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Evolutionary Trends in Human Populations

Exploring the unique physiological traits of the Sama-Bajau free-divers, known as 'Sea Nomads', who have developed larger spleens for extended underwater dives. The text delves into recent human evolutionary genetics, revealing rapid changes in traits like lactase persistence and pigmentation. It also discusses the pace of human genetic diversification, ongoing natural selection in societies, modern medicine's influence on evolution, and the impact of education and lifestyle on human evolution.

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1

Role of spleen in mammalian dive reflex

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Spleen contracts to release oxygen-rich red blood cells during dives, extending submersion time.

2

Natural selection in Sama-Bajau

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Favors individuals with larger spleens for prolonged diving capability.

3

Potential for further evolutionary developments in Sama-Bajau

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Continuous free-diving lifestyle may lead to more physiological adaptations over time.

4

Geneticists have used ______ to observe recent human evolutionary changes by analyzing ______.

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genomic science single nucleotide polymorphisms (SNPs)

5

Research has shown that in the last ______ years, the British population experienced notable shifts in ______ and ______.

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two thousand lactase persistence pigmentation

6

Traits such as ______ stature, larger ______ volume, and broader ______ width have been favored by natural selection.

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increased cranial pelvic

7

Although less definitive, evidence suggests selection on ______ traits, indicating ongoing ______ pressures in humans.

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polygenic evolutionary

8

Impact of population growth on genetic variants

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Rapid growth in last 5-10k years increased genetic variation.

9

Mutation load difference between European and African Americans

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European Americans have higher mutation load due to Out-of-Africa bottleneck.

10

Relationship between genetic mutations and disease prevalence

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More mutations don't equal higher disease rates; multiple changes often needed for disease.

11

In ______, individuals have developed a resistance to malaria within 20 generations.

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Cape Verde

12

Traits such as the timing of first childbirth, ______, and reproductive lifespan are still evolving.

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body size

13

In the ______, a preference for taller men has influenced sexual selection over the last 150 years.

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Netherlands

14

Different societal preferences have affected ______ in various cultures.

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reproductive success

15

The onset age for ______ is being postponed in humans.

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menopause

16

Certain populations are experiencing evolutionary changes in cardiovascular traits, such as ______ and blood pressure.

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cholesterol levels

17

Impact of C-sections on evolutionary dynamics

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C-sections may lead to more fetopelvic disproportion due to less natural selection on head size and pelvic width.

18

Factors influencing C-section rates

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Diabetes, obesity, and cultural/healthcare practices contribute to the varying prevalence of C-sections.

19

Dietary influence on genetic adaptations

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High-salt Western diet may drive genetic changes that protect against hypertension and hypercholesterolemia.

20

Recent ______ studies show evolutionary changes in ______ human generations.

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genomic current

21

In ______, a gene variant related to ______ addiction is less common, indicating selection against heavy smokers.

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Britain smoking

22

Genes linked to ______ diseases, such as ______, are becoming less frequent.

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late-onset Alzheimer's

23

Traits promoting increased ______ expectancy, like later ______ and postponed first childbirth, are on the rise.

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life puberty

24

These findings support the idea that ______ selection continues to influence ______ populations significantly.

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natural human

25

Height's influence on reproductive success

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Taller men and shorter women have more children; height is polygenic, so population height remains balanced.

26

Effect of higher education on childbirth timing

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Women with higher education levels who delay childbirth tend to have fewer children, potentially affecting future genetic makeup.

27

Genetic factors associated with longevity

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Genes promoting delayed puberty and reproduction are common in individuals with longer lifespans, impacting human evolution.

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Unique Physiological Traits of the Sama-Bajau Free-Divers

The Sama-Bajau people, often referred to as "Sea Nomads," have cultivated extraordinary physiological traits to adapt to their free-diving lifestyle. These adaptations have evolved over thousands of years, with natural selection favoring those with larger spleens. The spleen plays a crucial role in the mammalian dive reflex, where it contracts during underwater dives to release a reserve of oxygen-rich red blood cells, thus extending the time a diver can spend submerged. This adaptation is not found in agricultural or less aquatic societies, where such traits offer no particular advantage. The Sama-Bajau's continued reliance on free-diving suggests potential for further evolutionary developments in their physiology.
Sama-Bajau divers diving among vibrant corals, with wooden fins and traditional equipment, in crystal clear waters under a clear sky.

Progress in Human Evolutionary Genetics

Recent advancements in genomic science have enabled geneticists to detect subtle changes in human evolution over recent history. By examining single nucleotide polymorphisms (SNPs), researchers have identified rapid changes in allele frequencies that affect traits such as lactase persistence and pigmentation. Studies in the British population have shown significant shifts in these traits over the last two thousand years. Additionally, natural selection appears to have favored polygenic traits like increased stature, larger cranial volume, and broader pelvic width. While the evidence for selection on polygenic traits is less definitive than for monogenic traits, it nonetheless indicates ongoing evolutionary pressures in human populations.

The Pace of Human Genetic Diversification

The vast majority of single nucleotide variants in the human genome have arisen in the last 5,000 to 10,000 years, a period marked by rapid population growth and increased genetic variation. Some of these variants are deleterious, with European Americans showing a higher mutation load than African Americans, likely due to a bottleneck effect during the Out-of-Africa migration. Despite the rise in potentially harmful mutations, the prevalence of disease is not necessarily higher, as many conditions require multiple genetic changes to manifest. The current breadth of human genetic diversity suggests that our species is more capable of evolutionary change now than in the past, with natural selection possibly becoming more pronounced as populations expand.

Ongoing Natural Selection in Human Societies

Modern medicine and lifestyle changes have not halted the process of natural selection in humans. For example, the inhabitants of Cape Verde have developed resistance to malaria in just 20 generations. Traits such as the timing of first childbirth, body size, and length of reproductive life continue to evolve. In the Netherlands, sexual selection has favored taller men over the past century and a half, while in other societies, different preferences have influenced reproductive success. Additionally, the age of onset for menopause is being delayed, and cardiovascular traits like cholesterol levels and blood pressure are evolving in certain populations.

Modern Medicine's Influence on Human Evolution

While modern medicine has dramatically reduced infant mortality and increased lifespan, it has also allowed for the persistence of traits that might otherwise be selected against. The increasing prevalence of Cesarean sections (C-sections) has impacted the evolutionary dynamics of head size and pelvic width, potentially leading to more cases of fetopelvic disproportion. Cultural and health factors, such as the prevalence of diabetes and obesity, also affect C-section rates. Moreover, the high-salt Western diet has created selective pressures that may lead to genetic adaptations against hypertension and hypercholesterolemia.

Evolutionary Trends in Contemporary Human Populations

Large-scale genomic studies have uncovered evidence of evolutionary changes within current human generations. In Britain, for instance, an allele linked to smoking addiction has decreased in frequency, suggesting a selection against heavy smokers. Similarly, alleles associated with late-onset diseases like Alzheimer's are declining. Traits that contribute to a longer life expectancy, such as later puberty and delayed age at first birth, are becoming more prevalent. These observations confirm that natural selection remains a significant force in shaping human populations, even amidst modern societal influences.

Education, Lifestyle, and Human Evolution

Research in evolutionary genetics has highlighted the role of education and lifestyle in influencing reproductive success and longevity. For example, taller men and shorter women have been found to have more children, but since height is a polygenic trait, the overall population height is likely to remain balanced. Women with higher education levels who delay childbirth tend to have more children, which may influence the genetic makeup of future generations. Additionally, genetic factors that promote longevity, such as delayed puberty and reproduction, are more common among individuals with extended lifespans. These findings illustrate the intricate relationship between genetics, education, and lifestyle in the ongoing evolution of humans.