The uniqueness of human beings vis-à-vis other species can be attributed to the human brain. Undoubtedly so. This has been strongly established through extensive studies exploring the differences between the human brain and those of other related mammals. But even with the best of efforts, the comparisons have only been versions of apples and oranges. Now, D Svante Paabo’s laboratory has found a unique way of finding the answer. They have decided to study the modern human brain vis-à-vis the brains of their closest known relatives, the Neanderthal brains. After all, one species thrived while the other perished despite their similarities. The answer could lie in the brain development of the two species. The obvious question is “how”.
This is where it gets really interesting. Dr Paabo’s lab will be using cutting-edge gene-editing technology (Clustered Regularly Interspaced Short Palindromic Repeats or CRISPR to be precise) to insert ‘Neanderthalised’ DNA in human stem cells and grow them into mini-brains, called brain-organoids.
The ethical questions of growing a human brain can quickly be dismissed since the current study clearly specifies that these organoids will be devoid of thoughts or feelings — they will actually just be masses of brain cells. They are only meant to replicate some basic structures of the adult brain.
The Neanderthal genome has been sequenced painstakingly by an international team Dr Paabo led. His subsequent work has seen the insertion of Neanderthal genes for craniofacial development in mice and Neanderthal pain reception genes into frog eggs. These studies sought to study the difference Neanderthal genes would have in craniofacial development or pain threshold of other species. Though these studies did offer some insights, the availability of new technology of gene-editing and other major scientific developments have led the team to delve right into human brain cells to seek answers that make modern human beings who we are today.
This will be a very interesting study, considering that studies by Dr Paabo’s group have revealed that Neanderthals were more advanced than they were given credit for in the past. It is also known that they had a larger brain size compared to that of modern human beings. Their fate, therefore, is a little more perplexing. Dr Paabo suspects that the answer could be in their brain’s cognitive abilities; else, it could be something that still needs to be discovered.
Coming to the designing of the experiments, Dr Paabo’s group will, for now, centre their studies around three genes crucial for brain development. Human stem cells (normal as well as the Neanderthalised ones) will be subjected to chemical triggers which will make them neurons. As the cells divide and re-divide, they essentially become a clump of neurons without any definite organised structure. The idea is to study the human neuronal clumps vis-a-vis the Neanderthalised ones and try and determine the differences in the rate and process of development, differences in the neuronal synapses and electrical activity. As of now, any difference in the above-mentioned parameters that can be established will only indicate how the brain development was different in between the two lineages. An answer to the difference in the fates of the two lineages will have to wait.
Human evolution has always been a subject of curiosity and intrigue. Biological sciences have just been armed with tools and techniques that enable us to look deeper into ourselves. This study is only one such example. However, as with all techniques that have the ability to shape the future, this study is also fraught with ethical concerns, and rightly so. The foundation that is being laid with this study can truly test the limits of what is permissible by ethical standards and what is not. But as of now, ethical questions can wait.