Publications by authors named "Andrew Du"

18 Publications

  • Page 1 of 1

Design and Fabrication of Glucose Biosensors Based on Immobilization of Glucose Oxidase on Titanium Oxide Nanotube Arrays.

J Nanosci Nanotechnol 2021 Sep;21(9):4605-4614

Science, Technology, Engineering and Mathematics (STEM-UniSA), University of South Australia, Adelaide, SA 5095, Australia.

An electrochemical biosensor for the detection of glucose is realized by immobilizing glucose oxidase (GOx) enzyme onto titanium dioxide nanotube arrays by a coupling encapsulation process. We present details of a robust fabrication technique that results in a durable and reproducible sensor characteristics. The TiO₂ nanotube arrays are grown directly on a titanium substrate by a potentiostatic anodization process in a water and ethylene-glycol mixture solution, which contains ammonium fluoride. An electropolymerization process was also performed to enhance interfacial adhesion between GOx and TiO₂ nanotubes. Detection of glucose concentrations was achieved with a linear response in the range of 0.01 to 0.2 mM. Investigation of enhanced sensitivity by increasing the count, the length, and the cross-section of the nanotubes was also carried out. Surface morphologies of Ti substrate were examined by scanning electron microscopy to optimize the anodization process and thus the TiO₂/Ti nanotube dimensions. We utilized a time-based amperometric response for the quantitative determination of hydrogen peroxide concentration through electro-reduction reaction with a bare TiO₂/Ti nanotube-array electrodes, thus providing a reference for the determination of glucose levels with a GOx-coated TiO₂/Ti nanotube array electrodes. Detection levels down to 5.2 M were recorded.
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http://dx.doi.org/10.1166/jnn.2021.19324DOI Listing
September 2021

Investigating Biotic Interactions in Deep Time.

Trends Ecol Evol 2021 01 13;36(1):61-75. Epub 2020 Oct 13.

School of Biological Sciences, University of Nebraska-Lincoln, Lincoln, NE, USA.

Recent renewed interest in using fossil data to understand how biotic interactions have shaped the evolution of life is challenging the widely held assumption that long-term climate changes are the primary drivers of biodiversity change. New approaches go beyond traditional richness and co-occurrence studies to explicitly model biotic interactions using data on fossil and modern biodiversity. Important developments in three primary areas of research include analysis of (i) macroevolutionary rates, (ii) the impacts of and recovery from extinction events, and (iii) how humans (Homo sapiens) affected interactions among non-human species. We present multiple lines of evidence for an important and measurable role of biotic interactions in shaping the evolution of communities and lineages on long timescales.
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http://dx.doi.org/10.1016/j.tree.2020.09.001DOI Listing
January 2021

Reply to Weihmann: Fifty gazelles do not equal an elephant, and other ecological misunderstandings.

Proc Natl Acad Sci U S A 2020 02 4;117(7):3370-3371. Epub 2020 Feb 4.

Department of Anthropology and Geography, Colorado State University, Fort Collins, CO 80523.

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http://dx.doi.org/10.1073/pnas.1920565117DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7035609PMC
February 2020

Statistical estimates of hominin origination and extinction dates: A case study examining the Australopithecus anamensis-afarensis lineage.

J Hum Evol 2020 01 20;138:102688. Epub 2019 Nov 20.

Department of Organismal Biology and Anatomy, The University of Chicago, Chicago, IL 60637, USA.

Reliable estimates of when hominin taxa originated and went extinct are central to addressing many paleoanthropological questions, including those relating to macroevolutionary patterns. The timing of hominin temporal ranges can be used to test chronological predictions generated from phylogenetic hypotheses. For example, hypotheses of phyletic ancestor-descendant relationships, based on morphological data, predict no temporal range overlap between the two taxa. However, a fossil taxon's observed temporal range is almost certainly underestimated due to the incompleteness of both the fossil record itself and its sampling, and this decreases the likelihood of observing temporal overlap. Here, we focus on a well-known and widely accepted early hominin lineage, Australopithecus anamensis-afarensis, and place 95% confidence intervals (CIs) on its origination and extinction dates. We do so to assess whether its temporal range is consistent with it being a phyletic descendant of Ardipithecus ramidus and/or a direct ancestor to the earliest claimed representative of Homo (i.e., Ledi-Geraru). We find that the last appearance of Ar. ramidus falls within the origination CI of Au. anamensis-afarensis, whereas the claimed first appearance of Homo postdates the extinction CI. These results are consistent with Homo evolving from Au. anamensis-afarensis, but temporal overlap between Ar. ramidus and Au. anamensis-afarensis cannot be rejected at this time. Though additional samples are needed, future research should extend our initial analyses to incorporate the uncertainties surrounding the range endpoints of Ar. ramidus and earliest Homo. Overall, our findings demonstrate the need for quantifying the uncertainty surrounding the appearances and disappearances of hominin taxa in order to better understand the timing of evolutionary events in our clade's history.
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http://dx.doi.org/10.1016/j.jhevol.2019.102688DOI Listing
January 2020

Evolution of the modern human brain.

Prog Brain Res 2019 5;250:219-250. Epub 2019 Mar 5.

Center for the Advanced Study of Human Paleobiology, Department of Anthropology, The George Washington University, Washington, DC, United States. Electronic address:

When compared to the brains of our closest living relatives, chimpanzees and bonobos, the brains of modern humans are larger and differently shaped. This chapter reviews what we know about the evolutionary history of these differences. We can make an educated guess about the size and shape of the brains of the hypothetical common ancestor of modern humans and chimpanzees/bonobos, but between ca. 8 million years ago and the present day evidence about the size and shape of the brain comes from either natural endocasts, which are literally brain-shaped rocks, or from individuals for which enough of the brain case is preserved to provide estimates of endocranial volume and/or the relative proportions of the different regions of the cerebral hemispheres and the cerebellum. The tempo and mode of brain size increase in the hominin clade has been the subject of spirited debate, but we suggest that some of this controversy is the combination of an overreliance on frequentist statistical tests and researchers addressing these issues at different taxonomic scales. The existence and significance of shape changes are also controversial topics, made more so by the dearth of reliable evidence.
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http://dx.doi.org/10.1016/bs.pbr.2019.01.004DOI Listing
June 2020

Reorganization of surviving mammal communities after the end-Pleistocene megafaunal extinction.

Science 2019 09;365(6459):1305-1308

Department of Biological Sciences, Macquarie University, New South Wales 2109, Australia.

Large mammals are at high risk of extinction globally. To understand the consequences of their demise for community assembly, we tracked community structure through the end-Pleistocene megafaunal extinction in North America. We decomposed the effects of biotic and abiotic factors by analyzing co-occurrence within the mutual ranges of species pairs. Although shifting climate drove an increase in niche overlap, co-occurrence decreased, signaling shifts in biotic interactions. Furthermore, the effect of abiotic factors on co-occurrence remained constant over time while the effect of biotic factors decreased. Biotic factors apparently played a key role in continental-scale community assembly before the extinctions. Specifically, large mammals likely promoted co-occurrence in the Pleistocene, and their loss contributed to the modern assembly pattern in which co-occurrence frequently falls below random expectations.
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http://dx.doi.org/10.1126/science.aaw1605DOI Listing
September 2019

Early hominins evolved within non-analog ecosystems.

Proc Natl Acad Sci U S A 2019 10 7;116(43):21478-21483. Epub 2019 Oct 7.

Department of Anthropology and Geography, Colorado State University, Fort Collins, CO 80523.

Present-day African ecosystems serve as referential models for conceptualizing the environmental context of early hominin evolution, but the degree to which modern ecosystems are representative of those in the past is unclear. A growing body of evidence from eastern Africa's rich and well-dated late Cenozoic fossil record documents communities of large-bodied mammalian herbivores with ecological structures differing dramatically from those of the present day, implying that modern communities may not be suitable analogs for the ancient ecosystems of hominin evolution. To determine when and why the ecological structure of eastern Africa's herbivore faunas came to resemble those of the present, here we analyze functional trait changes in a comprehensive dataset of 305 modern and fossil herbivore communities spanning the last ∼7 Myr. We show that nearly all communities prior to ∼700 ka were functionally non-analog, largely due to a greater richness of non-ruminants and megaherbivores (species >1,000 kg). The emergence of functionally modern communities precedes that of taxonomically modern communities by 100,000s of years, and can be attributed to the combined influence of Plio-Pleistocene C grassland expansion and pulses of aridity after ∼1 Ma. Given the disproportionate ecological impacts of large-bodied herbivores on factors such as vegetation structure, hydrology, and fire regimes, it follows that the vast majority of early hominin evolution transpired in the context of ecosystems that functioned unlike any today. Identifying how past ecosystems differed compositionally and functionally from those today is key to conceptualizing ancient African environments and testing ecological hypotheses of hominin evolution.
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http://dx.doi.org/10.1073/pnas.1909284116DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6815188PMC
October 2019

Temporal evidence shows is unlikely to be the ancestor of .

Sci Adv 2019 05 8;5(5):eaav9038. Epub 2019 May 8.

Department of Organismal Biology and Anatomy, The University of Chicago, Chicago, IL 60637, USA.

Understanding the emergence of the genus is a pressing problem in the study of human origins. has recently been proposed as the ancestral species of , although it postdates earliest by 800,000 years. Here, we use probability models to demonstrate that observing an ancestor's fossil horizon that is at least 800,000 years younger than the descendant's fossil horizon is unlikely (about 0.09% on average). We corroborate these results by searching the literature and finding that within pairs of purported hominin ancestor-descendant species, in only one case did the first-discovered fossil in the ancestor postdate that from the descendant, and the age difference between these fossils was much less than the difference observed between and earliest . Together, these results suggest it is highly unlikely that is ancestral to , and the most viable candidate ancestral species remains .
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http://dx.doi.org/10.1126/sciadv.aav9038DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6506247PMC
May 2019

Plio-Pleistocene decline of African megaherbivores: No evidence for ancient hominin impacts.

Science 2018 11;362(6417):938-941

Department of Earth and Planetary Sciences, University of California, Santa Cruz, CA 95064, USA.

It has long been proposed that pre-modern hominin impacts drove extinctions and shaped the evolutionary history of Africa's exceptionally diverse large mammal communities, but this hypothesis has yet to be rigorously tested. We analyzed eastern African herbivore communities spanning the past 7 million years-encompassing the entirety of hominin evolutionary history-to test the hypothesis that top-down impacts of tool-bearing, meat-eating hominins contributed to the demise of megaherbivores prior to the emergence of We document a steady, long-term decline of megaherbivores beginning ~4.6 million years ago, long before the appearance of hominin species capable of exerting top-down control of large mammal communities and predating evidence for hominin interactions with megaherbivore prey. Expansion of C grasslands can account for the loss of megaherbivore diversity.
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http://dx.doi.org/10.1126/science.aau2728DOI Listing
November 2018

Diversity analysis of Plio-Pleistocene large mammal communities in the Omo-Turkana Basin, eastern Africa.

J Hum Evol 2018 11 25;124:25-39. Epub 2018 Aug 25.

Department of Organismal Biology and Anatomy, The University of Chicago, 1027 E 57th St, Chicago, IL 60637, USA.

Knowing how the diversity of large mammal communities changes across space and time provides an important ecological framework for studying hominin evolution. However, diversity studies that apply methods currently used by neoecologists are rare in paleoanthropology and are also challenging due to diversity's unusual statistical properties. Here, we apply up-to-date analytical methods for understanding how species- and genus-level large mammalian diversity in the Omo-Turkana Basin changed through time and across space at multiple spatiotemporal scales (within each formation:10 km and 10 years; and within the basin as a whole: 10 km and 10 years). We found that, on average, Koobi Fora's large mammal community was more diverse than Nachukui's, which in turn was more diverse than Shungura's. Diversity was stable through time within each of these formations (alpha diversity), as was diversity in the basin as a whole (gamma diversity). Compositional dissimilarity between these three formations (beta diversity) was relatively low through time, with a 0.6 average proportion of shared species, suggesting dispersal acted to homogenize the region. Though alpha and gamma diversity were fairly stable through time, we do observe several notable peaks: during the KBS Member in Koobi Fora (30% increase), the Lokalalei Member in Nachukui (120% increase), and at 1.7 Ma in the entire basin (100% increase). We conclude by (1) demonstrating that habitat heterogeneity was an important factor influencing alpha diversity within each of the three formations, and (2) hypothesizing that diversity stability may have been driven by equilibrial dynamics in which overall diversity was constrained by resource availability, implying biotic interactions were an important factor in structuring the communities that included hominins as members. Our findings demonstrate the need to quantify how large mammal diversity changes across time and space in order to further our understanding of hominin ecology and evolution.
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http://dx.doi.org/10.1016/j.jhevol.2018.07.004DOI Listing
November 2018

Pleistocene animal communities of a 1.5 million-year-old lake margin grassland and their relationship to Homo erectus paleoecology.

J Hum Evol 2018 09 30;122:70-83. Epub 2018 Jun 30.

Division of Anthropology, American Museum of Natural History, Central Park West at 79th Street, New York, NY 10024, USA; Department of Human Evolution, Max Planck Institute for Evolutionary Anthropology, Deutscher Platz 6, D-04103 Leipzig, Germany.

The ecological and selective forces that sparked the emergence of Homo's adaptive strategy remain poorly understood. New fossil and archaeological finds call into question previous interpretations of the grade shift that drove our ancestors' evolutionary split from the australopiths. Furthermore, issues of taphonomy and scale have limited reconstructions of the hominin habitats and faunal communities that define the environmental context of these behavioral changes. The multiple ∼1.5 Ma track surfaces from the Okote Member of the Koobi Fora Formation at East Turkana provide unique windows for examining hominin interactions with the paleoenvironment and associated faunas at high spatiotemporal resolution. These surfaces preserve the tracks of many animals, including cf. Homo erectus. Here, we examine the structure of the animal community that inhabited this landscape, considering effects of preservation bias by comparing the composition of the track assemblage to a skeletal assemblage from the same time and place. We find that the track and skeletal assemblages are similar in their representation of the vertebrate paleocommunity, with comparable levels of taxonomic richness and diversity. Evenness (equitability of the number of individuals per taxon) differs between the two assemblages due to the very different circumstances of body fossil versus track preservation. Both samples represent diverse groups of taxa including numerous water-dependent species, consistent with geological interpretations of the track site environments. Comparisons of these assemblages also show a pattern of non-random hominin association with a marginal lacustrine habitat relative to other vertebrates in the track assemblage. This evidence is consistent with behavior that included access to aquatic foods and possibly hunting by H. erectus in lake margins/edaphic grasslands. Such behaviors may signal the emergence of the adaptative strategies that define our genus.
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http://dx.doi.org/10.1016/j.jhevol.2018.04.014DOI Listing
September 2018

Pattern and process in hominin brain size evolution are scale-dependent.

Proc Biol Sci 2018 02;285(1873)

Center for the Advanced Study of Human Paleobiology, Department of Anthropology, The George Washington University, 800 22nd Street, NW, Washington, DC 20052, USA.

A large brain is a defining feature of modern humans, yet there is no consensus regarding the patterns, rates and processes involved in hominin brain size evolution. We use a reliable proxy for brain size in fossils, endocranial volume (ECV), to better understand how brain size evolved at both clade- and lineage-level scales. For the hominin clade overall, the dominant signal is consistent with a gradual increase in brain size. This gradual trend appears to have been generated primarily by processes operating within hypothesized lineages-64% or 88% depending on whether one uses a more or less speciose taxonomy, respectively. These processes were supplemented by the appearance in the fossil record of larger-brained species and the subsequent disappearance of smaller-brained and taxa. When the estimated rate of within-lineage ECV increase is compared to an exponential model that operationalizes generation-scale evolutionary processes, it suggests that the observed data were the result of episodes of directional selection interspersed with periods of stasis and/or drift; all of this occurs on too fine a timescale to be resolved by the current human fossil record, thus producing apparent gradual trends within lineages. Our findings provide a quantitative basis for developing and testing scale-explicit hypotheses about the factors that led brain size to increase during hominin evolution.
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http://dx.doi.org/10.1098/rspb.2017.2738DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5832710PMC
February 2018

Pleistocene footprints show intensive use of lake margin habitats by Homo erectus groups.

Sci Rep 2016 05 20;6:26374. Epub 2016 May 20.

Division of Anthropology, American Museum of Natural History, New York, New York 10024, USA.

Reconstructing hominin paleoecology is critical for understanding our ancestors' diets, social organizations and interactions with other animals. Most paleoecological models lack fine-scale resolution due to fossil hominin scarcity and the time-averaged accumulation of faunal assemblages. Here we present data from 481 fossil tracks from northwestern Kenya, including 97 hominin footprints attributed to Homo erectus. These tracks are found in multiple sedimentary layers spanning approximately 20 thousand years. Taphonomic experiments show that each of these trackways represents minutes to no more than a few days in the lives of the individuals moving across these paleolandscapes. The geology and associated vertebrate fauna place these tracks in a deltaic setting, near a lakeshore bordered by open grasslands. Hominin footprints are disproportionately abundant in this lake margin environment, relative to hominin skeletal fossil frequency in the same deposits. Accounting for preservation bias, this abundance of hominin footprints indicates repeated use of lakeshore habitats by Homo erectus. Clusters of very large prints moving in the same direction further suggest these hominins traversed this lakeshore in multi-male groups. Such reliance on near water environments, and possibly aquatic-linked foods, may have influenced hominin foraging behavior and migratory routes across and out of Africa.
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http://dx.doi.org/10.1038/srep26374DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4873780PMC
May 2016

Holocene shifts in the assembly of plant and animal communities implicate human impacts.

Nature 2016 Jan 16;529(7584):80-3. Epub 2015 Dec 16.

Department of Biology, University of Vermont, Burlington, Vermont 05405, USA.

Understanding how ecological communities are organized and how they change through time is critical to predicting the effects of climate change. Recent work documenting the co-occurrence structure of modern communities found that most significant species pairs co-occur less frequently than would be expected by chance. However, little is known about how co-occurrence structure changes through time. Here we evaluate changes in plant and animal community organization over geological time by quantifying the co-occurrence structure of 359,896 unique taxon pairs in 80 assemblages spanning the past 300 million years. Co-occurrences of most taxon pairs were statistically random, but a significant fraction were spatially aggregated or segregated. Aggregated pairs dominated from the Carboniferous period (307 million years ago) to the early Holocene epoch (11,700 years before present), when there was a pronounced shift to more segregated pairs, a trend that continues in modern assemblages. The shift began during the Holocene and coincided with increasing human population size and the spread of agriculture in North America. Before the shift, an average of 64% of significant pairs were aggregated; after the shift, the average dropped to 37%. The organization of modern and late Holocene plant and animal assemblages differs fundamentally from that of assemblages over the past 300 million years that predate the large-scale impacts of humans. Our results suggest that the rules governing the assembly of communities have recently been changed by human activity.
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http://dx.doi.org/10.1038/nature16447DOI Listing
January 2016

Primate archaeology.

Nature 2009 Jul;460(7253):339-44

Leverhulme Centre for Human Evolutionary Studies, University of Cambridge, Cambridge CB2 1QH, UK.

All modern humans use tools to overcome limitations of our anatomy and to make difficult tasks easier. However, if tool use is such an advantage, we may ask why it is not evolved to the same degree in other species. To answer this question, we need to bring a long-term perspective to the material record of other members of our own order, the Primates.
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http://dx.doi.org/10.1038/nature08188DOI Listing
July 2009