How did our distinctive brains evolve? What genetic changes, coupled with natural selection, gave us language? What allowed modern humans to form complex societies, pursue science, create art?
While we have some understanding of the genes that differentiate us from other primates, that knowledge cannot fully explain human brain evolution. But with a $10 million grant to some of Boston’s most highly evolved minds in genetics, genomics, neuroscience and human evolution, some answers may emerge in the coming years.
The Seattle-based Paul G. Allen Frontiers Group today announced the creation of an Allen Discovery Center for Human Brain Evolution at Boston Children’s Hospital and Harvard Medical School. It will be led by Christopher A. Walsh, MD, PhD, chief of the Division of Genetics and Genomics at Boston Children’s and a Howard Hughes Medical Institute investigator.
“To understand when and how our modern brains evolved, we need to take a multi-pronged approach that will reflect how evolution works in nature, and identifies how experience and environment affect the genes that gave rise to modern human behavior,” Walsh says.
Neurobiologist Michael Greenberg, PhD, and geneticist David E. Reich, PhD, both at Harvard Medical School, will co-lead the Center. The agenda is a bold one: to catalogue the key genes required for human brain evolution, to analyze their roles in human behavior and cognition and to study their functions to discover evolutionary mechanisms.
An evolving understanding
We already know some basics of human brain evolution. First came the enlargement of the primate brain, culminating perhaps 2 million years ago with the emergence of our genus, Homo, and the use of crude stone tools and fire. Next came a tripling of brain size during the 500,000 years before Homo sapiens arose. Finally, just over 50,000 years ago, there was a great leap forward in human behavior, with archaeological evidence of more efficient manufacturing of stone tools and a rich aesthetic and spiritual life.
What transpired genetically? Prior research has taken a piecemeal approach to occasional genes that have different structures in humans versus non-humans. For example, Walsh’s lab has identified several genes regulating cerebral cortical size and patterning, some of them through the study of brain abnormalities. (The lab recently found a gene involved in brain folding — thanks to a brain malformation called polymicrogyria — that may have enhanced our language ability.)
But such findings only scratch the surface of the cognitive, behavioral and cultural strides we humans have made over the past 50,000 years. That’s a blink of the eye in evolutionary terms. What enabled us to invent money, develop agriculture, build factories, write symphonies, tell jokes?
Rosetta stone(s) to decode brain evolution
The researchers think not one but multiple mechanisms of evolution helped form the modern human brain. Such mechanisms include:
- gene addition, duplication or deletion
- alteration in the protein-coding sequence of genes to create new or modified biochemical functions
- changes in noncoding DNA sequences altering patterns of gene expression — allowing an existing gene to be “re-purposed.”
- polygenic changes — changes in many genes working together.
Accordingly, the Center’s research methods will include, in varying combinations:
- sequencing of ancient DNA recovered from bones and teeth
- genomic studies of large populations to identify regions that correlate with human traits
- genetic studies to test functional effects of mutations in the evolutionarily important genomic sequences
- functional studies in neurons to determine the roles of these evolutionarily important sequences in the brain.
No genetic stone unturned
All these approaches will be supported by powerful computational data analysis — reaching across genomes, across populations, across hundreds of thousands of years.
The project leaders sum it up: “This group will provide the most rigorous possible examination of how, when and where the unique features of the amazing human brain came about.”