers found that most stories of human origins are not compatible with the fossils that we have today.

“Living ape species are specialized species, relicts of a much larger group of now extinct apes. When we consider all evidence—that is, both living and fossil apes and hominins—it is clear that a human evolutionary story based on the few ape species currently alive is missing much of the bigger picture.

Kelsey Pugh, a Museum postdoctoral fellow and study co-author adds, “The unique and sometimes unexpected features and combinations of features observed among fossil apes, which often differ from those of living apes, are
The unique and sometimes unexpected features and combinations of features observed among fossil apes, which often differ from those of living apes, are necessary to untangle which features hominins inherited from our ape ancestors and which are unique to our lineage.

Kelsey Pugh, Co-author
Postdoctoral fellow
American Museum of Natural History
necessary to untangle which features hominins inherited from our ape ancestors and which are unique to our lineage.”

Living apes alone, the authors conclude, offer insufficient evidence. “Current disparate theories regarding ape and human evolution would be much more informed if, together with early hominins and living apes, Miocene apes were also included in the equation,” says Almécija. “In other words, fossil apes are essential to reconstruct the ‘starting point’ from which humans and chimpanzees evolved.”
More detail is given in the structured abstract to their paper in Nature:
Structured Abstract

BACKGROUND

Ever since the writings of Darwin and Huxley, humans’ place in nature relative to apes (nonhuman hominoids) and the geographic origins of the human lineage (hominins) have been heavily debated. Humans diverged from apes [specifically, the chimpanzee lineage (Pan)] at some point between ~9.3 million and ~6.5 million years ago (Ma), and habitual bipedalism evolved early in hominins (accompanied by enhanced manipulation and, later on, cognition). To understand the selective pressures surrounding hominin origins, it is necessary to reconstruct the morphology, behavior, and environment of the Pan-Homo last common ancestor (LCA). “Top-down” approaches have relied on living apes (especially chimpanzees) to reconstruct hominin origins. However, “bottom-up” perspectives from the fossil record suggest that modern hominoids represent a decimated and biased sample of a larger ancient radiation and present alternative possibilities for the morphology and geography of the Pan-Homo LCA. Reconciling these two views remains at the core of the human origins problem.

ADVANCES

There is no consensus on the phylogenetic positions of the diverse and widely distributed Miocene apes. Besides their fragmentary record, disagreements are due to the complexity of interpreting fossil morphologies that present mosaics of primitive and derived features, likely because of parallel evolution (i.e., homoplasy). This has led some authors to exclude known Miocene apes from the modern hominoid radiation. However, most researchers identify some fossil apes as either stem or crown members of the hominid clade [i.e., preceding the divergence between orangutans (pongines) and African great apes and humans (hominines), or as a part of the modern great ape radiation]. European Miocene apes have prominently figured in discussions about the geographic origin of hominines. “Kenyapith” apes dispersed from Africa into Eurasia ~16 to 14 Ma, and some of them likely gave rise to the European “dryopith” apes and the Asian pongines before 12.5 Ma. Some authors interpret dryopiths as stem hominines and support their back-to-Africa dispersal in the latest Miocene, subsequently evolving into modern African apes and hominins. Others interpret dryopiths as broadly ancestral to hominids or an evolutionary dead end.

Increased habitat fragmentation during the late Miocene in Africa might explain the evolution of African ape knuckle walking and hominin bipedalism from an orthograde arboreal ancestor. Bipedalism might have allowed humans to escape the great ape “specialization trap“—an adaptive feedback loop between diet, specialized arboreal locomotion, cognition, and life history. However, understanding the different selection pressures that underlie knuckle walking and bipedalism is hindered by locomotor uncertainties about the Pan-Homo LCA and its Miocene forebears. In turn, the functional interpretation of Miocene ape mosaic morphologies is challenging because it depends on the relevance of primitive features. Furthermore, adaptive complexes can be co-opted to perform new functions during evolution. For instance, features that are functionally related to quadrupedalism or orthogrady can be misinterpreted as bipedal adaptations. Miocene apes show that the orthograde body plan, which predates below-branch suspension, is likely an adaptation for vertical climbing that was subsequently co-opted for other orthograde behaviors, including habitual bipedalism.

The evolutionary history of apes and humans is largely incomplete.


Whereas the phylogenetic relationships among living species can be retrieved using genetic data, the position of most extinct species remains contentious. Surprisingly, complete-enough fossils that can be attributed to the gorilla and chimpanzee lineages remain to be discovered. Assuming different positions of available fossil apes (or ignoring them owing to uncertainty) markedly affects reconstructions of key ancestral nodes, such as that of the chimpanzee-human LCA.

OUTLOOK

Future research efforts on hominin origins should focus on (i) fieldwork in unexplored areas where Miocene apes have yet to be found, (ii) methodological advances in morphology-based phylogenetics and paleoproteomics to retrieve molecular data beyond ancient DNA limits, and (iii) modeling driven by experimental data that integrates morphological and biomechanical information, to test locomotor inferences for extinct taxa. It is also imperative to stop assigning a starring role to each new fossil discovery to fit evolutionary scenarios that are not based on testable hypotheses.

Early hominins likely originated in Africa from a Miocene LCA that does not match any living ape (e.g., it might not have been adapted specifically for suspension or knuckle walking). Despite phylogenetic uncertainties, fossil apes remain essential to reconstruct the “starting point” from which humans and chimpanzees evolved.

Abstract

Humans diverged from apes (chimpanzees, specifically) toward the end of the Miocene ~9.3 million to 6.5 million years ago. Understanding the origins of the human lineage (hominins) requires reconstructing the morphology, behavior, and environment of the chimpanzee-human last common ancestor. Modern hominoids (that is, humans and apes) share multiple features (for example, an orthograde body plan facilitating upright positional behaviors). However, the fossil record indicates that living hominoids constitute narrow representatives of an ancient radiation of more widely distributed, diverse species, none of which exhibit the entire suite of locomotor adaptations present in the extant relatives. Hence, some modern ape similarities might have evolved in parallel in response to similar selection pressures. Current evidence suggests that hominins originated in Africa from Miocene ape ancestors unlike any living species.

So, given what these experts say about the fossil evidence for humun evolution from a common ancestor with the other African apes and how best to use it, would any creationist like to explain why this shows evidence for Creationism and a 'theory in crisis' as Creationist frauds like Ken Ham, Michael Behe, et al. continue to insist? If not, from where do these frauds get the evidence for their claims?

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