생성자 호출 관련 질문

#include <iostream>
#include <string>
#include <vector>

using namespace std;

class Teacher {
	std::string m_name;
public:
	Teacher(const std::string& name_input = "No name")
		: m_name(name_input) {
		std::cout << "Teacher" << std::endl;
	}

	~Teacher() {}

	void setName(const std::string& name_in) {
		m_name = name_in;
	}

	std::string getName() {
		return m_name;
	}

	friend std::ostream& operator<<(std::ostream& os, const Teacher& teacher) {
		os << teacher.m_name << std::endl;
		return os;
	}
};

class Student {
	std::string m_name;
	int m_intel;
public:
	Student(const std::string& name_in = "No name", const int& intel_in = 0)
		: m_name(name_in)
		, m_intel(intel_in) {
		std::cout << "Student" << std::endl;
	}

	~Student() {}

	void setName(const std::string& name_in) {
		m_name = name_in;
	}

	void setIntel(const int& intel_in) {
		m_intel = intel_in;
	}

	int getIntel() {
		return m_intel;
	}

	friend std::ostream& operator<<(std::ostream& os, const Student& student) {
		os << student.m_name << " " << student.m_intel;
		return os;
	}
};

class Lecture {
	std::string m_name;
	Teacher m_teacher;
	std::vector<Student> m_students;
public:
	Lecture(const std::string& name_in = "No Name")
		: m_name(name_in) {
		std::cout << "Lecture" << std::endl;
	}

	~Lecture() {
		//do Not delete teacher, students
	}

	void assignTeacher(const Teacher& teacher) {
		m_teacher = teacher;
	}

	void registerStudent(const Student& const student) {
		m_students.push_back(student);
	}

	void study() {
		std::cout << m_name << " Study " << std::endl << std::endl;

		for (auto& element : m_students)
			element.setIntel(element.getIntel() + 1);
	}

	friend std::ostream& operator<<(std::ostream& os, const Lecture& lecture) {
		os << "Lecture name : " << lecture.m_name << std::endl;

		os << lecture.m_teacher;

		for (auto& element : lecture.m_students)
			os << element << std::endl;

		return os;
	}
};

int main() {
	using namespace std;

	Lecture lec1("Introduction to Computer Programming");
	lec1.assignTeacher(Teacher("Prof. Hong"));
	lec1.registerStudent(Student("A", 1));
	lec1.registerStudent(Student("B", 2));
	lec1.registerStudent(Student("C", 3));

	Lecture lec2("Computational Thinking");
	lec2.assignTeacher(Teacher("Prof. Good"));
	lec2.registerStudent(Student("A", 0));

	//TODO. implement Aggregation Relationship

	//test
	{
		cout << lec1 << endl;
		cout << lec2 << endl;

		lec2.study();

		cout << lec1 << endl;
		cout << lec2 << endl;
	}


}

Lecture를 생성하면 Teacher도 같이 생성됩니다

그런데 Lecture 생성자 안에 Teacher와 관련된건 없을텐데 생성되니깐 궁금해서 질문합니다