Homo Paedens? Did Kids Invent the Human Species?

The evolution of development (“evo-devo”) has become a central concern in both evolu­tionary and developmental research, and human immaturity is no less a proper focus for evolutionary analysis than that of other species-if anything, it is more so. Two new books by David F. Bjorklund, a founder of evolutionary developmental psychology, summarize what we know now and propose that children invented our species. Due to the new phe­nomenon of partly heritable epigenetic modification of genes and the old one of the Bald­win Effect (by which plasticity leads to new selective forces on genes), this claim must be at least partly true. The inherent plasticity of children’s behavior, including play, accelerat­ed the evolution of humanity as instantiated in the human brain. Evolution cannot be understood without extensive reference to development, and nothing in childhood makes sense except in the light of evolution.

Genomic approaches to trace the history of human brain evolution with an emerging opportunity for transposon profiling of ancient humans

Transposable elements (TEs) significantly contribute to shaping the diversity of the human genome, and lines of evidence suggest TEs as one of driving forces of human brain evolution. Existing computational approaches, including cross-species comparative genomics and population genetic modeling, can be adapted for the study of the role of TEs in evolution. In particular, diverse ancient and archaic human genome sequences are increasingly available, allowing reconstruction of past human migration events and holding the promise of identifying and tracking TEs among other evolutionarily important genetic variants at an unprecedented spatiotemporal resolution. However, highly degraded short DNA templates and other unique challenges presented by ancient human DNA call for major changes in current experimental and computational procedures to enable the identification of evolutionarily important TEs. Ancient human genomes are valuable resources for investigating TEs in the evolutionary context, and efforts to explore ancient human genomes will potentially provide a novel perspective on the genetic mechanism of human brain evolution and inspire a variety of technological and methodological advances. In this review, we summarize computational and experimental approaches that can be adapted to identify and validate evolutionarily important TEs, especially for human brain evolution. We also highlight strategies that leverage ancient genomic data and discuss unique challenges in ancient transposon genomics.

The Significance of Chimpanzee Occipital Asymmetry to Hominin Evolution

Little is known about how occipital lobe asymmetry, width, and height interact to contribute to the operculation of the posterior parietal lobe, despite the utility of knowing this for understanding the relative reduction in the size of the occipital lobe and the increase in the size of the posterior parietal lobe during human brain evolution. Here, we use linear measurements taken on 3D virtual brain surfaces obtained from 83 chimpanzees to study these traits as they apply to operculation of the posterior occipital parietal arcus or bridging gyrus. Asymmetry in this bridging gyrus visibility provides a unique opportunity to study both the human ancestral and human equivalently normal condition in the same individual. Our results show that all three traits (occipital lobe asymmetry, width, and height) are related to this operculation and bridging gyrus visibility but width and not height is the best predictor, against expectations, suggesting that relative reduction of the occipital lobe and exposure of the posterior parietal is a complex phenomenon.

Five Breakthroughs: A First Approximation of Brain Evolution From Early Bilaterians to Humans

Retracing the evolutionary steps by which human brains evolved can offer insights into the underlying mechanisms of human brain function as well as the phylogenetic origin of various features of human behavior. To this end, this article presents a model for interpreting the physical and behavioral modifications throughout major milestones in human brain evolution. This model introduces the concept of a “breakthrough” as a useful tool for interpreting suites of brain modifications and the various adaptive behaviors these modifications enabled. This offers a unique view into the ordered steps by which human brains evolved and suggests several unique hypotheses on the mechanisms of human brain function.

What Behavioral Abilities Emerged at Key Milestones in Human Brain Evolution? 13 Hypotheses on the 600-Million-Year Phylogenetic History of Human Intelligence

This paper presents 13 hypotheses regarding the specific behavioral abilities that emerged at key milestones during the 600-million-year phylogenetic history from early bilaterians to extant humans. The behavioral, intellectual, and cognitive faculties of humans are complex and varied: we have abilities as diverse as map-based navigation, theory of mind, counterfactual learning, episodic memory, and language. But these faculties, which emerge from the complex human brain, are likely to have evolved from simpler prototypes in the simpler brains of our ancestors. Understanding the order in which behavioral abilities evolved can shed light on how and why our brains evolved. To propose these hypotheses, I review the available data from comparative psychology and evolutionary neuroscience.

Tool and Symbol

This chapter examines the emergence of tool use and human language in human brain evolution. Increasing use and design of tools made possible by the bipedalism of our proto-human ancestors was a key step in the development of language. Indeed, communal tool use ‘helped to bring the members of society together by increasing the cases of mutual support and joint activity’. During this process, ‘the reaction of labour and speech on the development of the brain and its attendant senses, of the increasing clarity of consciousness, power of abstraction and of conclusion, gave both labour and speech an ever renewed impulse to further development’. The chapter then considers the studies which assess the fundamental differences in terms of language capacity between humans and apes. While the behaviourist view that human language acquisition is simply an accumulation of conditioned reflexes now looks incorrect, recent studies have also challenged the view of a biological basis for a ‘universal grammar’ shared by all humans. Instead, increasing evidence points to both human biology and the process of growing up in a specific human society as being factors of equal importance in the formation of language.

Evolution of DNA methylation in the human brain

DNA methylation is a critical regulatory mechanism implicated in development, learning, memory, and disease in the human brain. Here we have elucidated DNA methylation changes during recent human brain evolution. We demonstrate dynamic evolutionary trajectories of DNA methylation in cell-type and cytosine-context specific manner. Specifically, DNA methylation in non-CG context, namely CH methylation, has increased (hypermethylation) in neuronal gene bodies during human brain evolution, contributing to human-specific down-regulation of genes and co-expression modules. The effects of CH hypermethylation is particularly pronounced in early development and neuronal subtypes. In contrast, DNA methylation in CG context shows pronounced reduction (hypomethylation) in human brains, notably in cis-regulatory regions, leading to upregulation of downstream genes. We show that the majority of differential CG methylation between neurons and oligodendrocytes originated before the divergence of hominoids and catarrhine monkeys, and harbors strong signal for genetic risk for schizophrenia. Remarkably, a substantial portion of differential CG methylation between neurons and oligodendrocytes emerged in the human lineage since the divergence from the chimpanzee lineage and carries significant genetic risk for schizophrenia. Therefore, recent epigenetic evolution of human cortex has shaped the cellular regulatory landscape and contributed to the increased vulnerability to neuropsychiatric diseases.