A recent study published within the Communications Biology Journal summarized the knowledge of brain anatomy from fossil records and brain evolution.
Study: From fossils to mind. Image Credit: 80’sChild/Shutterstock.com
Background
Since the brain doesn’t fossilize like bones and teeth, observing endocranium is the one approach to understand extinct species’ external brain anatomy.
The human brain may be best understood by comparing closely and distantly related species. Homo sapiens is a hominids (great apes) member, with bonobos and chimpanzees being the closest extant relatives.
Hominins include Homo sapiens and fossil species more closely related to humans than bonobos or chimpanzees. Several hominin species have evolved and develop into extinct prior to now six-seven million years.
In the current study, the authors reviewed brain anatomy from fossil records, focusing mainly on hominins, and discussed the knowledge gaps in brain evolution and the advances in the sphere.
Data from endocasts
Endocasts are man-made or natural internal casts of the endocranium, resembling brains, that provide data on just a few gross anatomical features. The study of the brain evolution of extinct species was possible because of endocast techniques. Fossil endocranial imprints can provide information on brain size, vasculature, and morphological features.
Studies of vascular imprints in fossil endocasts revealed specific patterns in early hominins. Vascular system reorganization in early hominins is interpreted as evidence for the looks of a thermoregulatory system to chill down the brain under hyperthermic conditions. The scale of arteries can provide details about blood flow and glucose utilization within the brain.
Various brain functions are lateralized in humans and other vertebrates. Behavioral lateralization in non-human primates and humans is said to hemispheric asymmetry within the anatomy of brain regions and morphology of the corpus callosum. Humans show more robust and consistent functional lateralization patterns.
A study measuring patterns and magnitude of asymmetry in endocranial shape reported that humans, orangutans, and gorillas have in regards to the same magnitude of asymmetry, however the endocasts of chimpanzees were less asymmetrical.
One other research team revealed that chimpanzees, orangutans, and gorillas exhibited asymmetry patterns typical of humans, difficult the notion that human asymmetry is exclusive.
Unresolved questions
The brain is probably the most energy-demanding tissues within the mammalian body. The adult human brain constitutes as much as 2% of the body mass but consumes 20% of the energy intake. Determining how human brains operate on different energy budgets than others requires more information on other species’ brain energetics.
It also stays unclear whether human brains are specialized for toolmaking and if their behavioral repertoires are related to brain organization, independent of size.
Answers to those would require knowledge of how brain structures relate to human behavior and other species. More evidence on cross-species brain development might help understand whether human brains are specialized for plasticity.
Emerging directions
Emerging directions for future research involve paleo-neurological collections incorporating neuroimaging, cellular and molecular biology, comparative phylogenetic techniques, paleo-anthropological discoveries, and sharing tools and data.
Latest avenues have emerged to look at hominin brain evolution by integrating endocast data with neuroimaging.
Although phylogenetic approaches are widely utilized in evolutionary biology, their use has been more limited regarding fossil hominins.
These approaches might help explore ancestral states in hominin brain evolution and discover differences in evolutionary rates for some hominin phylogenic branches. They will also be used to enhance brain structural predictions in extinct hominins.
Analyses of ancient DNA (aDNA) have revealed shared coding changes within the forkhead box protein P2 (FOXP2) gene linked to some types of brain plasticity in humans, Denisovans, and Neanderthals. Phylogenetic comparative methods might be leveraged to reconstruct fossil genomes from extant species’ genomes when aDNA is unavailable.
Organoids are instrumental in studies of extinct and extant species. The gene expression spatial patterns in brain organoids resemble the spatial layout of the brain, facilitating comparisons between species. Organoids adequately resemble nervous systems and may be used to know developmental differences across species.
Concluding remarks
Notwithstanding the similarities with other mammalian brains, the human brain stays an outlier in comparison with the brains of the closest relatives.
Newer biomedical, ecological, and geological science techniques may offer opportunities for archeologists and paleontologists, which could have broader applications.
The mix of approaches including, but not limited to, comparative phylogenetic methods, latest aDNA datasets, novel experimental strategies and advanced techniques to check the endocranium, archeological evidence, and sharing resources can offer latest possibilities to check fossil hominin brain evolution.