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Determine percentage of crow hybrids

Determine percentage of crow hybrids


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We had in class following question which I had no idea how to get to the correct answer:

The carrion crow and the hooded crow are fertile together, but their reproductive success is reduced by 50%. In a certain region exist two populations of both species of roughly the same size. Thus, mixed couples occur in about 10% of all cases. What is the percentage of hybrids in the F1-generation?

(Translated from German.)

I thought it would be something like 5/95 = 5,3% but apparently the answer is 1%. Why?


In order to make your reasoning clearer, you should use more formal notations and explain your thinking step by step. Here's a proposition.

Let's use the following notations :

  • $C$: the total number of couples (mixed and not mixed)
  • $r$: the reproductive success
  • $F1_h$: the number of hybrids in the F1 generation
  • $F1_{nh}$: the number of non hybrids in the F1 generation

You are looking for the percentage of hydrids in the F1 generation, which is: $x = frac{F1_h}{F1_h + F1_{nh}}$

You know that $10~\%$ of the couples are mixed couples and that their reproductive success is reduced by $50~\%$. This can be written: $egin{cases} 0.9cdot C cdot r = F1_{nh} 0.1cdot Ccdot frac{r}{2} = F1_h end{cases}$

Thus: $displaystyle x = frac{F1_h}{F1_h + F1_{nh}} = frac{0.05cdot Ccdot r}{Ccdot rcdot 0.95} = frac{0.05}{0.95}$

This is indeed the result you suggested. So the correction you were given might not be correct. Or maybe there was some more information in your homework that you ignored…


Risk assessment by crow phenotypes in a hybrid zone

Predation is one of the most selective forces in evolution and, thus, predation may select against hybrids in narrow hybrid zones. It may be possible that parental phenotypes and hybrids differ in their responses towards predators or humans. As predation is difficult to observe I used flight-initiation distance (FID) as a metric of risk assessment. FID is a measurable outcome of the trade-off between fleeing and remaining. Here, I tested whether hybrid and parent crow phenotypes (Corvus corone, Corvus cornix) from the hybrid zone in Eastern Germany differ in their FID. Further, I measured many environmental and social variables to control statistically for their influence on FID. I sampled 154 individuals (53 hooded crows, 54 carrion crows, and 48 hybrids) in the hybrid zone in eastern Germany. I calculated a general linear model using a stepwise backward procedure to establish a minimum model containing only significant variables that explained FID in crows. The variable phenotype (hooded, carrion, hybrid) was then added to the model. There were no differences in FID between hybrids and both parental phenotypes types, suggesting similar risk assessment. This suggests that hybrids may behave similarly in their decision to flee as their parent phenotypes, which, in turn, provides no evidence for a selective disadvantage. An additional analysis focusing on pure phenotypic flocks showed that hybrids in pure hybrid flocks had a lower FID than both parental species in pure flocks. This suggests that hybrids in pure hybrid flocks may be at a disadvantage.

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‘Human Monkey’ Hybrid Created for Research Reignites Debate on Cross-species Animals

Scientists associated with the Salk Institute in San Diego, California have injected primate embryos with human stem cells to create a new hybrid that continued to grow for up to 20 days but the scientific community is questioning the ethics of the moral status of the ‘monkey-human’ hybrid created by the scientists in the US and China, these embryos are to be used to help with knowledge on developmental biology and evolution and help in research for cancer treatments.

The idea behind creating the hybrids was that humans cannot be used for all experiments and so a nearly human creature can help solve the problem, said lead author Juan Carlos Izpisua Belmonte.

However, rival scientists have warned about the ethical implications of it, saying it raises questions if these embryos could have human-like faculties. Julian Savulesca, an expert in the ethics of scientific research at University of Oxford said, “The key ethical question is: what is the moral status of these novel creatures?" He also questioned whether these hybrids should be considered human enough that would determine one’s behavior towards them or if they actual have human like mental capacity and how correct it is to use them for research.

Cross-species chimeras (genetic chimerism or chimera is a single organism composed of cells with more than one distinct genotype) have been made by scientists since the past 4 decades with rodents. In this particular study, the scientists were able to create a way to allow the monkey embryos to stay alive and grow outside of the body. Six days after the creation, the embryos were injected with 25 human cells. After a day, human cells were detected in 132 embryos. After 10 days, out of the them, 103 of the chimeric embryos were still developing.

Harvard Scientists Are Trying to Resurrect the Woolly Mammoth Through Cloning. Is De-extinction Plausible?

The scientists observed that slowly most of their surviving rates declined and on the 19th day, only three of these chimeras were alive, whereupon they were destroyed.

This particular team had previously also tried to develop a human-pig hybrid earlier which didn’t last along with other hybrid experiments. With the new embryos, the percentage of human cells stayed high throughout the the 20 day period, scientists said.

“This will allow us to gain better insight into whether there are evolutionarily imposed barriers to chimera generation and if there are any means by which we can overcome them," Izpisua Belmonte was quoted as saying.


MATERIALS AND METHODS

Geographical distributions

Geographical distributions of Nuphar variegata, N. microphylla, and N. x rubrodisca were determined from 281 specimens examined from 15 herbaria (BM, DAO, FLAS, IA, MT, NASC, NHA, NCSC, P, TUFT, UC, UNA, US, V, VT). The geographical locality of each specimen was plotted on North American base maps to obtain estimates of the distribution ranges for each taxon (see Appendix 1 for citation of representative specimens).

Morphological analysis

Morphological data were obtained from 216 of the herbarium specimens examined for geographical distributions (Appendix 1). Five vegetative and ten reproductive characters were scored for 77 operational taxonomic units (OTUs) of Nuphar microphylla, 69 OTUs of N. × rubrodisca, and 70 OTUs of N. variegata. For each taxon, means and standard deviations were calculated for all variables using SYSTAT (version 5.0) software (Wilkinson, 1990). Character means were compared among the three taxa using an analysis of variance (ANOVA) and were evaluated for significant differences by performing a Tukey HSD post hoc test. Data were then arranged in a rectangular matrix for input in principal components analyses (PCA). Unscorable data were treated as missing. The matrix included OTUs of N. microphylla, N. variegata, and N. × rubrodisca (216 OTUs × 15 characters 52% missing data). The PCA was performed using NTSYS-pc (version 1.80) software (Rohlf, 1993). Data were standardized by dividing the difference of each variable and its mean by the standard deviation. Product moment correlations were computed among the standardized variables, the first three principal component axes were extracted from the correlation matrix, and OTUs were projected upon each axis. Results of the PCA were depicted as a scatterplot representing the superimposition of components I and II. The percentage variation explained by each eigenvalue and correlations of variables with eigenvectors were tabulated.

Pollen viability analysis

Pollen viability from 30 accessions (ten of each taxon) was estimated from the percentage stainability of 100+ randomly selected grains taken from herbarium specimens (Appendix 2). Anthers were removed from herbarium sheets and dissected in aniline blue/lactophenol following Radford et al. (1974). Means (percentage viability) and standard deviations were calculated as above using SYSTAT. Differences among means were determined by ANOVA and Tukey tests as described above.

RAPD analysis

Total genomic DNA was extracted from young, submersed leaf tissue representing three accesssions of Nuphar microphylla, five accessions of N. × rubrodisca, and five accessions of N. variegata (Appendix 3) using a modified CTAB procedure (Doyle and Doyle, 1987). Amplifications were carried out in 25-μL reactions consisting of 10 mmol/L Tris-HCL (pH 8.3), 50 mmol/L KCl, 0.005% Tween 20, 0.005% NP-40, 2.0 mmol/L MgCl2, 100 μmol/L each of dATP, dCTP, dGTP, and dTTP, 15 ng of primer, 1 μL (∼20 ng) DNA, and 0.6 units of AmpliTaq DNA polymerase (Perkin-Elmer, Norwalk, Connecticut). Eight random 10-mer oligodeoxynucleotide primers (OPF-1, OPF-2, OPF-3, OPF-4, OPF-5, OPF-6, OPF-8, OPF-10 Operon Technologies, Alameda, California) were used to amplify DNAs (each reaction used a single primer). A thermocycle profile of 1 min at 94°C, 2 min at 36°C, and 2 min at 72°C was carried out for 45 cycles followed by a 7-min final extension cycle at 72°C.

Amplification products were separated electrophoretically on 1.5% agarose gels in 0.5x tris-borate-EDTA buffer and were visualized by staining with ethidium bromide. Band sizes were estimated using a standard marker consisting of BstE II-digested Lambda DNA. A preliminary screening was conducted that included several additional Nuphar species (N. japonica, N. lutea, N. advena, and N. polysepala) to identify RAPD markers specific for either N. microphylla or N. variegata. Non specific markers, as well as markers that occurred in all three taxa (N. microphylla, N. variegata, N. × rubrodisca), were excluded from the analysis. RAPD data were summarized as the number of markers shared by N. × rubrodisca and either N. microphylla or N. variegata. Band reproducibility was verified by comparing several replicated amplifications for each marker scored.


Monohybrid Corn Lab

A cross between individuals that involves one pair of contrasting traits is called a monohybrid cross. First we will use Punnett square diagrams to predict the results of various monohybrid crosses. We will then examine ears of corn Purple results from the dominant allele (P), and yellow from the recessive allele (p). We will be making observations and assumptions for both the genotype or genetic make-up, and the phenotype or external appearance.
Review genetics and the use of Punnett squares in a biology text before doing this experiment.

Appropriate ears of corn.
(You can purchase them from a biological supply, such as Carolina. You need a heterozygous X heterozygous 3:1, and a monohybrid test cross 1:1.)

Theoretical: We will use a Punnett square to examine the theoretical outcome of possible monohybrid crosses.

1. The first cross is with a Homozygous dominant parent (PP), and a Homozygous recessive parent (pp).
Fill in the Punnett square. Each box represents a genotype possibility for an offspring. Place the allele donated by each parent in the corresponding box. Now list the possible genotypes and their corresponding phenotype.
Remember: The genotype is represented by the two letters for the offspring, and the phenotype is a color.
Remember: If an individual’s genotype is heterozygous, the dominant trait will be expressed in the phenotype.
Give the percent possible for the phenotypes.


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Mendel’s Monohybrid Cross Experiment

In this article, we shall study Mendel’s monohybrid cross experiment and its conclusions.

The first scientific explanation of inheritance was given by Mendel in 1866. He performed a series of experiments on garden pea in a scientific manner and proposed rules. which are called as Mendel’s Laws of Inheritance. His work is known as Mendelism. He laid down a foundation of Genetics hence he is called Father of genetics.

Reasons for Selection of Garden Pea by Mendel:

  • Garden pea is an annual plant and completes the life cycle within three or four months. Due to this short lifespan, he was able to take three generations in a year.
  • It is a small herbaceous plant that produces many seeds and so he could grow thousands of pea plants in a small plot behind the church.
  • It is naturally self-pollinating and was available in the form of many varieties with contrasting characters. There were no intermediate characters.
  • Flowers are large enough for easy emasculation required for artificial cross and produce fertile offspring.

The Reason of Success of Mendel’s Experiment:

  • Mendel studied the inheritance of one character at a time whereas earlier scientists had considered the organism as a whole. Initially, Mendel considered the inheritance of one trait only. (Monohybrid). Then he studied two traits together (dihybrid) and then three (Trihybrid).
  • He started with pure line i.e. true breeding. He maintained a complete statistical record by counting an actual number of offspring.
  • He carried out experiments up to the second and third generations.
  • He conducted ample crosses and reciprocal crosses to eliminate chance.
  • He dealt with a large sample size.

Monohybrid Cross:

A cross between two pure (homozygous) patterns in which the inheritance pattern of only one of contrasting characters is studied is called monohybrid cross. It is a cross between two pure (obtained by true breeding) parents differing in a single pair of contrasting characters. The procedure is as follows:

Step – 1: Selection of parents and obtaining Pure lines:

He selected pure line plants by ensuring that the selected male (pure dwarf) and female parent plants (pure tall) are breeding true for the selected trait or traits by selfing them for three generations. Thus pure line plants are homozygous for a given trait.

Step – 2: Emasculation, Dusting and Raising F1 Generation (Hybridization):

Emasculation:

Emasculation is a process of removal of stamens before the formation of pollen grains (anthesis). This is done in the bud condition. The bud is carefully open and all stamens (9 + 1) are removed carefully. The stigma is protected against any foreign pollen with the help of a muslin bag.

Dusting and Raising F1 Generation:

The pollens from the selected male flowers are dusted on the stigma of an emasculated female flower. The cross-pollinated flowers were enclosed in separate bags (bagging) to avoid further deposition of pollens from another source. During the pollination, it was assured that the pollen is mature and the stigma is receptive. This is an artificial cross. Mendel crossed many flowers, collected seeds and raised F1 generation. The plants used as parents are said to represent parental generation and are designated as P1. The progeny obtained as a result of the crossing between parents is called the first filial (offspring) generation and is represented as F1. All plants of F1 generation were tall.

Punnett Square for F1 Generation:

T (tall) is a dominant character t (dwarf) is a recessive character.

Collection and Separation of Seeds:

Seeds were separated and collected in marked bottles. To study characters of seeds they are studied immediately but for other characters, seeds were sown to raise next generation (F2)of the plant.

Reciprocal Cross:

Mendel thought F1 Generation is tall because tallness character is given by female parent and dwarfness character is given by a male parent.

To counter check it he performed reciprocal cross. Now, He selected pure line plants by ensuring that the selected male (pure tall) and female parent plants (pure dwarf) are breeding true for the selected trait or traits by selfing them for three generations.

He got the same result as in the first case. From this, he concluded that tallness is a dominant character, while the dwarfness is the recessive character.

The plants obtained from the crossing of two individuals differing at least one set of characters are known as hybrids and the process of obtaining them is called hybridization.

Punnett Square for (Reciprocal Cross) F1 Generation:

T (tall) is a dominant character t (dwarf) is a recessive character.

Step – 3: Selfing of F1 hybrids to produce F2 Generation:

Mendel allowed natural pollination in each F1 hybrid collected seeds separately and F2 generation (second filial) is obtained. The ratio of tall plants to dwarf plants in F2 generation is found to be 3: 1

Punnett Square for F2 Generation:

T (tall) is a dominant character t (dwarf) is a recessive character.

The ratio of tall plants to dwarf plants was around 3:1. Thus phenotype ratio (tall : dwarf) is 3: 1. The genotype ratio (pure tall : hybrid tall : pure dwarf) is 1:2:1.

Step – 4: Self Breeding:

Mendel carried self-breeding among F2 generations and obtained F3, then F4 generations.

Checking With Other Traits:

Mendel performed monohybrid crosses and reciprocal crosses with all the seven pairs of contrasting characters separately and obtained similar results.

Only one of the two characters was expressed in F1 generation. In F2 generation the character which was shown in F1 generation was in large number and the other in small number and the ratio was found to be 3:1. This ratio is called the monohybrid ratio.

Genotype Ratio for Monohybrid Cross:

The ratio of pure dominant character to hybrid character to pure contrasting recessive character is called the genotype ratio. In monohybrid cross experiment the genotype ratio for F2 generation is 1:2:1.

Monohybrid Ratio for Monohybrid Cross:

Monohybrid ratio is defined as the phenotypic ratio of different types of offsprings (dominant and recessive) obtained in F2 generation of a monohybrid cross. In monohybrid cross experiment the phenotype ratio for F2 generation is 3:1.

Mendel’s Conclusions for Monohybrid Cross:

  • Characters such as a height of a stem, a color of seed etc. are inherited separately as discrete particles or unit. He called them a factor or a determiner. Now it is called a gene.
  • Each factor exists in contrasting or alternative forms. For e.g. for the height of a stem, there are two factors one for the tallness and other for the dwarfness. These two forms of genes are called alleles.
  • One of the factors is dominant and another factor is recessive. The only dominant factor expresses in the F1 generation.
  • In an organism, inheritance of each character is controlled by a pair of factors. One of the factors is contributed by the male parent and the other by the female parent. Thus higher organisms are diploid (2n)
  • From F2 generation Mendel concluded that in hybrid the two factors do not mix together but they just remain together.
  • During gamete the formation, they separate or segregate and each gamete receives only one factor from each pair of factors. Thus gametes are haploid (n).

Diagrammatic Representation of Monohybrid Cross

Test Cross or Back Cross:

This is the method devised by Mendel to test the genotype of F1 Hybrids. In F1 generation 25% of plants are dwarf and we can definitely say that their genotype is ‘tt’ (Homozygous). But in the case of a tall plant, there are 25 % pure tall plants and 50% hybrid tall plants. Hence in the case of tall plants genotype can be ‘TT’ (Homozygous) or ‘Tt’ (Heterozygous). Thus we are not sure of the genotype of tall plants in the F1 generation.

In a test cross, F1 hybrid is crossed with the homozygous recessive parent. Thus the offspring is crossed back with the parent, hence the test cross is also called a back cross.

If offspring has genotype (TT) then the F2 generation obtained will be 100 % tall. It can be explained as follows. The recessive parent can produce only one type of gamete ‘t’, and the offspring of the first generation can produce only one type of gamete ‘T’. Thus the progeny (F2 generation) will have genotype ‘Tt’ (tall).

If offspring has genotype (Tt) then the F2 generation obtained will be 50 % tall and 50 % dwarfs. It can be explained as follows. The recessive parent can produce only one type of gamete ‘t’, while the hybrid of the first generation can produce two types of gametes ‘T’ and ‘t’. Thus half the progeny (F2 generation) will have genotype ‘Tt’ (tall) and remaining half ‘tt’ (dwarf).

Diagrammatic Representation of Test Cross (With Flower Colour):

A test cross is a back cross but a back cross is not necessarily a test cross:

Case – 1: When the F1 generation is crossed with Recessive Parent:

The recessive parent can produce only one type of gamete ‘t’, while the hybrid of the first generation can produce two types of gametes ‘T’ and ‘t’. Thus half the progeny (F2 generation) will have genotype ‘Tt’ (tall) and remaining half ‘tt’ (dwarf).

Case – 2: When the F1 generation is crossed with Dominant Parent:

The dominant parent can produce only one type of gamete ‘T’, while the hybrid of the first generation can produce two types of gametes ‘T’ and ‘t’. Thus 100 % progeny is tall. half the progeny will have genotype ‘TT’ (Pure tall) and remaining half ‘Tt’ (Hybrid tall).

A test cross is a cross used to find the genotype of F1 generation. The test cross is a cross between an individual with the unknown genotype for a particular trait with a recessive plant for their trait, While back cross is a cross between an individual with the unknown genotype for a particular trait with a recessive or dominant plant for their trait. Back cross can not indicate the genotype of F1 generation. Hence a test cross is a back cross but a back cross is not a test cross.

The test cross method can be used to introduce useful recessive traits. Which is important in rapid crop improvement programmes.


RNA-sequencing highlights problems with gene expression in clones

In a study published Dec. 8 in the journal Proceedings of the National Academy of Sciences, Harris Lewin, professor in the University of California, Davis, Department of Evolution and Ecology, and colleagues in France and the U.S. used RNA sequencing to look at gene expression in cloned cows during implantation in order to get a better understanding of the molecular mechanisms that lead to a high rate of pregnancy failure for clones. The study is the culmination of 12 years of collaboration and combines the French team’s expertise in cloning and reproductive biology with the U.S. team’s expertise in functional genomics.

“Our work tackled fundamental questions relating to the cloning process,” said Lewin. “The study has resulted in the redefinition of our understanding of how nuclear reprogramming affects gene expression in extraembryonic tissues of cloned cattle embryos, and the exquisite communication between clones and their recipient mothers.”

“The large amount of data our collaboration has generated sheds light on mechanisms that account for embryonic losses at implantation,” said Olivier Sandra, team leader for the study at the Institut National de la Recherche Agronomique in France. “They also provide new insights on how events taking place at implantation drive the progression of pregnancy and shape the post-natal phenotype of the progeny, in cattle as well as in other mammalian species.”

The researchers studied tissue from cloned cow embryos — all derived from the same cell line — at 18 and 34 days of development, as well as the corresponding endometrial lining of the pregnant cows. They also looked at noncloned cows conceived using artificial insemination.

Using RNA sequencing, the researchers found multiple genes whose abnormal expression could lead to the high rate of death for cloned embryos, including failure to implant in the uterus and failure to develop a normal placenta. Looking at the extraembryonic tissue of the cloned cows at day 18, the researchers found anomalies in expression of more than 5,000 genes.


Bad reputation of crows demystified

In literature, crows and ravens are a bad omen and are associated with witches. Most people believe they steal, eat other birds' eggs and reduce the populations of other birds. But a new study, which has brought together over 326 interactions between corvids and their prey, demonstrates that their notoriety is not entirely merited.

Corvids -- the bird group that includes crows, ravens and magpies -- are the subject of several population control schemes, in both game and conservation environments. These controls are based on the belief that destroying them is good for other birds. They are also considered to be effective predators capable of reducing the populations of their prey.

However, a study published recently in the journal 'Ibis' analysed the impact of six species of corvid on a total of 67 species of bird susceptible to being their prey, among which are game birds and passerine birds.

The project, which compiled the information of 42 scientific studies and analysed a total of 326 interactions between corvids and their prey, shows that they have a much smaller effect on other bird species than was previously thought.

As Beatriz Arroyo -- author of the study and a researcher at the Institute of Research in Game Resources (IREC), a joint centre of the University of Castilla-La Mancha, the Castilla-La Mancha Community Council and the CSIC (Spanish National Research Council) -- says: "In 81% of cases studied, corvids did not present a discernible impact on their potential prey. Furthermore, in 6% of cases, some apparently beneficial relationships were even observed."

Greater impact on reproduction

To find out what impact corvids have on their prey, the researchers -- in conjunction with the University of Cape Town (South Africa) -- conducted several experiments in which they isolated crows, ravens and magpies, among other predators, to observe how they affected the reproduction and abundance of other birds.

According to the works analysed, when crows were taken away from their habitat, the survival rates of chickens and the number of eggs of other species were higher in most cases. Nevertheless, with respect to abundance, without corvids an increased size of the populations of other birds was observed only in a small number of cases.

According to the study, when crows were removed from the environment, in 46% of cases their prey had greater reproductive success, while their abundance fell in less than 10% of cases.

Additionally, these experimental studies carried out in nine different countries (Canada, France, Norway, Poland, Slovakia, Spain, Sweden, the UK and the USA) revealed that, if corvids are eliminated but other predators are not, the impact on the productivity of their prey would be positive in only 16% of cases whilst without corvids and other predators, including carnivores, the productivity of other birds improves in 60% of cases.

This suggests that crows, ravens and magpies, amongst others, have a lower impact on prey than other threats. "Compensatory predation can also occur," the researcher explains.

In the study they also compared the effects between different groups of corvids. In these results it is striking that "magpies had much less impact on prey than other species," Arroyo claims.

Comparing crows and magpies, the scientists showed that in 62% of cases crows impacted negatively on the reproduction of their prey, whilst magpies had a negative effect in 12% of cases. "But no differences related to the abundance of prey were noted," the scientist affirms.

For the authors of this piece of research, given the results it is necessary to "be cautious" when drawing conclusions on the impact of magpies or crows on the populations of their prey. "This method of managing populations is frequently ineffective and unnecessary," Arroyo finishes.


How Closely Related Are Humans to Apes?

To be human is to be a primate. Humans and chimpanzees, apes, tarsiers, vervets and more all share a common ancestor, and we’re clustered closely together on the tree of life.

The ancestors of Homo sapiens diverged from the ancestors of other primates at varying times, and that means we’re closely related to some primates, and more distantly related to others. There are two ways of thinking about how closely related we are to other primates: temporally and genetically.

The first merely asks how long ago we diverged from any given lineage of primates. Our ancestors split from chimpanzees, our closest relatives, along with bonobos, no more than 6 million years ago. We diverged from gorillas perhaps 10 million years ago, then orangutans around 14 million years ago. The split from gibbons is further back, and Old World Monkeys further still. So, we’re about 6 million years on from our shared history with any other living primate.

Genetically, we share more than 98 percent of our DNA with chimpanzees and bonobos. From this perspective, chimpanzees are mostly human and vice versa. But, in genetics, some changes matter more than others. That 1-plus percent of DNA that differs between our species has obviously led to some fairly significant changes .

We share about 96 percent of our DNA with gorillas, meaning that we’re, in a sense, more than twice as much like a chimpanzee as we are a gorilla. But, again, it’s not so simple when it comes to DNA. We are indeed very closely related to our ape counterparts. But the small differences between us have led to some extraordinarily big outcomes.

This story is part of an ongoing series exploring questions about human origins. Read more about ancient humans:


Watch the video: What Is the Difference Between a Raven and a Crow (February 2023).