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Mate Choice

Mate Choice

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.

The Ratio of X Chromosome to Autosomes

The Ratio of X Chromosome to Autosomes

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 Drosophila...

The Y Chromosome Determines Maleness

The Y Chromosome Determines Maleness

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. Today,...

Dosage Compensation

Dosage Compensation

In animals, gender is determined by the number and type of sex chromosome. For example, human females have two X chromosomes, and males have one X and one Y chromosome, whereas C.elegans with one X chromosome is a male, and the one with two X chromosomes is a hermaphrodite.
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Development of the Sexual Organs in the Embryo and Fetus

Development of the reproductive organs in an embryo starts from a bipotential state. This means the early embryo can develop either male or female reproductive organs. The formation of these organs begins with the growth of gonadal ridges that arise from the intermediate mesoderm during the fifth week of development.
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X and Y Chromosomes

X and Y Chromosomes

Among mammals, the gender of an organism is determined by the sex chromosomes. Humans have two sex chromosomes, X and Y. Every human diploid cell has 22 pairs of autosomes and one pair of sex chromosomes. A human female has two X chromosomes, while a male has one X chromosome and one Y chromosome.
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Related Experiment Video

Updated: May 23, 2026

Assessment of Sexual Behavior of Male Mice

Assessment of Sexual Behavior of Male Mice

Published on: March 5, 2020

Mammalian sexual dimorphism.

F J McPherson¹, P J Chenoweth

¹School of Animal and Veterinary Sciences, Charles Sturt University, Wagga Wagga, New South Wales, Australia.

Animal Reproduction Science

|April 10, 2012

Summary

Sexual dimorphisms (SDs) in mammals evolve for reproductive success, influenced by sexual selection and environmental factors. Understanding these dynamics aids wildlife preservation and livestock management.

Area of Science:

Evolutionary biology
Zoology
Animal behavior

Background:

Sexual dimorphisms (SDs) and secondary sexual characteristics (SSCs) evolve in mammals, primarily driven by sexual selection to enhance reproductive success, often favoring males.
These traits are more pronounced in polygynous, diurnal, and open-habitat species, and their expression can be altered by domestication and artificial selection.

Purpose of the Study:

To review current knowledge on the evolution, benefits, and costs of mammalian sexual dimorphisms.
To explore the interplay between natural and artificial selection in shaping SDs.
To draw conclusions beneficial for contemporary mammal husbandry and propagation.

Main Methods:

Literature review synthesizing existing research on mammalian sexual dimorphisms.

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Last Updated: May 23, 2026

Assessment of Sexual Behavior of Male Mice

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Analysis of evolutionary pressures, including sexual selection and environmental influences.

Examination of the impact of domestication and artificial selection on SDs.

Main Results:

Sexual selection drives the evolution of SDs, which may not always benefit individual survival.
Domestication can alter the expression of SDs, and artificial selection may have unintended consequences on linked traits.
Environmental changes can have significant phylogenetic implications for species relying on environmental cues for breeding and other activities.

Conclusions:

Understanding the evolutionary basis of SDs is crucial for wildlife preservation and livestock management.
Optimal outcomes in husbandry and propagation are achieved when artificial selection aligns with natural selection in supportive environments.
This review provides insights into the evolutionary rationale and practical applications of studying mammalian sexual dimorphisms.