The following is an excerpt from “Human Life and Migration - an Origin Story,” (2020)

It is now commonly accepted that human life originated in East Africa. There is less agreement as to whether the humans that left Africa in a final exodus as recently as 100,000 years ago replaced all other hominids (thus becoming ancestors to everyone now alive) or humans evolved independently in geographically separated regions. Recently, the replacement scenario, as it is sometimes called, has been lent support from genetic research.

Genetic investigations into the origins of human life most often focus on mitochondrial DNA. As opposed to nuclear DNA, mitochondrial DNA is transmitted only from the mother. This allows for the tracing of mutations that arise independently of changes that occur because of the combining of the mother’s and father’s DNA. As useful as this is, the high mutation rate of mitochondrial DNA allows scientists a look at only relatively recent prehistory. Nuclear DNA, on the other hand, has a low mutation rate, making it ideal for looking into the more distant past. Studying the nuclear DNA of fossils now shows a substantial decrease in population size in Europe and Asia approximately 50—80 thousand years ago. No such decrease happened in Africa. This supports the idea that migrants from Africa replaced all previous humans, and did not interbreed with earlier migrants.

Other research shows less genetic diversity the farther human populations are located from Africa. This difference in diversity, which continues to the present day, also supports the hypothesis that modern human life came from Africa and gradually spread throughout the world. It is worth noting that there is no discontinuity in the decrease of diversity as one travels from Africa; this points to less distinct ethnic and racial divisions than is popularly thought to be the case.

The following is an excerpt from Night and Day, a novel by Virginia Woolf that was first published in 1919. The novel tells the story of two main female characters in London in the early 20th century.

It was a Sunday evening in October, and in common with many other young ladies of her class, Katharine Hilbery was pouring out tea. Perhaps a fifth part of her mind was thus occupied, and the remaining parts leapt over the little barrier of day which interposed between Monday morning and this rather subdued moment, and played with the things one does voluntarily and normally in the daylight. But although she was silent, she was evidently mistress of a situation which was familiar enough to her, and inclined to let it take its way for the six hundredth time, perhaps, without bringing into play any of her unoccupied faculties. A single glance was enough to show that Mrs. Hilbery was so rich in the gifts which make tea-parties of elderly distinguished people successful, that she scarcely needed any help from her daughter, provided that the tiresome business of teacups and bread and butter was discharged for her. 

Considering that the little party had been seated round the tea-table for less than twenty minutes, the animation observable on their faces, and the amount of sound they were producing collectively, were very creditable to the hostess. It suddenly came into Katharine’s mind that if someone opened the door at this moment he would think that they were enjoying themselves; he would think, “What an extremely nice house to come into!” and instinctively she laughed, and said something to increase the noise, for the credit of the house presumably, since she herself had not been feeling exhilarated. At the very same moment, rather to her amusement, the door was flung open, and a young man entered the room. Katharine, as she shook hands with him, asked him, in her own mind, “Now, do you think we’re enjoying ourselves enormously?”... “Mr. Denham, mother,” she said aloud, for she saw that her mother had forgotten his name.

The following is an excerpt from Agnes Grey, an autobiographical novel by Anne Bronte that follows the life of a governess working in wealthy British households in the 19th century.

To avoid trouble and confusion, I have taken my pupils one by one, and discussed their various qualities; but this can give no adequate idea of being worried by the whole three together; when, as was often the case, all were determined to ‘be naughty, and to tease Miss Grey, and put her in a passion.’ 

Sometimes, on such occasions, the thought has suddenly occurred to me—’If they could see me now!’ meaning, of course, my friends at home; and the idea of how they would pity me has made me pity myself—so greatly that I have had the utmost difficulty to restrain my tears: but I have restrained them, till my little tormentors were gone to dessert, or cleared off to bed (my only prospects of deliverance), and then, in all the bliss of solitude, I have given myself up to the luxury of an unrestricted burst of weeping. But this was a weakness I did not often indulge: my employments were too numerous, my leisure moments too precious, to admit of much time being given to fruitless lamentations.

The following is an excerpt from “Human Life and Migration - an Origin Story,” (2020)

It is now commonly accepted that human life originated in East Africa. There is less agreement as to whether the humans that left Africa in a final exodus as recently as 100,000 years ago replaced all other hominids (thus becoming ancestors to everyone now alive) or humans evolved independently in geographically separated regions. Recently, the replacement scenario, as it is sometimes called, has been lent support from genetic research.

Genetic investigations into the origins of human life most often focus on mitochondrial DNA. As opposed to nuclear DNA, mitochondrial DNA is transmitted only from the mother. This allows for the tracing of mutations that arise independently of changes that occur because of the combining of the mother’s and father’s DNA. As useful as this is, the high mutation rate of mitochondrial DNA allows scientists a look at only relatively recent prehistory. Nuclear DNA, on the other hand, has a low mutation rate, making it ideal for looking into the more distant past. Studying the nuclear DNA of fossils now shows a substantial decrease in population size in Europe and Asia approximately 50—80 thousand years ago. No such decrease happened in Africa. This supports the idea that migrants from Africa replaced all previous humans, and did not interbreed with earlier migrants.

Other research shows less genetic diversity the farther human populations are located from Africa. This difference in diversity, which continues to the present day, also supports the hypothesis that modern human life came from Africa and gradually spread throughout the world. It is worth noting that there is no discontinuity in the decrease of diversity as one travels from Africa; this points to less distinct ethnic and racial divisions than is popularly thought to be the case.

The following is an excerpt from Night and Day, a novel by Virginia Woolf that was first published in 1919. The novel tells the story of two main female characters in London in the early 20th century.

It was a Sunday evening in October, and in common with many other young ladies of her class, Katharine Hilbery was pouring out tea. Perhaps a fifth part of her mind was thus occupied, and the remaining parts leapt over the little barrier of day which interposed between Monday morning and this rather subdued moment, and played with the things one does voluntarily and normally in the daylight. But although she was silent, she was evidently mistress of a situation which was familiar enough to her, and inclined to let it take its way for the six hundredth time, perhaps, without bringing into play any of her unoccupied faculties. A single glance was enough to show that Mrs. Hilbery was so rich in the gifts which make tea-parties of elderly distinguished people successful, that she scarcely needed any help from her daughter, provided that the tiresome business of teacups and bread and butter was discharged for her.

The following passage is adapted from Ricki Lewis, "Did Donkeys Arise from an Inverted Chromosome?", originally published 2018 in PLOSOne Blogs.

In the world of genome sequencing, donkeys haven’t received nearly as much attention as horses. But now a report on a new-and-improved genome sequence of Willy, a donkey (Equus asinus) jack 5 born at the Copenhagen Zoo in 1997, appears in the new issue of Science Advances, from Gabriel Renaud, of the Centre for GeoGenetics, Natural History Museum of Denmark. (A female is a jenny or jennet.) The new view provides clues to how donkeys may have branched from horses along the tree of evolution.

Horses and their relatives, past and present, are genetically peculiar in that their chromosomes are rearranged, with respect to each other. That should  prevent them from producing viable hybrids – yet they do. Donkeys have 62 chromosomes and horses have 64. A mule comes from the mating of a male donkey and a female horse, and has 63 chromosomes. Mules are known for their  intelligence, calm, stamina, and persistence. Their horse-like bodies perched on donkey-like limbs make them ideal for hauling tourists around the Grand Canyon and schlepping supplies in combat situations. The ears are large like those of the horse mom, and mules make a sound that begins as a whinny and becomes a bray.

The complementary couple, a female donkey and a male horse, produces a hinny, smaller than a mule. Hinnies are the flip side of the mule, with a donkey’s physique atop horsey limbs, and short donkey ears. They’re rarer than mules, but also have 63 chromosomes. It’s easy to mix them up.

Comparing Willy’s genome to a horse genome revealed their close evolutionary relationship. Only about 15% of horse genes aren’t also in the donkey genome, and only about 10% of a donkey’s genes don’t have counterparts in the horse. Most of the genes that they share provide basic “housekeeping” functions like dismantling proteins, repairing DNA, enabling embryonic development, and controlling cell division. So that’s why a copy of each genome can smush together to yield mules and hinnies.

A second form of information encoded in genomes, in addition to the A, C, T, G sequence, is the pattern of whether the two variants of individual genes are different (heterozygous) or the same (homozygous). Many contiguous homozygous genes form a “run of homozygosity” (ROH).

An ROH indicates a chromosome chunk, perhaps as long as millions of DNA bases, that’s the same from each of an individual’s parents, who in turn inherited it from a shared ancestor, like a grandparent that cousins share. The longer the ROH, the more recent the shared ancestor, because it takes time for mutations to accrue that would break the sameness of the sequence.

Scrutinizing ROHs can reveal recent inbreeding and domestication, help to reconstruct possible branching patterns of evolution, and, more practically, help ancestry companies assign the DNA in spit samples to geographic areas where people’s ancestors might have come from. The new study compared ROHs for the three zebra and three ass species, confirming that Willy’s most recent ancestors were Somali wild asses.

The researchers used Chicago HiRise assembly technology to up the quality of Willy’s genome sequence. “This new assembly allowed us to identify fine chromosomal rearrangements between the horse and the donkey that likely played an active role in their divergence and, ultimately, speciation,” they write.

The bigger pieces enabled them to zero in on DNA sequences where chromosomes contort, such as inversions (where a sequence flips) or translocations (where different chromosome types exchange parts). These events could have fueled the reproductive isolation of small populations that can expand into speciation.

If eventually sperm with one inverted chromosome fertilized eggs with the same inversion, animals would have been conceived in which both copies of the chromosome are inverted – and they’d be fertile with each other, but not with horses. Once a subpopulation with the inversion became established, further genetic changes would separate them further from the ancestral horse.

Passage 1 is adapted from Emma Hart Willard, "Improving Female Education." Originally published in 1819.

If the improvement of the American female character, and that alone, could be affected by public liberality, employed in giving better means of instruction; such improvement of one half of society, and that half, which barbarous and despotic nations have ever degraded, would of itself be an object, worthy of the most liberal government on earth; but if the female character be raised, it must inevitably raise that of the other sex; and thus does the plan proposed, offer, as the object of legislative bounty, to elevate the whole character of the community.

As evidence that this statement does not exaggerate the female influence in society, our sex needs but be considered, in the single relation of mothers. In this character, we have the charge of the whole mass of individuals, who are to compose the succeeding generation; during that period of youth, when the pliant mind takes any direction, to which it is steadily guided by a forming hand. How important a power is given by this charge! yet, little do too many of my sex know-how, either to appreciate or improve it. Unprovided with the means of acquiring that knowledge, which flows liberally to the other sex- having our time of education devoted to frivolous acquirements, how should we understand the nature of the mind, so as to be aware of the importance of those early impressions, which we make upon the minds of our children? -or how should we be able to form enlarged and correct views, either of the character, to which we ought to mold them, or of the means most proper to form them aright?

Considered in this point of view, were the interests of male education alone to be consulted, that of females becomes of sufficient importance to engage the public attention. Would we rear the human plant to its perfection, we must first fertilize the soil which produces it. If it acquire its first bent and texture upon a barren plain, it will avail comparatively little, should it be afterwards transplanted to a garden.

Passage 1 is adapted from Emma Hart Willard, "Improving Female Education." Originally published in 1819.

If the improvement of the American female character, and that alone, could be affected by public liberality, employed in giving better means of instruction; such improvement of one half of society, and that half, which barbarous and despotic nations have ever degraded, would of itself be an object, worthy of the most liberal government on earth; but if the female character be raised, it must inevitably raise that of the other sex; and thus does the plan proposed, offer, as the object of legislative bounty, to elevate the whole character of the community.

As evidence that this statement does not exaggerate the female influence in society, our sex needs but be considered, in the single relation of mothers. In this character, we have the charge of the whole mass of individuals, who are to compose the succeeding generation; during that period of youth, when the pliant mind takes any direction, to which it is steadily guided by a forming hand. How important a power is given by this charge! yet, little do too many of my sex know-how, either to appreciate or improve it. Unprovided with the means of acquiring that knowledge, which flows liberally to the other sex- having our time of education devoted to frivolous acquirements, how should we understand the nature of the mind, so as to be aware of the importance of those early impressions, which we make upon the minds of our children? -or how should we be able to form enlarged and correct views, either of the character, to which we ought to mold them, or of the means most proper to form them aright?

Considered in this point of view, were the interests of male education alone to be consulted, that of females becomes of sufficient importance to engage the public attention. Would we rear the human plant to its perfection, we must first fertilize the soil which produces it. If it acquire its first bent and texture upon a barren plain, it will avail comparatively little, should it be afterwards transplanted to a garden.

Passage 2 is adapted from Benjamin Rush, "Thoughts upon Female Education". Originally published 1787.

A philosopher once said, "let me make all the ballads of a country and I care not who makes its laws." He might with more propriety have said, let the ladies of a country be educated properly, and they will not only make and administer its laws, but form its manners and character. It would require a lively imagination to describe, or even to comprehend, the happiness of a country where knowledge and virtue were generally diffused among the female sex. Our young men would then be restrained from vice by the terror of being banished from their company. The loud laugh and the malignant smile, at the expense of innocence or of personal infirmities– the feats of successful mimicry and the low priced wit which is borrowed from a misapplication of scripture phrases– would no more be considered as recommendations to the society of the ladies. A double-entendre in their presence would then exclude a gentleman forever from the company of both sexes and probably oblige him to seek an asylum from contempt in a foreign country.

If I am wrong in those opinions in which I have taken the liberty of departing from the general and fashionable habits of thinking I am sure you will discover and pardon my mistakes. But if I am right, I am equally sure you will adopt my opinions for to enlightened minds truth is alike acceptable, whether it comes from the lips of age or the hand of antiquity or whether it be obtruded by a person who has no other claim to attention than a desire of adding to the stock of human happiness.

To you, young ladies, an important problem is committed for solution: whether our present plan of education be a wise one and whether it be calculated to prepare you for the duties of social and domestic life. I know that the elevation of the female mind, by means of moral, physical, and religious truth, is considered by some men as unfriendly to the domestic character of a woman. But this is the prejudice of little minds and springs from the same spirit which opposes the general diffusion of knowledge among the citizens of our republics. If men believe that ignorance is favorable to the government of the female sex, they are certainly deceived, for a weak and ignorant woman will always be governed with the greatest difficulty. It will be in your power ladies, to correct the mistakes and practice of our sex upon these subjects by demonstrating that the female temper can only be governed by reason and that the cultivation of reason in women is alike friendly to the order of nature and to private as well as public happiness.

The following passage and corresponding figure are from Emilie Reas. "How the brain learns to read: development of the “word form area”", PLOS Neuro Community, 2018.

The ability to recognize, process and interpret written language is a uniquely human skill that is acquired with remarkable ease at a young age. But as anyone who has attempted to learn a new language will attest, the brain isn’t “hardwired” to understand written language. In fact, it remains somewhat of a mystery how the brain develops this specialized ability. Although researchers have identified brain regions that process written words, how this selectivity for language develops isn’t entirely clear. 

Earlier studies have shown that the ventral visual cortex supports recognition of an array of visual stimuli, including objects, faces, and places. Within this area, a subregion in the left hemisphere known as the “visual word form area” (VWFA) shows a particular selectivity for written words. However, this region is characteristically plastic. It’s been proposed that stimuli compete for representation in this malleable area, such that “winner takes all” depending on the strongest input. That is, how a site is ultimately mapped is dependent on what it’s used for in early childhood. But this idea has yet to be confirmed, and the evolution of specialized brain areas for reading in children is still poorly understood.

In their study, Dehaene-Lambertz and colleagues monitored the reading abilities and brain changes of ten six-year-old children to track the emergence of word specialization during a critical development period. Over the course of their first school-year, children were assessed every two months with reading evaluations and functional MRI while viewing words and non-word images (houses, objects, faces, bodies). As expected, reading ability improved over the year of first grade, as demonstrated by increased reading speed, word span, and phoneme knowledge, among other measures.

Even at this young age, when reading ability was newly acquired, words evoked widespread left-lateralized brain activation. This activity increased over the year of school, with the greatest boost occurring after just the first few months. Importantly, there were no similar activation increases in response to other stimuli, confirming that these adaptations were specific to reading ability, not a general effect of development or education. Immediately after school began, the brain volume specialized for reading also significantly increased. Furthermore, reading speed was associated with greater activity, particularly in the VWFA. The researchers found that activation patterns to words became more reliable with learning. In contrast, the patterns for other categories remained stable, with the exception of numbers, which may reflect specialization for symbols (words and numbers) generally, or correlation with the simultaneous development of mathematics skills.

What predisposes one brain region over another to take on this specialized role for reading words? Before school, there was no strong preference for any other category in regions that would later become word-responsive. However, brain areas that were destined to remain “non-word” regions showed more stable responses to non-word stimuli even before learning to read. Thus, perhaps the brain takes advantage of unoccupied real-estate to perform the newly acquired skill of reading.

These findings add a critical piece to the puzzle of how reading skills are acquired in the developing child brain. Though it was already known that reading recruits a specialized brain region for words, this study reveals that this occurs without changing the organization of areas already specialized for other functions. The authors propose an elegant model for the developmental brain changes underlying reading skill acquisition. In the illiterate child, there are adjacent columns or patches of cortex either tuned to a specific category, or not yet assigned a function. With literacy, the free subregions become tuned to words, while the previously specialized subregions remain stable.

The rapid emergence of the word area after just a brief learning period highlights the remarkable plasticity of the developing cortex. In individuals who become literate as adults, the same VWFA is present. However, in contrast to children, the relation between reading speed and activation in this area is weaker in adults, and a single adult case-study by the authors showed a much slower, gradual development of the VWFA over a prolonged learning period of several months. Whatever the reason, this region appears primed to rapidly adopt novel representations of symbolic words, and this priming may peak at a specific period in childhood. This finding underscores the importance of a strong education in youth. The authors surmise that “the success of education might also rely on the right timing to benefit from the highest neural plasticity. Our results might also explain why numerous academic curricula, even in ancient civilizations, propose to teach reading around seven years.”

The figure below shows different skills mapped to different sites in the brain before schooling and then with and without school. Labile sites refer to sites that are not currently mapped to a particular skill.

The following passage is adapted from Ricki Lewis, "Did Donkeys Arise from an Inverted Chromosome?", originally published 2018 in PLOSOne Blogs.

In the world of genome sequencing, donkeys haven’t received nearly as much attention as horses. But now a report on a new-and-improved genome sequence of Willy, a donkey (Equus asinus) jack 5 born at the Copenhagen Zoo in 1997, appears in the new issue of Science Advances, from Gabriel Renaud, of the Centre for GeoGenetics, Natural History Museum of Denmark. (A female is a jenny or jennet.) The new view provides clues to how donkeys may have branched from horses along the tree of evolution.

Horses and their relatives, past and present, are genetically peculiar in that their chromosomes are rearranged, with respect to each other. That should prevent them from producing viable hybrids – yet they do. Donkeys have 62 chromosomes and horses have 64. A mule comes from the mating of a male donkey and a female horse and has 63 chromosomes. Mules are known for their intelligence, calm, stamina, and persistence. Their horse-like bodies perched on donkey-like limbs make them ideal for hauling tourists around the Grand Canyon and schlepping supplies in combat situations. The ears are large like those of the horse mom, and mules make a sound that begins as a whinny and becomes a bray.

The complementary couple, a female donkey and a male horse, produces a hinny, smaller than a mule. Hinnies are the flip side of the mule, with a donkey’s physique atop horsey limbs, and short donkey ears. They’re rarer than mules but also have 63 chromosomes. It’s easy to mix them up.

Comparing Willy’s genome to a horse genome revealed their close evolutionary relationship. Only about 15% of horse genes aren’t also in the donkey genome, and only about 10% of a donkey’s genes don’t have counterparts in the horse. Most of the genes that they share provide basic “housekeeping” functions like dismantling proteins, repairing DNA, enabling embryonic development, and controlling cell division. So that’s why a copy of each genome can smush together to yield mules and hinnies.

The second form of information encoded in genomes, in addition to the A, C, T, G sequence, is the pattern of whether the two variants of individual genes are different (heterozygous) or the same (homozygous). Many contiguous homozygous genes form a “run of homozygosity” (ROH).

An ROH indicates a chromosome chunk, perhaps as long as millions of DNA bases, that’s the same from each of an individual’s parents, who in turn inherited it from a shared ancestor, like a grandparent that cousins share. The longer the ROH, the more recent the shared ancestor, because it takes time for mutations to accrue that would break the sameness of the sequence.

Scrutinizing ROHs can reveal recent inbreeding and domestication, help to reconstruct possible branching patterns of evolution, and, more practically, help ancestry companies assign the DNA in spit samples to geographic areas where people’s ancestors might have come from. The new study compared ROHs for the three zebra and three ass species, confirming that Willy’s most recent ancestors were Somali wild asses.

The researchers used the Chicago HiRise assembly technology to up the quality of Willy’s genome sequence. “This new assembly allowed us to identify fine chromosomal rearrangements between the horse and the donkey that likely played an active role in their divergence and, ultimately, speciation,” they write.

The bigger pieces enabled them to zero in on DNA sequences where chromosomes contort, such as inversions (where a sequence flips) or translocations (where different chromosome types exchange parts). These events could have fueled the reproductive isolation of small populations that can expand into speciation.

If eventually, sperm with one inverted chromosome fertilized eggs with the same inversion, animals would have been conceived in which both copies of the chromosome are inverted – and they’d be fertile with each other, but not with horses. Once a subpopulation with the inversion became established, further genetic changes would separate them further from the ancestral horse.