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Related Concept Videos

Mate Choice01:20

Mate Choice

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Mate choice—the decision about whom to mate with—is a type of natural selection, since animals must reproduce to pass down their genes. Mate choice is also called intersexual selection because the behavior occurs between the sexes.
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Testing a Claim about Mean: Unknown Population SD01:21

Testing a Claim about Mean: Unknown Population SD

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A complete procedure of testing a hypothesis about a population mean when the population standard deviation is unknown is explained here.
Estimating a population mean requires the samples to be approximately normally distributed. The data should be collected from the randomly selected samples having no sampling bias. There is no specific requirement for sample size. But if the sample size is less than 30, and we don't know the population standard deviation, a different approach is used;...
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The Y Chromosome Determines Maleness02:19

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The Y chromosome is a sex chromosome found in several vertebrates and mammals, including humans. In addition to 22 pairs of autosomes, the human males have one X chromosome and one Y chromosome. In these organisms, the presence or absence of the Y chromosome determines the development of male traits.
Evolution
Around 300 million years ago, the two sex chromosomes diverged from two identical autosomal chromosomes. Over time, the Y chromosome has lost most of its genes, shrinking in size....
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The Ratio of X Chromosome to Autosomes02:45

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In most organisms, sex is determined by the ratio of X and Y chromosomes. However, in some organisms, such as Drosophila and C.elegans, sex is determined by the ratio of the number of X chromosomes to the number of sets of autosomes. The Y chromosome in Drosophila is active but does not determine sex. It contains genes responsible for the production of sperms in adult flies.  
Normal male Drosophila has a ratio of one X chromosome to two sets of autosomes. In contrast, normal female...
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Natural Selection and Mating Preferences01:06

Natural Selection and Mating Preferences

214
The principle of natural selection posits that organisms better adapted to their environment are more likely to survive and reproduce. This principle is closely intertwined with mating preferences, a key aspect of sexual selection, which evolutionary psychologists believe is driven by instincts to propagate one's genes. Such instincts significantly influence mating behaviors and preferences between genders.
Females, due to their biological roles in conception, pregnancy, and nursing,...
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Types of Selection01:46

Types of Selection

42.6K
Natural selection influences the frequencies of particular alleles and phenotypes within populations in several different ways. Primarily, natural selection can be directional, stabilizing, or disruptive. Directional selection favors one extreme trait and shifts the population towards that phenotype while selecting against individuals displaying alternate traits. Stabilizing selection favors an intermediate trait with a narrow range of variation. Deviation from the optimal phenotype towards an...
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Related Experiment Video

Updated: Oct 16, 2025

Peering into the Dynamics of Social Interactions: Measuring Play Fighting in Rats
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Sex Differences in Spotted Hyenas.

S Kevin McCormick1,2, Kay E Holekamp1,2, Laura Smale1,2,3

  • 1Department of Integrative Biology, Michigan State University, East Lansing, Michigan 48824, USA.

Cold Spring Harbor Perspectives in Biology
|October 15, 2021
PubMed
Summary
This summary is machine-generated.

Female spotted hyenas exhibit "masculinized" traits like aggression, crucial for food access, unlike typical mammalian sex differences. These adaptations are driven by natural selection for reproductive success.

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Area of Science:

  • Zoology
  • Behavioral Ecology
  • Mammalian Biology

Background:

  • Spotted hyenas display apparent virilization in females, prompting investigation into sex differences.
  • Existing research highlights a mosaic of dimorphic traits, some aligning with mammalian norms, others reversed.

Purpose of the Study:

  • To review and analyze sex differences in spotted hyena behavior and morphology.
  • To understand the evolutionary pressures shaping these unique dimorphic traits.

Main Methods:

  • Comparative review of existing literature on spotted hyena behavior and morphology.
  • Analysis of documented sex differences in traits such as social dominance, dispersal, and reproduction.

Main Results:

  • Spotted hyenas show reversed sex differences in aggression, social dominance, and territory defense compared to other mammals.
  • Females are slightly larger as adults, with no differences in neonatal body mass or hunting behavior.
  • Early androgen exposure may enhance female aggressiveness, linked to food acquisition.

Conclusions:

  • "Masculinized" female traits, particularly aggression, are adaptations for securing food, essential for reproductive success due to high energetic costs.
  • Natural selection has modified food-related traits while leaving non-food-related dimorphisms consistent with other mammals.